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Use of cumulative incidence of novel influenza A/H1N1 in foreign travelers to estimate lower bounds on cumulative incidence in Mexico

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Lipsitch, Marc, Lajous, Martin, O'Hagan, Justin J., Cohen, Ted, Miller, Joel C., Goldstein, Edward, Danon, Leon, Wallinga, Jacco, Riley, Steven, Dowell, Scott F., Reed, Carrie and McCarron, Meg. (2009) Use of cumulative incidence of novel influenza A/H1N1 in foreign travelers to estimate lower bounds on cumulative incidence in Mexico. PL o S One, Vol.4 (No.9). ISSN 1932-6203

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Official URL: http://dx.doi.org/10.1371/journal.pone.0006895

Abstract

Background: An accurate estimate of the total number of cases and severity of illness of an emerging infectious disease is
required both to define the burden of the epidemic and to determine the severity of disease. When a novel pathogen first
appears, affected individuals with severe symptoms are more likely to be diagnosed. Accordingly, the total number of cases
will be underestimated and disease severity overestimated. This problem is manifest in the current epidemic of novel
influenza A/H1N1.
Methods and Results: We used a simple approach to leverage measures of incident influenza A/H1N1 among a relatively
small and well observed group of US, UK, Spanish and Canadian travelers who had visited Mexico to estimate the incidence
among a much larger and less well surveyed population of Mexican residents. We estimate that a minimum of 113,000 to
375,000 cases of novel influenza A/H1N1 have occurred in Mexicans during the month of April, 2009. Such an estimate
serves as a lower bound because it does not account for underreporting of cases in travelers or for nonrandom mixing
between Mexican residents and visitors, which together could increase the estimates by more than an order of magnitude.
Conclusions: We find that the number of cases in Mexican residents may exceed the number of confirmed cases by two to
three orders of magnitude. While the extent of disease spread is greater than previously appreciated, our estimate suggests
that severe disease is uncommon since the total number of cases is likely to be much larger than those of confirmed cases.

Item Type:

Journal Article

Subjects:

R Medicine > RA Public aspects of medicine

Divisions:

Faculty of Science > Life Sciences (2010- ) > Biological Sciences ( -2010)

Library of Congress Subject Headings (LCSH):

H1N1 influenza -- Transmission -- Mexico, H1N1 influenza -- Epidemiology, Travelers -- Mexico

Journal or Publication Title:

PL o S One

Publisher:

Public Library of Science

ISSN:

1932-6203

Official Date:

9 September 2009

Dates:

Date	Event
9 September 2009	Published

Volume:

Vol.4

Number:

No.9

Identification Number:

10.1371/journal.pone.0006895

Status:

Peer Reviewed

Access rights to Published version:

Open Access

Funder:

National Institutes of Health (U.S.) (NIH), Consejo Nacional de Ciencia y Tecnología (Mexico) [Mexican Council for Science and Technology] (CONACYT), Mexico. Secretaría de Salud [Ministry of Health], Harvard University. Dept. of Epidemiology, United States. Dept. of Homeland Security. Science and Technology Directorate, Medical Research Council (Great Britain) (MRC), Hong Kong

Grant number:

5U01GM076497 (NIH), NIH R01 TW008246-01 (NIH)

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