Comparative Epidemiology of Pandemic and Seasonal Influenza A in Households

Abstract

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.

Estimating age‐specific cumulative incidence for the 2009 influenza pandemic: a meta‐analysis of A(H1N1)pdm09 serological studies from 19 countries

“…This may be because our study includes a number of additional middle and low countries who conducted serologic studies because this analysis was published and because we excluded studies which focused on specialized populations17). Additionally, the age‐specific trends we found in our cumulative incidence results are consistent with studies which measured cumulative incidence as a fourfold increase in titers among paired sera36, 42, 57 and similar to studies which measured age‐specific secondary attack rates using RT‐PCR 58, 59…”

Swine Outbreak of Pandemic Influenza A Virus on a Canadian Research Farm Supports Human-to-Swine Transmission

“…We performed throat swabs to comply with a public health directive explicitly forbidding nasopharyngeal swabbing and aspirates in community settings [31]. Although the use of throat swab specimens for testing for the presence of virus may have contributed to the lack of positive RT-PCR results, it is more likely that humans with ILI were no longer shedding virus 2 weeks after their illness, when the swab specimens were taken [32]. Secondly, some individuals may have been incorrectly classified as positive for pH1N1 on the basis of cross-reactive serological test results.…”

Effect of short-term school closures on the H1N1 pandemic in Japan: a comparative case study

“…Our findings also showed that the effects of closure were related to the duration of the closure. Because an epidemic may be influenced by several factors, such as transmission within households [22,28], the severity or transmissibility of the strain of influenza [15] or weather [18], further detailed investigations that include these factors are required to clarify the effects of school closure.…”