Henri GWET | ECOLE NATIONALE SUPERIEURE POLYTECHNIQUE de YAOUNDE (original) (raw)

Papers by Henri GWET

BMC Public Health, 2010

Background: Coinfection with hepatitis B virus (HBV) or hepatitis C virus (HCV) in HIV-infected p... more Background: Coinfection with hepatitis B virus (HBV) or hepatitis C virus (HCV) in HIV-infected patients receiving a commonly used nevirapine-based antiretroviral therapy is a major concern for African clinicians owing to its high prevalence, the infrequent testing and treatment of viral hepatitis, and the impact of liver disease on the tolerability and effectiveness of anti-HIV treatment. We compared the hepatotoxicity and the immunological, virological and clinical effectiveness of a nevirapine-based antiretroviral therapy between patients infected with HIV only and patients coinfected with hepatitis B or C virus in Cameroon. Methods: A retrospective cohort study was conducted among HIV-1-infected patients. Plasma HBV DNA and HCV RNA were tested in positive or indeterminate samples for HBsAg or HCV antibodies, respectively. All patients received nevirapine and lamivudine plus stavudine or zidovudine. Results: Of 169 HIV-1-infected patients with a median baseline CD4 count of 135 cells/mm 3 (interquartile range [IQR] 67-218), 21% were coinfected with HBV or HCV. In coinfected patients, the median viral load was 2.47 × 10 7 IU/mL for HBV (IQR 3680-1.59 × 10 8 ) and 928 000 IU/mL for HCV (IQR 178 400-2.06 × 10 6 ). Multivariate analyses showed that the risk of hepatotoxicity was 2-fold higher in coinfected patients (p < 0.01). The response to antiretroviral therapy was however comparable between monoinfected and coinfected patients in terms of CD4 cell count increase (p = 0.8), HIV-1 viral load below 400 copies/mL (p = 0.9), death (p = 0.3) and death or new AIDS-defining event (p = 0.1). Nevirapine was replaced by a protease inhibitor in 4 patients owing to hepatotoxicity. Conclusion: This study suggests that the nevirapine-based antiretroviral therapy could be used safely as first-line treatment in patients with low CD4 cell count in Africa despite frequent coinfections with HBV or HCV and infrequent testing of these infections. Although testing for HBV and HCV should be systematically performed before initiating antiretroviral therapy, transaminases elevations at baseline or during treatment should be a decisive argument for testing when hepatitis status is unknown.

BMC Infectious Diseases, 2015

Despite the progress in the Prevention of the Mother-to-Child Transmission of HIV (PMTCT), the pa... more Despite the progress in the Prevention of the Mother-to-Child Transmission of HIV (PMTCT), the paediatric HIV epidemic remains worrying in Cameroon. HIV prevalence rate for the population of pregnant women was 7.6 % in 2010 in Cameroon. The extent of the paediatric HIV epidemic is needed to inform policymakers. We developed a stochastic simulation model to estimate the number of new paediatric HIV infections through MTCT based on the observed uptake of services during the different steps of the PMTCT cascade in Cameroon in 2011. Different levels of PMTCT uptake was also assessed. A discrete events computer simulation-based approach with stochastic structure was proposed to generate a cohort of pregnant women followed-up until 6 weeks post-partum, and optionally until complete breastfeeding cessation in both prevalent and incident lactating HIV-infected women. The different parameters of the simulation model were fixed using data sources available from the 2011 national registry surveys, and from external cohorts in Cameroon. Different PMTCT coverages were simulated to assess their impact on MTCT. Available data show a low coverage of PMTCT services in Cameroon in 2011. Based on a simulation approach on a population of 995, 533 pregnant women, the overall residual MTCT rate in 2011 was estimated to be 22.1 % (95 % CI: 18.6 %-25.2 %), the 6-week perinatal MTCT rate among prevalent HIV-infected mothers at delivery is estimated at 12.1 % (95 % CI: 8.1 %-15.1 %), with an additional postnatal MTCT rate estimated at 13.3 % (95 % CI: 9.3 %-17.8 %). The MTCT rate among children whose mothers seroconverted during breastfeeding was estimated at 20.8 % (95 % CI: 14.1 %-26.9 %). Overall, we estimated the number of new HIV infections in children in Cameroon to be 10, 403 (95 % CI: 9, 054-13, 345) in 2011. When PMTCT uptake have been fixed at 100 %, 90 % and 80 %, global MTCT rate failed to 0.9 % (95 % CI: 0.5 %-1.7 %), 2.0 % (95 % CI: 0.9 %-3.2 %) and 4.3 % (95 % CI: 2.4 %-6.7 %) respectively. This model is helpful to provide MTCT estimates to guide the national HIV policy in Cameroon. Increasing supply and uptake of PMTCT services among prevalent HIV infected pregnant women, as well as HIV-prevention interventions including the offer and acceptance of HIV testing and counselling in lactating women could reduce significantly the residual HIV MTCT in Cameroon. A public health effort should be made to encourage health care workers and pregnant women to use PMTCT services until complete breastfeeding cessation.

RÉSUMÉ. Le point central de ce travail est de proposer une nouvelle approche dans la définition d... more RÉSUMÉ. Le point central de ce travail est de proposer une nouvelle approche dans la définition des indicateurs de mesure de l'efficacité d'un système de transport. Une telle démarche nous paraît nécessaire chaque fois que l'on manipule des objets mal définis. C'est particulièrement le cas lorsque l'on traite des informations sur le transport des produits vivriers. Nous utilisons un différentiel sémantique pour saisir de telles informations. Les facteurs caractéristiques de l'organisation du transport sont vues comme des ensembles flous et dédoublé afin de permettre une comparaison multicritère. À la fin du travail, nous effectuons une comparaison entre notre modèle d'indicateur et un indicateur analytique issue de l'analyse des correspondances multiples. MOTS-CLÉS : indicateur, logique floue, analyse multicritères, codage de données, questionnaire flou, produits vivriers.

Dans plusieurs domaines de la science, la nature des données rend parfois difficile la constructi... more Dans plusieurs domaines de la science, la nature des données rend parfois difficile la construction et l'analyse des tableaux de données par les méthodes traditionnelles de la statistique descriptive. Il s'agit le plus souvent de connaissances imprécises ou vagues que l'on peut avoir d'un phénomène donné. Si à la question « quel âge avez-vous ? », l'on répond « environ 30 ans », une telle réponse ne peut pas être vue comme un caractère statistique au sens classique du terme. Le problème se pose ici au niveau de l'ensemble des observations possibles. Cet ensemble n'est pas net, il est flou. D'où la nécessité de préciser la notion de caractère statistique flou, et plus précisément de caractère qualitatif flou pour lequel nous proposons une interprétation en terme de sous-ensemble. Si la notion de probabilité semble appropriée pour traiter des événements incertains, celle de possibilité est plus indiquée quand les événements sont imprécis.

The definition of a symmetrical difference from the fuzzy implication operators has enabled us to... more The definition of a symmetrical difference from the fuzzy implication operators has enabled us to prove the notion of distance that extends Tchebytchev's distance in the case of fuzzy characters. In the following write up, we are going to show how we can construct a measure of the proximity between two modalities of characters from this distance notion in a fuzzy two dimensional statistical description.

Malaria Journal, 2010

Background: The use of drug combinations, including non-artemisinin-based and artemisinin-based c... more Background: The use of drug combinations, including non-artemisinin-based and artemisinin-based combination therapy (ACT), is a novel strategy that enhances therapeutic efficacy and delays the emergence of multidrugresistant Plasmodium falciparum. Its use is strongly recommended in most sub-Saharan African countries, namely Cameroon, where resistance to chloroquine is widespread and antifolate resistance is emerging. Methods: Studies were conducted in Cameroonian children with acute uncomplicated P. falciparum malaria according to the standard World Health Organization protocol at four sentinel sites between 2003 and 2007. A total of 1,401 children were enrolled, of whom 1,337 were assigned to randomized studies and 64 were included in a single non-randomized study. The proportions of adequate clinical and parasitological response (PCRuncorrected on day 14 and PCR-corrected on day 28) were the primary endpoints to evaluate treatment efficacy on day 14 and day 28. The relative effectiveness of drug combinations was compared by a multi-treatment Bayesian random-effect meta-analysis. Findings: The results based on the meta-analysis suggested that artesunate-amodiaquine (AS-AQ) is as effective as other drugs (artesunate-sulphadoxine-pyrimethamine [AS-SP], artesunate-chlorproguanil-dapsone [AS-CD], artesunate-mefloquine [AS-MQ], dihydroartemisinin-piperaquine [DH-PP], artemether-lumefantrine [AM-LM], amodiaquine, and amodiaquine-sulphadoxine-pyrimethamine [AQ-SP])

Recherche Transports Securite, 1998

In 1996 inrets carried out road haulage pricing surveys in seven countries in three continents, A... more In 1996 inrets carried out road haulage pricing surveys in seven countries in three continents, Africa, South-East Asia and Latin America, in order to gain a clearer picture of the higher cost of transport in Africa. There is a considerable variation in the unit costs of road haulage within a particular country, indeed this variation is greater than the variation between the average price in different countries. In particular, the tonnage which is transported and the distance involved have a major influence on the price per tonne x kilometre. In order to quantify the differences in price which exist between different countries it is therefore necessary to define an indicator which takes account of the main factors which determine prices, other than the country. Varied types of statistical analysis, in particular involving modelling, have been used to indicate how these parameters affect the tariffs of transport in each country and estimate the average price for each country for a particular distance or tonnage. The selected indicators all agree that over long distances road haulage is significantly more expensive in Africa than in Asia. There are differences between the African countries, Cameroon being the most expensive.

Les Cahiers Scientifiques du Transport, 2000

L 'inefficacité des systèmes de transport constitue probablement l 'un des principaux points de ... more L 'inefficacité des systèmes de transport constitue probablement l 'un des principaux points
de blocage au développement des économies africaines. A la fin des années 80, peu avant
la dévaluation du franc CFA, le surcoût de transport pénalisait sérieusement la compétitivité
des produits africains exportés et renchérissait également le prix des produits consommés
sur place, ce qui a conduit notamment la Banque Mondiale à élaborer un Programme de
Politique des transports en Afrique Sub-Saharienne.

JOURNAL OF FUZZY MATHEMATICS, 2002

This paper provides a new way of multi-criteria evaluation. This method is based on the use of f... more This paper provides a new way of multi-criteria evaluation. This method is based on the use of
fuzzy set connectives and fuzzy measures. At the end, we make some comparisons between new
and old ways.

JOURNAL OF FUZZY MATHEMATICS, 2001

In this paper, we have introduced a new notion of logic equivalence based on a parametric family... more In this paper, we have introduced a new notion of logic equivalence based on a
parametric family of fuzzy operators. This equivalence operator has helped us to define a new
dissimilarity index for fuzzy sets. Our index is the fuzzy counterpart of a series of distances
commonly uses in Data Analysis and in particular the cardinal distance of the symmetric
difference. From what follows, we used this dissimilarity to define a new efficiency indicator
for a transport system. This has been made possible with the use of fuzzy uncoupling and its
interpretation in terms of fuzzy logic connectives. We used these new tools on the data from an
investigation that we carried out concerning the transportation of foodstuff in Cameroon.

European Journal of Plant Pathology, Feb 2013

Pod rot causes up to 30 % losses in world cocoa production. In order to predict the risk evolutio... more Pod rot causes up to 30 % losses in world cocoa production. In order to predict the risk evolution of disease, it is important to take into consideration the developmental stage of fruits. In fact, it has been shown that the risk of attack by pod rot depends amongst others on the developmental stage of fruits. We proposed here to estimate the susceptibility at different stages. Susceptibility of fruit to disease was investigated at three fruit developmental stages (cherelle, young pod and adult pod); disease severity was assessed in laboratory conditions, on detached, artificially inoculated fruits, while disease incidence was assessed in the field, under natural inoculum pressure. In both assessment fruits at the cherelle stage were the most susceptible whereas the young and adult fruits were equally susceptible. The vertical position of the fruits on the tree did not influence their susceptibility. Estimates of the fruit susceptibility and of the infectious potential were derived from the severity and incidence measurements, using a model assuming that the number of spores on a fruit follows a Poisson distribution with the mean, the density of spores per fruit as the parameter. The estimated parameter values allowed the evaluation of the probability of attack of a fruit by the disease, which could be implemented in a disease warning system.

Journal of the Royal Statistical Society: Series C (Applied Statistics)

In the estimation of a lifetime distribution from regular interval-censored data with an addition... more In the estimation of a lifetime distribution from regular interval-censored data with an additional censoring variable, we focus on the case where (contrary to the actuarial method) both events (interest and censorship) can occur on a given individual in the same interval and, thus, are observed simultaneously. Specifically, we consider a population where individuals pass through a finite number of successive stages during their growth and are threatened by a disease. First, we estimate the lifetime and time-to-disease distributions in each developmental stage from such censored data. Using data that were recorded on a cohort of individuals followed over a long period of time, we propose a non-parametric, yet continuously differentiable and piecewise quadratic polynomial, estimator for the survival function of each of these distributions. We applied it to estimate, from weekly field observations in Mbankomo (Cameroon), the lifetime and time-to-disease distributions of cocoa fruits in each of their three developmental stages before maturity. It is found that on average a healthy cocoa fruit spends only inline image weeks in its first stage (cherelle), compared with nearly 9 weeks as a young pod and inline image weeks as an adult pod. In a second phase, however, adapting our methodology to competing risks estimation, we observed that, owing to the severe rate of attacks, the fruits' effective lifetime expectancy in farmland is much shorter. Indeed, in that part of Cameroon, the cumulative risk of an attack on cocoa fruits in farmland, especially by pod rot disease, far outweighs their chances of reaching maturity.

Health and system science, 1997

Dans cet article, nous proposons une méthode de saisie et d'analyse des connaissances imprécises.... more Dans cet article, nous proposons une méthode de saisie et d'analyse des connaissances imprécises. Les éléments de la théorie des sous-ensembles flous sont utilisés pour offrir à l'observateur la possibilité d'avoir un choix de réponse discret aux questions qui lui sont posées dans le cadre d'une enquête. Nous proposons par la suite un ensemble d'outils pour analyser ce type de questionnaire. Une enquête tirée de la pédiatrie et mettant en œuvre l'ensemble de ces méthodes est proposée.

IMHOTEP, 2000

La de nition d'une di erence symetrique a partir des operateurs d'implication oue nous a ... more La de nition d'une di erence symetrique a partir des operateurs d'implication

oue nous a permis de mettre en evidence une notion de distance
qui etend celle de Tchebytchev au cas
ou. Nous montrons par la suite
comment on peut, a partir de cette distance, construire une mesure de
la proximite entre deux modalites de caracteres dans une description
statistique
oue a deux dimensions.

Statistics in medicine, Apr 23, 2013

Multiple imputation is commonly used to impute missing covariate in Cox semiparametric regression... more Multiple imputation is commonly used to impute missing covariate in Cox semiparametric regression setting. It is to fill each missing data with more plausible values, via a Gibbs sampling procedure, specifying an imputation model for each missing variable. This imputation method is implemented in several softwares that offer imputation models steered by the shape of the variable to be imputed, but all these imputation models make an assumption of linearity on covariates effect. However, this assumption is not often verified in practice as the covariates can have a nonlinear effect. Such a linear assumption can lead to a misleading conclusion because imputation model should be constructed to reflect the true distributional relationship between the missing values and the observed values. To estimate nonlinear effects of continuous time invariant covariates in imputation model, we propose a method based on B-splines function. To assess the performance of this method, we conducted a simulation study, where we compared the multiple imputation method using Bayesian splines imputation model with multiple imputation using Bayesian linear imputation model in survival analysis setting. We evaluated the proposed method on the motivated data set collected in HIV-infected patients enrolled in an observational cohort study in Senegal, which contains several incomplete variables. We found that our method performs well to estimate hazard ratio compared with the linear imputation methods, when data are missing completely at random, or missing at random. Copyright © 2013 John Wiley & Sons, Ltd.

Recherche - Transports - Sécurité, Sep 1998

In 1996 inrets carried out road haulage pricing surveys in seven countries in three continents, A... more In 1996 inrets carried out road haulage pricing surveys in seven countries in three continents, Africa, South-East Asia and Latin America, in order to gain a clear picture of the higher cost of transport in Africa. There is a considerable variation in the unit costs of road haulage within a particular country, indeed this variation is greater than the variation between the average price in different countries. In particular, the tennage which is transported and the distance involved have a major influence on the price per torine x kilometre. In order to quantify the differences in price which exist between different countries it is therefore necessary to define an indicator which takes account of the main factors which determine prices, other than the country. Varied types of satistical analysis, in particular involving modelling have been used to indicate how these parameter affect the tariffs of transport in each country and estimate the average price for each country for a particular distance or tonnage. The selected indicators all agree that over long distances road haulage is significantly more expensive in Africa than in Asia. There are differences between the African countries, Cameroon being the most expensive.

BMC Medical Research Methodology, 2010

Background: Malaria remains a burden in Sub-Saharan Countries. The strategy proposed by the World... more Background: Malaria remains a burden in Sub-Saharan Countries. The strategy proposed by the World Health Organization (WHO) is to systematically compare the therapeutic efficacy of antimalarial drugs using as primary outcome for efficacy, a four-category ordered criterion. The objective of the present work was to analyze the treatment effects on this primary outcome taking into account both a center-effect and individual covariates. A three-arm, threecentre trial of Amodiaquine (AQ), sulfadoxine-pyrimethamine (SP) and their combination (AQ + SP), conducted by OCEAC-IRD in 2003, in 538 children with uncomplicated Plasmodium falciparum malaria, is used as an illustration. Methods: Analyses were based on ordinal regression methods, assuming an underlying continuous latent variable, using either the proportional odds (PO) or the proportional hazards (PH) models. Different algorithms, corresponding to both frequentist-and bayesian-approaches, were implemented using the freely available softwares R and Winbugs, respectively. The performances of the different methods were evaluated on a simulated data set, and then they were applied on the trial data set. Results: Good coverage probability and type-1 error for the treatment effect were achieved. When the methods were applied on the trial data set, results highlighted a significance decrease of SP efficacy when compared to AQ (PO, odds ratio [OR] 0.14, 95% confidence interval [CI] 0.04-0.57; hazard ratio [HR] 0.605, 95% CI 0.42-0.82), and an equal effectiveness between AQ + SP and AQ (PO, odds ratio [OR] 1.70, 95% confidence interval [CI] 0.25-11.44; hazard ratio [HR] 1.40, 95% CI 0.88-2.18). The body temperature was significantly related to the responses. The patient weights were marginally associated to the clinical response. Conclusion: The proposed analyses, based on usual statistical packages, appeared adapted to take into account the full information contained in the four categorical outcome in malaria trials, as defined by WHO, with the possibility of adjusting on individual and global covariates.

International Journal of Uncertainty, Fuzziness and Knowledge-based Systems, 1997

In this article, we introduce a general concept of fuzzy operators. These operators are then used... more In this article, we introduce a general concept of fuzzy operators. These operators are then used to generalize the possibilistic conditioning formulation proposed by Nguyen [1]. This generalization depends on the relation which exists between this conditioning and the probabilistic t-norm. By using other t-norms, other conditionings are obtained, and their properties are studied. One application of normalized possibilistic conditioning is the measure of the dependency between two fuzzy statistical variables. The measure constructed can be considered as the possibilistic counterpart of mutual information commonly used in statistics.

Malaria Journal, 2010

Background The use of drug combinations, including non-artemisinin-based and artemisinin-based co... more Background The use of drug combinations, including non-artemisinin-based and artemisinin-based combination therapy (ACT), is a novel strategy that enhances therapeutic efficacy and delays the emergence of multidrug-resistant Plasmodium falciparum. Its use is strongly recommended in most sub-Saharan African countries, namely Cameroon, where resistance to chloroquine is widespread and antifolate resistance is emerging. Methods Studies were conducted in Cameroonian children with acute uncomplicated P. falciparum malaria according to the standard World Health Organization protocol at four sentinel sites between 2003 and 2007. A total of 1,401 children were enrolled, of whom 1,337 were assigned to randomized studies and 64 were included in a single non-randomized study. The proportions of adequate clinical and parasitological response (PCR-uncorrected on day 14 and PCR-corrected on day 28) were the primary endpoints to evaluate treatment efficacy on day 14 and day 28. The relative effectiveness of drug combinations was compared by a multi-treatment Bayesian random-effect meta-analysis. Findings The results based on the meta-analysis suggested that artesunate-amodiaquine (AS-AQ) is as effective as other drugs (artesunate-sulphadoxine-pyrimethamine [AS-SP], artesunate-chlorproguanil-dapsone [AS-CD], artesunate-mefloquine [AS-MQ], dihydroartemisinin-piperaquine [DH-PP], artemether-lumefantrine [AM-LM], amodiaquine, and amodiaquine-sulphadoxine-pyrimethamine [AQ-SP]). AM-LM appeared to be the most effective with no treatment failure due to recrudescence, closely followed by DH-PP. Conclusion Although AM-LM requires six doses, rather than three doses for other artemisinin-based combinations, it has potential advantages over other forms of ACT. Further studies are needed to evaluate the clinical efficacy and tolerance of these combinations in different epidemiological context.

BMC Public Health, 2010

Background: Coinfection with hepatitis B virus (HBV) or hepatitis C virus (HCV) in HIV-infected p... more Background: Coinfection with hepatitis B virus (HBV) or hepatitis C virus (HCV) in HIV-infected patients receiving a commonly used nevirapine-based antiretroviral therapy is a major concern for African clinicians owing to its high prevalence, the infrequent testing and treatment of viral hepatitis, and the impact of liver disease on the tolerability and effectiveness of anti-HIV treatment. We compared the hepatotoxicity and the immunological, virological and clinical effectiveness of a nevirapine-based antiretroviral therapy between patients infected with HIV only and patients coinfected with hepatitis B or C virus in Cameroon. Methods: A retrospective cohort study was conducted among HIV-1-infected patients. Plasma HBV DNA and HCV RNA were tested in positive or indeterminate samples for HBsAg or HCV antibodies, respectively. All patients received nevirapine and lamivudine plus stavudine or zidovudine. Results: Of 169 HIV-1-infected patients with a median baseline CD4 count of 135 cells/mm 3 (interquartile range [IQR] 67-218), 21% were coinfected with HBV or HCV. In coinfected patients, the median viral load was 2.47 × 10 7 IU/mL for HBV (IQR 3680-1.59 × 10 8 ) and 928 000 IU/mL for HCV (IQR 178 400-2.06 × 10 6 ). Multivariate analyses showed that the risk of hepatotoxicity was 2-fold higher in coinfected patients (p < 0.01). The response to antiretroviral therapy was however comparable between monoinfected and coinfected patients in terms of CD4 cell count increase (p = 0.8), HIV-1 viral load below 400 copies/mL (p = 0.9), death (p = 0.3) and death or new AIDS-defining event (p = 0.1). Nevirapine was replaced by a protease inhibitor in 4 patients owing to hepatotoxicity. Conclusion: This study suggests that the nevirapine-based antiretroviral therapy could be used safely as first-line treatment in patients with low CD4 cell count in Africa despite frequent coinfections with HBV or HCV and infrequent testing of these infections. Although testing for HBV and HCV should be systematically performed before initiating antiretroviral therapy, transaminases elevations at baseline or during treatment should be a decisive argument for testing when hepatitis status is unknown.

BMC Public Health, 2010

Background: Coinfection with hepatitis B virus (HBV) or hepatitis C virus (HCV) in HIV-infected p... more Background: Coinfection with hepatitis B virus (HBV) or hepatitis C virus (HCV) in HIV-infected patients receiving a commonly used nevirapine-based antiretroviral therapy is a major concern for African clinicians owing to its high prevalence, the infrequent testing and treatment of viral hepatitis, and the impact of liver disease on the tolerability and effectiveness of anti-HIV treatment. We compared the hepatotoxicity and the immunological, virological and clinical effectiveness of a nevirapine-based antiretroviral therapy between patients infected with HIV only and patients coinfected with hepatitis B or C virus in Cameroon. Methods: A retrospective cohort study was conducted among HIV-1-infected patients. Plasma HBV DNA and HCV RNA were tested in positive or indeterminate samples for HBsAg or HCV antibodies, respectively. All patients received nevirapine and lamivudine plus stavudine or zidovudine. Results: Of 169 HIV-1-infected patients with a median baseline CD4 count of 135 cells/mm 3 (interquartile range [IQR] 67-218), 21% were coinfected with HBV or HCV. In coinfected patients, the median viral load was 2.47 × 10 7 IU/mL for HBV (IQR 3680-1.59 × 10 8 ) and 928 000 IU/mL for HCV (IQR 178 400-2.06 × 10 6 ). Multivariate analyses showed that the risk of hepatotoxicity was 2-fold higher in coinfected patients (p < 0.01). The response to antiretroviral therapy was however comparable between monoinfected and coinfected patients in terms of CD4 cell count increase (p = 0.8), HIV-1 viral load below 400 copies/mL (p = 0.9), death (p = 0.3) and death or new AIDS-defining event (p = 0.1). Nevirapine was replaced by a protease inhibitor in 4 patients owing to hepatotoxicity. Conclusion: This study suggests that the nevirapine-based antiretroviral therapy could be used safely as first-line treatment in patients with low CD4 cell count in Africa despite frequent coinfections with HBV or HCV and infrequent testing of these infections. Although testing for HBV and HCV should be systematically performed before initiating antiretroviral therapy, transaminases elevations at baseline or during treatment should be a decisive argument for testing when hepatitis status is unknown.

BMC Infectious Diseases, 2015

Despite the progress in the Prevention of the Mother-to-Child Transmission of HIV (PMTCT), the pa... more Despite the progress in the Prevention of the Mother-to-Child Transmission of HIV (PMTCT), the paediatric HIV epidemic remains worrying in Cameroon. HIV prevalence rate for the population of pregnant women was 7.6 % in 2010 in Cameroon. The extent of the paediatric HIV epidemic is needed to inform policymakers. We developed a stochastic simulation model to estimate the number of new paediatric HIV infections through MTCT based on the observed uptake of services during the different steps of the PMTCT cascade in Cameroon in 2011. Different levels of PMTCT uptake was also assessed. A discrete events computer simulation-based approach with stochastic structure was proposed to generate a cohort of pregnant women followed-up until 6 weeks post-partum, and optionally until complete breastfeeding cessation in both prevalent and incident lactating HIV-infected women. The different parameters of the simulation model were fixed using data sources available from the 2011 national registry surveys, and from external cohorts in Cameroon. Different PMTCT coverages were simulated to assess their impact on MTCT. Available data show a low coverage of PMTCT services in Cameroon in 2011. Based on a simulation approach on a population of 995, 533 pregnant women, the overall residual MTCT rate in 2011 was estimated to be 22.1 % (95 % CI: 18.6 %-25.2 %), the 6-week perinatal MTCT rate among prevalent HIV-infected mothers at delivery is estimated at 12.1 % (95 % CI: 8.1 %-15.1 %), with an additional postnatal MTCT rate estimated at 13.3 % (95 % CI: 9.3 %-17.8 %). The MTCT rate among children whose mothers seroconverted during breastfeeding was estimated at 20.8 % (95 % CI: 14.1 %-26.9 %). Overall, we estimated the number of new HIV infections in children in Cameroon to be 10, 403 (95 % CI: 9, 054-13, 345) in 2011. When PMTCT uptake have been fixed at 100 %, 90 % and 80 %, global MTCT rate failed to 0.9 % (95 % CI: 0.5 %-1.7 %), 2.0 % (95 % CI: 0.9 %-3.2 %) and 4.3 % (95 % CI: 2.4 %-6.7 %) respectively. This model is helpful to provide MTCT estimates to guide the national HIV policy in Cameroon. Increasing supply and uptake of PMTCT services among prevalent HIV infected pregnant women, as well as HIV-prevention interventions including the offer and acceptance of HIV testing and counselling in lactating women could reduce significantly the residual HIV MTCT in Cameroon. A public health effort should be made to encourage health care workers and pregnant women to use PMTCT services until complete breastfeeding cessation.

RÉSUMÉ. Le point central de ce travail est de proposer une nouvelle approche dans la définition d... more RÉSUMÉ. Le point central de ce travail est de proposer une nouvelle approche dans la définition des indicateurs de mesure de l'efficacité d'un système de transport. Une telle démarche nous paraît nécessaire chaque fois que l'on manipule des objets mal définis. C'est particulièrement le cas lorsque l'on traite des informations sur le transport des produits vivriers. Nous utilisons un différentiel sémantique pour saisir de telles informations. Les facteurs caractéristiques de l'organisation du transport sont vues comme des ensembles flous et dédoublé afin de permettre une comparaison multicritère. À la fin du travail, nous effectuons une comparaison entre notre modèle d'indicateur et un indicateur analytique issue de l'analyse des correspondances multiples. MOTS-CLÉS : indicateur, logique floue, analyse multicritères, codage de données, questionnaire flou, produits vivriers.

Dans plusieurs domaines de la science, la nature des données rend parfois difficile la constructi... more Dans plusieurs domaines de la science, la nature des données rend parfois difficile la construction et l'analyse des tableaux de données par les méthodes traditionnelles de la statistique descriptive. Il s'agit le plus souvent de connaissances imprécises ou vagues que l'on peut avoir d'un phénomène donné. Si à la question « quel âge avez-vous ? », l'on répond « environ 30 ans », une telle réponse ne peut pas être vue comme un caractère statistique au sens classique du terme. Le problème se pose ici au niveau de l'ensemble des observations possibles. Cet ensemble n'est pas net, il est flou. D'où la nécessité de préciser la notion de caractère statistique flou, et plus précisément de caractère qualitatif flou pour lequel nous proposons une interprétation en terme de sous-ensemble. Si la notion de probabilité semble appropriée pour traiter des événements incertains, celle de possibilité est plus indiquée quand les événements sont imprécis.

The definition of a symmetrical difference from the fuzzy implication operators has enabled us to... more The definition of a symmetrical difference from the fuzzy implication operators has enabled us to prove the notion of distance that extends Tchebytchev's distance in the case of fuzzy characters. In the following write up, we are going to show how we can construct a measure of the proximity between two modalities of characters from this distance notion in a fuzzy two dimensional statistical description.

Malaria Journal, 2010

Background: The use of drug combinations, including non-artemisinin-based and artemisinin-based c... more Background: The use of drug combinations, including non-artemisinin-based and artemisinin-based combination therapy (ACT), is a novel strategy that enhances therapeutic efficacy and delays the emergence of multidrugresistant Plasmodium falciparum. Its use is strongly recommended in most sub-Saharan African countries, namely Cameroon, where resistance to chloroquine is widespread and antifolate resistance is emerging. Methods: Studies were conducted in Cameroonian children with acute uncomplicated P. falciparum malaria according to the standard World Health Organization protocol at four sentinel sites between 2003 and 2007. A total of 1,401 children were enrolled, of whom 1,337 were assigned to randomized studies and 64 were included in a single non-randomized study. The proportions of adequate clinical and parasitological response (PCRuncorrected on day 14 and PCR-corrected on day 28) were the primary endpoints to evaluate treatment efficacy on day 14 and day 28. The relative effectiveness of drug combinations was compared by a multi-treatment Bayesian random-effect meta-analysis. Findings: The results based on the meta-analysis suggested that artesunate-amodiaquine (AS-AQ) is as effective as other drugs (artesunate-sulphadoxine-pyrimethamine [AS-SP], artesunate-chlorproguanil-dapsone [AS-CD], artesunate-mefloquine [AS-MQ], dihydroartemisinin-piperaquine [DH-PP], artemether-lumefantrine [AM-LM], amodiaquine, and amodiaquine-sulphadoxine-pyrimethamine [AQ-SP])

Recherche Transports Securite, 1998

In 1996 inrets carried out road haulage pricing surveys in seven countries in three continents, A... more In 1996 inrets carried out road haulage pricing surveys in seven countries in three continents, Africa, South-East Asia and Latin America, in order to gain a clearer picture of the higher cost of transport in Africa. There is a considerable variation in the unit costs of road haulage within a particular country, indeed this variation is greater than the variation between the average price in different countries. In particular, the tonnage which is transported and the distance involved have a major influence on the price per tonne x kilometre. In order to quantify the differences in price which exist between different countries it is therefore necessary to define an indicator which takes account of the main factors which determine prices, other than the country. Varied types of statistical analysis, in particular involving modelling, have been used to indicate how these parameters affect the tariffs of transport in each country and estimate the average price for each country for a particular distance or tonnage. The selected indicators all agree that over long distances road haulage is significantly more expensive in Africa than in Asia. There are differences between the African countries, Cameroon being the most expensive.

Les Cahiers Scientifiques du Transport, 2000

L 'inefficacité des systèmes de transport constitue probablement l 'un des principaux points de ... more L 'inefficacité des systèmes de transport constitue probablement l 'un des principaux points
de blocage au développement des économies africaines. A la fin des années 80, peu avant
la dévaluation du franc CFA, le surcoût de transport pénalisait sérieusement la compétitivité
des produits africains exportés et renchérissait également le prix des produits consommés
sur place, ce qui a conduit notamment la Banque Mondiale à élaborer un Programme de
Politique des transports en Afrique Sub-Saharienne.

JOURNAL OF FUZZY MATHEMATICS, 2002

This paper provides a new way of multi-criteria evaluation. This method is based on the use of f... more This paper provides a new way of multi-criteria evaluation. This method is based on the use of
fuzzy set connectives and fuzzy measures. At the end, we make some comparisons between new
and old ways.

JOURNAL OF FUZZY MATHEMATICS, 2001

In this paper, we have introduced a new notion of logic equivalence based on a parametric family... more In this paper, we have introduced a new notion of logic equivalence based on a
parametric family of fuzzy operators. This equivalence operator has helped us to define a new
dissimilarity index for fuzzy sets. Our index is the fuzzy counterpart of a series of distances
commonly uses in Data Analysis and in particular the cardinal distance of the symmetric
difference. From what follows, we used this dissimilarity to define a new efficiency indicator
for a transport system. This has been made possible with the use of fuzzy uncoupling and its
interpretation in terms of fuzzy logic connectives. We used these new tools on the data from an
investigation that we carried out concerning the transportation of foodstuff in Cameroon.

European Journal of Plant Pathology, Feb 2013

Pod rot causes up to 30 % losses in world cocoa production. In order to predict the risk evolutio... more Pod rot causes up to 30 % losses in world cocoa production. In order to predict the risk evolution of disease, it is important to take into consideration the developmental stage of fruits. In fact, it has been shown that the risk of attack by pod rot depends amongst others on the developmental stage of fruits. We proposed here to estimate the susceptibility at different stages. Susceptibility of fruit to disease was investigated at three fruit developmental stages (cherelle, young pod and adult pod); disease severity was assessed in laboratory conditions, on detached, artificially inoculated fruits, while disease incidence was assessed in the field, under natural inoculum pressure. In both assessment fruits at the cherelle stage were the most susceptible whereas the young and adult fruits were equally susceptible. The vertical position of the fruits on the tree did not influence their susceptibility. Estimates of the fruit susceptibility and of the infectious potential were derived from the severity and incidence measurements, using a model assuming that the number of spores on a fruit follows a Poisson distribution with the mean, the density of spores per fruit as the parameter. The estimated parameter values allowed the evaluation of the probability of attack of a fruit by the disease, which could be implemented in a disease warning system.

Journal of the Royal Statistical Society: Series C (Applied Statistics)

In the estimation of a lifetime distribution from regular interval-censored data with an addition... more In the estimation of a lifetime distribution from regular interval-censored data with an additional censoring variable, we focus on the case where (contrary to the actuarial method) both events (interest and censorship) can occur on a given individual in the same interval and, thus, are observed simultaneously. Specifically, we consider a population where individuals pass through a finite number of successive stages during their growth and are threatened by a disease. First, we estimate the lifetime and time-to-disease distributions in each developmental stage from such censored data. Using data that were recorded on a cohort of individuals followed over a long period of time, we propose a non-parametric, yet continuously differentiable and piecewise quadratic polynomial, estimator for the survival function of each of these distributions. We applied it to estimate, from weekly field observations in Mbankomo (Cameroon), the lifetime and time-to-disease distributions of cocoa fruits in each of their three developmental stages before maturity. It is found that on average a healthy cocoa fruit spends only inline image weeks in its first stage (cherelle), compared with nearly 9 weeks as a young pod and inline image weeks as an adult pod. In a second phase, however, adapting our methodology to competing risks estimation, we observed that, owing to the severe rate of attacks, the fruits' effective lifetime expectancy in farmland is much shorter. Indeed, in that part of Cameroon, the cumulative risk of an attack on cocoa fruits in farmland, especially by pod rot disease, far outweighs their chances of reaching maturity.

Health and system science, 1997

Dans cet article, nous proposons une méthode de saisie et d'analyse des connaissances imprécises.... more Dans cet article, nous proposons une méthode de saisie et d'analyse des connaissances imprécises. Les éléments de la théorie des sous-ensembles flous sont utilisés pour offrir à l'observateur la possibilité d'avoir un choix de réponse discret aux questions qui lui sont posées dans le cadre d'une enquête. Nous proposons par la suite un ensemble d'outils pour analyser ce type de questionnaire. Une enquête tirée de la pédiatrie et mettant en œuvre l'ensemble de ces méthodes est proposée.

IMHOTEP, 2000

La de nition d'une di erence symetrique a partir des operateurs d'implication oue nous a ... more La de nition d'une di erence symetrique a partir des operateurs d'implication

oue nous a permis de mettre en evidence une notion de distance
qui etend celle de Tchebytchev au cas
ou. Nous montrons par la suite
comment on peut, a partir de cette distance, construire une mesure de
la proximite entre deux modalites de caracteres dans une description
statistique
oue a deux dimensions.

Statistics in medicine, Apr 23, 2013

Multiple imputation is commonly used to impute missing covariate in Cox semiparametric regression... more Multiple imputation is commonly used to impute missing covariate in Cox semiparametric regression setting. It is to fill each missing data with more plausible values, via a Gibbs sampling procedure, specifying an imputation model for each missing variable. This imputation method is implemented in several softwares that offer imputation models steered by the shape of the variable to be imputed, but all these imputation models make an assumption of linearity on covariates effect. However, this assumption is not often verified in practice as the covariates can have a nonlinear effect. Such a linear assumption can lead to a misleading conclusion because imputation model should be constructed to reflect the true distributional relationship between the missing values and the observed values. To estimate nonlinear effects of continuous time invariant covariates in imputation model, we propose a method based on B-splines function. To assess the performance of this method, we conducted a simulation study, where we compared the multiple imputation method using Bayesian splines imputation model with multiple imputation using Bayesian linear imputation model in survival analysis setting. We evaluated the proposed method on the motivated data set collected in HIV-infected patients enrolled in an observational cohort study in Senegal, which contains several incomplete variables. We found that our method performs well to estimate hazard ratio compared with the linear imputation methods, when data are missing completely at random, or missing at random. Copyright © 2013 John Wiley & Sons, Ltd.

Recherche - Transports - Sécurité, Sep 1998

In 1996 inrets carried out road haulage pricing surveys in seven countries in three continents, A... more In 1996 inrets carried out road haulage pricing surveys in seven countries in three continents, Africa, South-East Asia and Latin America, in order to gain a clear picture of the higher cost of transport in Africa. There is a considerable variation in the unit costs of road haulage within a particular country, indeed this variation is greater than the variation between the average price in different countries. In particular, the tennage which is transported and the distance involved have a major influence on the price per torine x kilometre. In order to quantify the differences in price which exist between different countries it is therefore necessary to define an indicator which takes account of the main factors which determine prices, other than the country. Varied types of satistical analysis, in particular involving modelling have been used to indicate how these parameter affect the tariffs of transport in each country and estimate the average price for each country for a particular distance or tonnage. The selected indicators all agree that over long distances road haulage is significantly more expensive in Africa than in Asia. There are differences between the African countries, Cameroon being the most expensive.

BMC Medical Research Methodology, 2010

Background: Malaria remains a burden in Sub-Saharan Countries. The strategy proposed by the World... more Background: Malaria remains a burden in Sub-Saharan Countries. The strategy proposed by the World Health Organization (WHO) is to systematically compare the therapeutic efficacy of antimalarial drugs using as primary outcome for efficacy, a four-category ordered criterion. The objective of the present work was to analyze the treatment effects on this primary outcome taking into account both a center-effect and individual covariates. A three-arm, threecentre trial of Amodiaquine (AQ), sulfadoxine-pyrimethamine (SP) and their combination (AQ + SP), conducted by OCEAC-IRD in 2003, in 538 children with uncomplicated Plasmodium falciparum malaria, is used as an illustration. Methods: Analyses were based on ordinal regression methods, assuming an underlying continuous latent variable, using either the proportional odds (PO) or the proportional hazards (PH) models. Different algorithms, corresponding to both frequentist-and bayesian-approaches, were implemented using the freely available softwares R and Winbugs, respectively. The performances of the different methods were evaluated on a simulated data set, and then they were applied on the trial data set. Results: Good coverage probability and type-1 error for the treatment effect were achieved. When the methods were applied on the trial data set, results highlighted a significance decrease of SP efficacy when compared to AQ (PO, odds ratio [OR] 0.14, 95% confidence interval [CI] 0.04-0.57; hazard ratio [HR] 0.605, 95% CI 0.42-0.82), and an equal effectiveness between AQ + SP and AQ (PO, odds ratio [OR] 1.70, 95% confidence interval [CI] 0.25-11.44; hazard ratio [HR] 1.40, 95% CI 0.88-2.18). The body temperature was significantly related to the responses. The patient weights were marginally associated to the clinical response. Conclusion: The proposed analyses, based on usual statistical packages, appeared adapted to take into account the full information contained in the four categorical outcome in malaria trials, as defined by WHO, with the possibility of adjusting on individual and global covariates.

International Journal of Uncertainty, Fuzziness and Knowledge-based Systems, 1997

In this article, we introduce a general concept of fuzzy operators. These operators are then used... more In this article, we introduce a general concept of fuzzy operators. These operators are then used to generalize the possibilistic conditioning formulation proposed by Nguyen [1]. This generalization depends on the relation which exists between this conditioning and the probabilistic t-norm. By using other t-norms, other conditionings are obtained, and their properties are studied. One application of normalized possibilistic conditioning is the measure of the dependency between two fuzzy statistical variables. The measure constructed can be considered as the possibilistic counterpart of mutual information commonly used in statistics.

Malaria Journal, 2010

Background The use of drug combinations, including non-artemisinin-based and artemisinin-based co... more Background The use of drug combinations, including non-artemisinin-based and artemisinin-based combination therapy (ACT), is a novel strategy that enhances therapeutic efficacy and delays the emergence of multidrug-resistant Plasmodium falciparum. Its use is strongly recommended in most sub-Saharan African countries, namely Cameroon, where resistance to chloroquine is widespread and antifolate resistance is emerging. Methods Studies were conducted in Cameroonian children with acute uncomplicated P. falciparum malaria according to the standard World Health Organization protocol at four sentinel sites between 2003 and 2007. A total of 1,401 children were enrolled, of whom 1,337 were assigned to randomized studies and 64 were included in a single non-randomized study. The proportions of adequate clinical and parasitological response (PCR-uncorrected on day 14 and PCR-corrected on day 28) were the primary endpoints to evaluate treatment efficacy on day 14 and day 28. The relative effectiveness of drug combinations was compared by a multi-treatment Bayesian random-effect meta-analysis. Findings The results based on the meta-analysis suggested that artesunate-amodiaquine (AS-AQ) is as effective as other drugs (artesunate-sulphadoxine-pyrimethamine [AS-SP], artesunate-chlorproguanil-dapsone [AS-CD], artesunate-mefloquine [AS-MQ], dihydroartemisinin-piperaquine [DH-PP], artemether-lumefantrine [AM-LM], amodiaquine, and amodiaquine-sulphadoxine-pyrimethamine [AQ-SP]). AM-LM appeared to be the most effective with no treatment failure due to recrudescence, closely followed by DH-PP. Conclusion Although AM-LM requires six doses, rather than three doses for other artemisinin-based combinations, it has potential advantages over other forms of ACT. Further studies are needed to evaluate the clinical efficacy and tolerance of these combinations in different epidemiological context.

BMC Public Health, 2010

Background: Coinfection with hepatitis B virus (HBV) or hepatitis C virus (HCV) in HIV-infected p... more Background: Coinfection with hepatitis B virus (HBV) or hepatitis C virus (HCV) in HIV-infected patients receiving a commonly used nevirapine-based antiretroviral therapy is a major concern for African clinicians owing to its high prevalence, the infrequent testing and treatment of viral hepatitis, and the impact of liver disease on the tolerability and effectiveness of anti-HIV treatment. We compared the hepatotoxicity and the immunological, virological and clinical effectiveness of a nevirapine-based antiretroviral therapy between patients infected with HIV only and patients coinfected with hepatitis B or C virus in Cameroon. Methods: A retrospective cohort study was conducted among HIV-1-infected patients. Plasma HBV DNA and HCV RNA were tested in positive or indeterminate samples for HBsAg or HCV antibodies, respectively. All patients received nevirapine and lamivudine plus stavudine or zidovudine. Results: Of 169 HIV-1-infected patients with a median baseline CD4 count of 135 cells/mm 3 (interquartile range [IQR] 67-218), 21% were coinfected with HBV or HCV. In coinfected patients, the median viral load was 2.47 × 10 7 IU/mL for HBV (IQR 3680-1.59 × 10 8 ) and 928 000 IU/mL for HCV (IQR 178 400-2.06 × 10 6 ). Multivariate analyses showed that the risk of hepatotoxicity was 2-fold higher in coinfected patients (p < 0.01). The response to antiretroviral therapy was however comparable between monoinfected and coinfected patients in terms of CD4 cell count increase (p = 0.8), HIV-1 viral load below 400 copies/mL (p = 0.9), death (p = 0.3) and death or new AIDS-defining event (p = 0.1). Nevirapine was replaced by a protease inhibitor in 4 patients owing to hepatotoxicity. Conclusion: This study suggests that the nevirapine-based antiretroviral therapy could be used safely as first-line treatment in patients with low CD4 cell count in Africa despite frequent coinfections with HBV or HCV and infrequent testing of these infections. Although testing for HBV and HCV should be systematically performed before initiating antiretroviral therapy, transaminases elevations at baseline or during treatment should be a decisive argument for testing when hepatitis status is unknown.