Influenza: H1N1 Goes to School

Abstract

A key determinant of the success of influenza containment is the transmission rate of the novel strain. C. Fraser et al. [“Pandemic potential of a strain of influenza A (H1N1): Early findings,” Reports, 19 June, p. [1557][1]] estimated the basic reproduction number ( R ) of the Mexican outbreak of influenza A (H1N1) to be in the range of 1.2 to 1.6. The value of R is a key measure of transmissibility and estimates the number of secondary cases in a completely susceptible population. Their findings were comparable to lower estimates for the 1918 pandemic, where R ranged from 2 to 3 ([ 1 ][2]). To further investigate the transmissibility of this novel virus, we conducted a secondary analysis of the largest reported cluster of influenza A (H1N1) ([ 2 ][3]). We used survey data from students of the St. Francis Preparatory School outbreak in the United States to calculate the effective reproduction number ( R ) in a school-based setting. R is the average number of secondary cases generated by an infectious case during an epidemic and is usually comparable to R . This survey collected data on self-reported fever and either cough or sore throat between 8 and 28 April 2009. We used the method proposed by Vynncky et al. ([ 3 ][4]) to calculate R from the growth rate of the epidemic. We based our parameter assumptions on estimates for seasonal influenza commonly reported in the literature, because such values are not yet available for H1N1. The parameters were as follows: incubation period of 2 days; infectious period of 3 days; and a calculated serial interval of 5 days. The serial interval is the time between the onset of symptoms for first and second generation cases. Using daily data from the outbreak growth phase, we calculated R to be 2.69 [95% confidence interval: 2.20 to 3.22; degrees of freedom (df) = 13]. Increasing the estimated infectious period to 5 days results in an R of 3.45 (95% confidence interval: 2.74 to 4.28; df = 13). The confidence interval for R was derived from a Monte Carlo simulation based on the uncertainty of the slope estimate. Estimates of R were relatively insensitive to the use of data from the growth phase or entire outbreak. Our calculated R is specific to this school setting and, with the increased transmission potential of a close-contact setting such as a school, is likely to be higher than transmission rates in the community-wide Mexican outbreak. The use of parameters estimated from seasonal influenza will need confirmation for the 2009 influenza A H1N1 virus. Our analysis supports the findings from Fraser et al. that this H1N1 virus has a transmission rate comparable to the lower R estimates of 2 for the 1918 pandemic ([ 1 ][2]). 1. [↵][5] 1. G. Chowell, 2. H. Nishiura, 3. L. Bettencourt , J. R. Soc. Interface 4, 155 (2007). [OpenUrl][6][Abstract/FREE Full Text][7] 2. [↵][8] 1. T. R. Frieden , Commissioner, “St. Francis Prep Update: Swine Flu Outbreak” (New York City Department of Health and Mental Hygiene, New York, 2009); ([www.nyc.gov/html/doh/downloads/pdf/cd/h1n1\_stfrancis\_survey.pdf][9]). 3. [↵][10] 1. E. Vynncky, 2. A. Trindall, 3. P. Mangtani , Int. J. Epidemiol. 36, 881 (2007). [OpenUrl][11][Abstract/FREE Full Text][12] [1]: /lookup/doi/10.1126/science.1176062 [2]: #ref-1 [3]: #ref-2 [4]: #ref-3 [5]: #xref-ref-1-1 View reference 1 in text [6]: {openurl}?query=rft.jtitle%253DJournal%2Bof%2BThe%2BRoyal%2BSociety%2BInterface%26rft.stitle%253DJ%2BR%2BSoc%2BInterface%26rft.issn%253D1742-5662%26rft.aulast%253DChowell%26rft.auinit1%253DG.%26rft.volume%253D4%26rft.issue%253D12%26rft.spage%253D155%26rft.epage%253D166%26rft.atitle%253DComparative%2Bestimation%2Bof%2Bthe%2Breproduction%2Bnumber%2Bfor%2Bpandemic%2Binfluenza%2Bfrom%2Bdaily%2Bcase%2Bnotification%2Bdata%26rft_id%253Dinfo%253Adoi%252F10.1098%252Frsif.2006.0161%26rft_id%253Dinfo%253Apmid%252F17254982%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [7]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6MTI6InJveWludGVyZmFjZSI7czo1OiJyZXNpZCI7czo4OiI0LzEyLzE1NSI7czo0OiJhdG9tIjtzOjI1OiIvc2NpLzMyNS81OTQ0LzEwNzEuMi5hdG9tIjt9czo4OiJmcmFnbWVudCI7czowOiIiO30= [8]: #xref-ref-2-1 View reference 2 in text [9]: http://www.nyc.gov/html/doh/downloads/pdf/cd/h1n1_stfrancis_survey.pdf [10]: #xref-ref-3-1 View reference 3 in text [11]: {openurl}?query=rft.jtitle%253DInt.%2BJ.%2BEpidemiol.%26rft_id%253Dinfo%253Adoi%252F10.1093%252Fije%252Fdym071%26rft_id%253Dinfo%253Apmid%252F17517812%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [12]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6ODoiaW50amVwaWQiO3M6NToicmVzaWQiO3M6ODoiMzYvNC84ODEiO3M6NDoiYXRvbSI7czoyNToiL3NjaS8zMjUvNTk0NC8xMDcxLjIuYXRvbSI7fXM6ODoiZnJhZ21lbnQiO3M6MDoiIjt9