The Novel H7N9 Influenza A Virus: Its Present Impact and Indeterminate Future (original) (raw)
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Epidemiology of Human Infections with Avian Influenza A(H7N9) Virus in China
New England Journal of Medicine, 2014
Background The first identified cases of avian influenza A(H7N9) virus infection in humans occurred in China during February and March 2013. We analyzed data obtained from field investigations to describe the epidemiologic characteristics of H7N9 cases in China identified as of December 1, 2013. Methods Field investigations were conducted for each confirmed case of H7N9 virus infection. A patient was considered to have a confirmed case if the presence of the H7N9 virus was verified by means of real-time reverse-transcriptase-polymerase-chainreaction assay (RT-PCR), viral isolation, or serologic testing. Information on demographic characteristics, exposure history, and illness timelines was obtained from patients with confirmed cases. Close contacts were monitored for 7 days for symptoms of illness. Throat swabs were obtained from contacts in whom symptoms developed and were tested for the presence of the H7N9 virus by means of real-time RT-PCR. Results Among 139 persons with confirmed H7N9 virus infection, the median age was 61 years (range, 2 to 91), 71% were male, and 73% were urban residents. Confirmed cases occurred in 12 areas of China. Nine persons were poultry workers, and of 131 persons with available data, 82% had a history of exposure to live animals, including chickens (82%). A total of 137 persons (99%) were hospitalized, 125 (90%) had pneumonia or respiratory failure, and 65 of 103 with available data (63%) were admitted to an intensive care unit. A total of 47 persons (34%) died in the hospital after a median duration of illness of 21 days, 88 were discharged from the hospital, and 2 remain hospitalized in critical condition; 2 patients were not admitted to a hospital. In four family clusters, humanto-human transmission of H7N9 virus could not be ruled out. Excluding secondary cases in clusters, 2675 close contacts of case patients completed the monitoring period; respiratory symptoms developed in 28 of them (1%); all tested negative for H7N9 virus. Conclusions Most persons with confirmed H7N9 virus infection had severe lower respiratory tract illness, were epidemiologically unrelated, and had a history of recent exposure to poultry. However, limited, nonsustained human-to-human H7N9 virus transmission could not be ruled out in four families.
The Lancet, 2013
Background The novel infl uenza A H7N9 virus emerged recently in mainland China, whereas the infl uenza A H5N1 virus has infected people in China since 2003. Both infections are thought to be mainly zoonotic. We aimed to compare the epidemiological characteristics of the complete series of laboratory-confi rmed cases of both viruses in mainland China so far. Methods An integrated database was constructed with information about demographic, epidemiological, and clinical variables of laboratory-confi rmed cases of H7N9 (130 patients) and H5N1 (43 patients) that were reported to the Chinese Centre for Disease Control and Prevention until May 24, 2013. We described disease occurrence by age, sex, and geography, and estimated key epidemiological variables. We used survival analysis techniques to estimate the following distributions: infection to onset, onset to admission, onset to laboratory confi rmation, admission to death, and admission to discharge. Findings The median age of the 130 individuals with confi rmed infection with H7N9 was 62 years and of the 43 with H5N1 was 26 years. In urban areas, 74% of cases of both viruses were in men, whereas in rural areas the proportions of the viruses in men were 62% for H7N9 and 33% for H5N1. 75% of patients infected with H7N9 and 71% of those with H5N1 reported recent exposure to poultry. The mean incubation period of H7N9 was 3•1 days and of H5N1 was 3•3 days. On average, 21 contacts were traced for each case of H7N9 in urban areas and 18 in rural areas, compared with 90 and 63 for H5N1. The fatality risk on admission to hospital was 36% (95% CI 26-45) for H7N9 and 70% (56-83%) for H5N1. Interpretation The sex ratios in urban compared with rural cases are consistent with exposure to poultry driving the risk of infection-a higher risk in men was only recorded in urban areas but not in rural areas, and the increased risk for men was of a similar magnitude for H7N9 and H5N1. However, the diff erence in susceptibility to serious illness with the two diff erent viruses remains unexplained, since most cases of H7N9 were in older adults whereas most cases of H5N1 were in younger people. A limitation of our study is that we compared laboratory-confi rmed cases of H7N9 and H5N1 infection, and some infections might not have been ascertained.
Clusters of Human Infections With Avian Influenza A(H7N9) Virus in China, March 2013 to June 2015
The Journal of Infectious Diseases
Multiple clusters of human infections with novel avian influenza A(H7N9) virus have occurred since the virus was first identified in spring 2013. However, in many situations it is unclear whether these clusters result from person-to-person transmission or exposure to a common infectious source. We analyzed the possibility of person-to-person transmission in each cluster and developed a framework to assess the likelihood that person-to-person transmission had occurred. We described 21 clusters with 22 infected contact cases that were identified by the Chinese Center for Disease Control and Prevention from March 2013 through June 2015. Based on detailed epidemiological information and the timing of the contact case patients' exposures to infected persons and to poultry during their potential incubation period, we graded the likelihood of person-to-person transmission as probable, possible, or unlikely. We found that person-to-person transmission probably occurred 12 times and possibly occurred 4 times; it was unlikely in 6 clusters. Probable nosocomial transmission is likely to have occurred in 2 clusters. Limited person-to-person transmission is likely to have occurred on multiple occasions since the H7N9 virus was first identified. However, these transmission events represented a small fraction of all identified cases of H7N9 human infection, and sustained person-to-person transmission was not documented. Keywords. H7N9 virus; avian influenza; China. METHODS After Chinese public health authorities were notified of a possible human H7N9 case, national, provincial, and local public health authorities conducted an investigation. The Chinese Center for Disease Control and Prevention received information
Monitoring Avian Influenza A(H7N9) Virus through National Influenza-like Illness Surveillance, China
Emerging Infectious Diseases, 2013
In China during March 4-April 28, 2013, avian influenza A(H7N9) virus testing was performed on 20,739 specimens from patients with influenza-like illness in 10 provinces with confirmed human cases: 6 (0.03%) were positive, and increased numbers of unsubtypeable influenza-positive specimens were not seen. Careful monitoring and rapid characterization of influenza A(H7N9) and other influenza viruses remain critical. A s of April 28, 2013, a total of 125 cases of avian influenza A(H7N9) virus infection and 24 related deaths were confirmed in humans in 8 provinces and 2 municipalities (hereafter called affected provinces/municipalities) of mainland China (1). The median age of patients was 63 years; most were male and had a history of exposure to live poultry (2). The first confirmed case was reported on March 31. On April 3, the Chinese Center for Disease Control and Prevention (China CDC) distributed primers and probes specific for avian influenza A(H7N9) virus to all national influenza surveillance network laboratories in China. To better understand the epidemiology, geographic spread, and clinical spectrum of this virus in China, we describe the Chinese National Influenza-Like Illness Surveillance Network (CNISN) and analyze data collected since March 4, 2013.
Scientific Reports, 2017
Inapparent avian exposure was suspected for the sporadic infection of avian influenza A(H7N9) occurring in China. This type of exposure is usually unnoticed and difficult to model and measure. Infected poultry with avian influenza H7N9 virus typically remains asymptomatic, which may facilitate infection through inapparent poultry/bird exposure, especially in a country with widespread practice of backyard poultry. The present study proposed a novel approach that integrated ecological and casecontrol methods to quantify the risk of inapparent avian exposure on human H7N9 infection. Significant associations of the infection with chicken and goose densities, but not with duck density, were identified after adjusting for spatial clustering effects of the H7N9 cases across multiple geographic scales of neighborhood, community, district and city levels. These exposure risks varied geographically in association with proximity to rivers and lakes that were also proxies for inapparent exposure to avian-related environment. Males, elderly people, and farmers were high-risk subgroups for the virus infection. These findings enable health officials to target educational programs and awareness training in specific locations to reduce the risks of inapparent exposure. Avian influenza A(H7N9) virus, detected strictly in birds in the past, finally spread to humans and animals in China in February/March of 2013 1. The virus is low pathogenic for avian hosts, resulting in asymptomatic or mild avian diseases 2. This asymptomatic infection of poultry may cause a 'silent' poultry-to-human transmission through direct contact with or exposure to seemingly healthy but infected birds 3. The number of laboratory-confirmed H7N9 cases in China reached 511 within a span of just 1.5 months; with 209 deaths from 12 provinces and two municipalities 4. Although incorrectly lumped with other avian influenza viruses at the outset, the H7N9 virus originating from southeastern coast of China continued its spread to other regions 5,6. It was soon affirmed that the H7N9 virus is a global issue in public health 7 because the virus has obtained strong abilities of jumping from its avian origins to mammals to cause severe illnesses and even deaths in human. Direct poultry contact and exposures to poultry in live-poultry markets (LPMs) are potential sources of H7N9 infection 8-11. LPMs have been reported as a main source of H7N9 transmission by way of human-poultry contact and avian-related environmental exposures 12-14. The closures of LPMs appeared to decrease the risks of H7N9 infection in many Chinese cities such as Shanghai, Hangzhou, Huzhou and Nanjing 15. However, the intervention was not always effective as demonstrated in Hangzhou and other counties of the Zhejiang province where new cases occurred after LPMs had been permanently closed in the winters of 2014 and 2015 16-19. The H7N9 virus continued to spread not only around LPMs, backyards, and small-scale poultry farms but also in natural environmental settings that were more difficult to detect 20. Inapparent avian exposure might have contributed to the sporadic re-emergence of the H7N9 infection in Hangzhou even though all the LPMs were permanently shut down in this city 21,22 .