Monitoring the impact of influenza by age: emergency department fever and respiratory complaint surveillance in New York City - PubMed (original) (raw)
Monitoring the impact of influenza by age: emergency department fever and respiratory complaint surveillance in New York City
Donald R Olson et al. PLoS Med. 2007 Aug.
Abstract
Background: The importance of understanding age when estimating the impact of influenza on hospitalizations and deaths has been well described, yet existing surveillance systems have not made adequate use of age-specific data. Monitoring influenza-related morbidity using electronic health data may provide timely and detailed insight into the age-specific course, impact and epidemiology of seasonal drift and reassortment epidemic viruses. The purpose of this study was to evaluate the use of emergency department (ED) chief complaint data for measuring influenza-attributable morbidity by age and by predominant circulating virus.
Methods and findings: We analyzed electronically reported ED fever and respiratory chief complaint and viral surveillance data in New York City (NYC) during the 2001-2002 through 2005-2006 influenza seasons, and inferred dominant circulating viruses from national surveillance reports. We estimated influenza-attributable impact as observed visits in excess of a model-predicted baseline during influenza periods, and epidemic timing by threshold and cross correlation. We found excess fever and respiratory ED visits occurred predominantly among school-aged children (8.5 excess ED visits per 1,000 children aged 5-17 y) with little or no impact on adults during the early-2002 B/Victoria-lineage epidemic; increased fever and respiratory ED visits among children younger than 5 y during respiratory syncytial virus-predominant periods preceding epidemic influenza; and excess ED visits across all ages during the 2003-2004 (9.2 excess visits per 1,000 population) and 2004-2005 (5.2 excess visits per 1,000 population) A/H3N2 Fujian-lineage epidemics, with the relative impact shifted within and between seasons from younger to older ages. During each influenza epidemic period in the study, ED visits were increased among school-aged children, and each epidemic peaked among school-aged children before other impacted age groups.
Conclusions: Influenza-related morbidity in NYC was highly age- and strain-specific. The impact of reemerging B/Victoria-lineage influenza was focused primarily on school-aged children born since the virus was last widespread in the US, while epidemic A/Fujian-lineage influenza affected all age groups, consistent with a novel antigenic variant. The correspondence between predominant circulating viruses and excess ED visits, hospitalizations, and deaths shows that excess fever and respiratory ED visits provide a reliable surrogate measure of incident influenza-attributable morbidity. The highly age-specific impact of influenza by subtype and strain suggests that greater age detail be incorporated into ongoing surveillance. Influenza morbidity surveillance using electronic data currently available in many jurisdictions can provide timely and representative information about the age-specific epidemiology of circulating influenza viruses.
Conflict of interest statement
Competing Interests: The authors have declared that no competing interests exist.
Figures
Figure 1. Weekly Influenza Isolates and ED Fever and Respiratory and ILI Visits in New York City during the 2001–2002 to 2005–2006 Seasons
Dates are CDC year and week ending Saturday. Top graph, isolates by influenza type are from WHO collaborating laboratories, with subtype and strain designation based on predominant regional and national antigenic lineage: A/H3-SY, predominant circulating A(H3N2) Sydney-lineage viruses; B/VI, predominant circulating B/Victoria-lineage; A/H1, either A(H1N1) New Caledonia- or A(H1N2) Wisconsin-lineage; A/H3-FU, A(H3N2) Fujian-lineage; B/YA, B/Yamagata-lineage; and A/H3-CA, A(H3N2) California-lineage. Middle and bottom graphs, observed fever and respiratory syndrome (middle) and ILI syndrome (bottom) ED visits are shown as black lines, and seasonally expected Serfling baseline visits as red lines. Dashed lines represent epidemic thresholds as model estimates plus two standard deviations. Shaded areas represent estimated influenza-attributable excess ED visits: blue areas correspond to periods of increasing and dominant influenza A circulation and red areas to influenza B. Vertical lines indicate the first week of continuous influenza isolate reporting each season.
Figure 2. Weekly Age-Specific Fever and Respiratory ED Visits in New York City during the 2001–2002 to 2005–2006 Seasons
Observed fever and respiratory ED visits by age group are shown as black lines, and seasonally expected Serfling baseline visits are as red lines. Dashed lines represent model estimates plus two standard deviations. Shaded areas represent influenza-attributable excess ED visits by type A (blue) or B (red). Vertical lines indicate the first week of continuous influenza isolate reporting. Codes in top graph: A/H3-SY, influenza A(H3N2) Sydney; B/VI, influenza B/Victoria; A/H1, either A(H1N1) New Caledonia or A(H1N2) Wisconsin; A/H3-FU, influenza A(H3N2) Fujian; B/YA, influenza B/Yamagata; and A/H3-CA, influenza A(H3N2) California.
Figure 3. Weekly P&I Hospitalizations and All-Cause and P&I Deaths in New York City
Observed P&I hospitalizations by age group from 1998–1999 to 2004–2005, and deaths for all ages from 1998–1999 to 2003–2004, are shown as black lines. Seasonally expected Serfling baseline levels are shown as red lines, and two-standard-deviation thresholds are shown as dashed lines. Catastrophic event deaths were removed from the data, and heat-wave period deaths were censored from the Serfling analysis. Observed P&I deaths during the 1999–2000 season were low due to a changeover from ICD-9 to ICD-10 coding. Codes in top graph: A/H3-SY, influenza A(H3N2) Sydney; B/VI, influenza B/Victoria; A/H1, either A(H1N1) New Caledonia or A(H1N2) Wisconsin; A/H3-FU, influenza A(H3N2) Fujian; B/YA, influenza B/Yamagata; and A/H3-CA, influenza A(H3N2) California.
Figure 4. Epidemic Weekly Lead or Lag Cross-Correlation during the 2003–2004 Influenza A/Fujian Season in New York City
Excess fever and respiratory ED visits and P&I hospitalizations and deaths were correlated against influenza isolates during the 33 wk centered on peak isolates. Top, maximum cross-correlation values for ED visits and hospitalizations coincided with influenza isolates (no lag) with ED visits leading hospitalizations, by less than 1 wk. Maximum correlation values for P&I deaths lagged isolates by 2 wk. Middle, maximum correlation values for 2–4 y, 5–12 y, and 13–17 y ED visits led isolates by 1 wk, < 2 y, 18–39 y, and 40–64 y visits had no lag, and ≥ 65 y visits lagged isolates by 1 wk. Bottom, maximum cross-correlation values for < 65 y P&I hospitalizations had no lag, for ≥ 65 y hospitalizations and < 65 y P&I deaths had a 1 wk lag, and for ≥ 65 y P&I deaths had a 3 wk lag.
Figure 5. Observed Fever and Respiratory ED Visit Surface Plots by Age Group in New York City during the 2001–2002 to 2005–2006 Influenza Seasons
Each season is shown from early September through mid-June by CDC week and year. Weeks of predominant influenza A (blue bar) or B (red bar) isolate surveillance during the study period, retrospectively identified predominant RSV hospitalizations through 2005 (gray bar), and dominant tree pollen periods for 2005 and 2006 (green bar) are shown above each season. Weekly ED visits by age group were detrended and normalized: age-specific intensity is shown as a color gradient interpolated between data points, with observed visits ranging from 2 to >4 times mean noninfluenza levels during peak epidemic weeks, and 0.25 to 1.25 during nonepidemic periods. Visits were increased across all age groups during periods of influenza A/H3N2 predominance, and were most markedly increased during the 2003–2004 and 2004–2005 A/Fujian-lineage epidemics. Visit increases during periods of influenza A/H1 and B predominance impacted preschool (2–4 y) and school-aged (5–17 y) children, and were most dramatically elevated during the B/Victoria-lineage reemergence in early 2002. The autumn and early-winter predominance of RSV preceded influenza in 2001, 2002, and 2005, and coincided with increased visits in the < 2 y and 2–4 y age groups. Visits were notably increased among school-aged children and working-aged adults during the dominant tree pollen period in 2006. RSV hospitalization data were not available for 2006 (*), and viral influenza surveillance reporting was incomplete during weeks 12 to 16, 2006 (*).
References
- Glezen WP. Emerging Infections: Pandemic influenza. Epidemiol Rev. 1996;18:64–76. - PubMed
- Palese P. Influenza: Old and new threats. Nat Med. 2004;10:S82–87. - PubMed
- US Department of Health and Human Services. HHS pandemic influenza preparedness plan. 2006. Available: http://www.hhs.gov/pandemicflu/plan/. Accessed 16 April 2007.
- CDC. CDC flu activity. 2007. Available: http://www.cdc.gov/flu/weekly/fluactivity.htm. Accessed 16 April 2007.
Publication types
MeSH terms
LinkOut - more resources
Full Text Sources
Other Literature Sources
Medical