BACKGROUND There are few data on the comparative epidemiology and virology of the pandemic 2009 influenza A (H1N1) virus and cocirculating seasonal influenza A viruses in community settings. METHODS We recruited 348 index patients with acute respiratory illness from 14 outpatient clinics in Hong Kong in July and August 2009. We then prospectively followed household members of 99 patients who tested positive for influenza A virus on rapid diagnostic testing. We collected nasal and throat swabs from all household members at three home visits within 7 days for testing by means of quantitative reverse-transcriptase–polymerase-chain-reaction (RT-PCR) assay and viral culture. Using hemagglutination-inhibition and viral-neutralization assays, we tested baseline and convalescent serum samples from a subgroup of patients for antibody responses to the pandemic and seasonal influenza A viruses. RESULTS Secondary attack rates (as confirmed on RT-PCR assay) among household contacts of index patients were similar for the pandemic influenza virus (8%; 95% confidence interval [CI], 3 to 14) and seasonal influenza viruses (9%; 95% CI, 5 to 15). The patterns of viral shedding and the course of illness among index patients were also similar for the pandemic and seasonal influenza viruses. In a subgroup of patients for whom baseline and convalescent serum samples were available, 36% of household contacts who had serologic evidence of pandemic influenza virus infection did not shed detectable virus or report illness. CONCLUSIONS Pandemic 2009 H1N1 virus has characteristics that are broadly similar to those of seasonal influenza A viruses in terms of rates of viral shedding, clinical illness, and transmissibility in the household setting.
Background Serial cross-sectional data on antibody levels to 2009 pandemic influenza A (H1N1) virus from a population can be used to estimate the infection attack rates and immunity against future infection in the community. Methods Between April and December 2009, we obtained 12,217 serum specimens from blood donors (16–59 yo), 2,520 from hospital outpatients (5–59yo), and 917 from subjects of a community pediatric cohort study (5–14yo). We estimated infection attack rates by comparing the proportions of specimens with antibody titers ≥1:40 by viral microneutralization before and after the first wave of the pandemic. Estimates were validated using paired sera from 324 individuals that spanned the first wave. Combining these estimates with epidemiologic surveillance data, we calculated the proportion of infections that led to hospitalization, intensive care admission, and death. Results We found that 3.3% and 14% of 5–59 yo had antibody titers ≥1:40 before and after the first wave. The overall attack rate was 10.7% with the following age-stratification: 43.4% in 5–14 yo, 15.8% in 15–19 yo, 11.8% in 20–29 yo, and 4–4.6% in 30–59 yo. Case-hospitalization rates were 0.47%–0.87% among 5–59 yo. Case-ICU and case-fatality rates increased from 7.9 and 0.4 per 100,000 infections in 5–14 yo to 75 and 26.5 per 100,000 infections in 50–59 yo. Conclusions Almost half of all school-children in Hong Kong were infected during the first wave. Compared to school-children aged 5–14, older adults aged 50–59 had 9.5 and 66 times higher risk of ICU admission and death if infected.
ClinicalTrials.gov number NCT00792051 .
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.