Pandemic Influenza due to pH1N1/2009 virus: estimation of infection burden in Reunion Island through a prospective serosurvey, Austral winter 2009

Dellagi, Koussay, Rollot, Olivier, Temmam, Sarah, Salez, Nicolas, Guernier, Vanina, Pascalis, Hervé, Gérardin, Patrick, Fianu, Adrian, Lapidus, Nathanael, Naty, Nadège, Tortosa, Pablo, Boussaïd, Karim, Jaffar-Banjee, Marie-Christine, Filleul, Laurent, Flahault, Antoine, Carrat, Fabrice, Favier, Francois, and de Lamballerie, Xavier (2011) Pandemic Influenza due to pH1N1/2009 virus: estimation of infection burden in Reunion Island through a prospective serosurvey, Austral winter 2009. PLoS ONE, 6 (9). e25738. pp. 1-10.

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Background: To date, there is little information that reflects the true extent of spread of the pH1N1/2009v influenza pandemic at the community level as infection often results in mild or no clinical symptoms. This study aimed at assessing through a prospective study, the attack rate of pH1N1/2009 virus in Reunion Island and risk factors of infection, during the 2009 season.

Methodology/Principal Findings: A serosurvey was conducted during the 2009 austral winter, in the frame of a prospective population study. Pairs of sera were collected from 1687 individuals belonging to 772 households, during and after passage of the pandemic wave. Antibodies to pH1N1/2009v were titered using the hemagglutination inhibition assay (HIA) with titers ≥1/40 being considered positive. Seroprevalence during the first two weeks of detection of pH1N1/2009v in Reunion Island was 29.8% in people under 20 years of age, 35.6% in adults (20–59 years) and 73.3% in the elderly (≥60 years) (P<0.0001). Baseline corrected cumulative incidence rates, were 42.9%, 13.9% and 0% in these age groups respectively (P<0.0001). A significant decline in antibody titers occurred soon after the passage of the epidemic wave. Seroconversion rates to pH1N1/2009 correlated negatively with age: 63.2%, 39.4% and 16.7%, in each age group respectively (P<0.0001). Seroconversion occurred in 65.2% of individuals who were seronegative at inclusion compared to 6.8% in those who were initially seropositive.

Conclusions: Seroincidence of pH1N1/2009v infection was three times that estimated from clinical surveillance, indicating that almost two thirds of infections occurring at the community level have escaped medical detection. People under 20 years of age were the most affected group. Pre-epidemic titers ≥1/40 prevented seroconversion and are likely protective against infection. A concern was raised about the long term stability of the antibody responses.

Item ID: 44716
Item Type: Article (Research - C1)
ISSN: 1932-6203
Additional Information:

© 2011 Dellagi et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funders: Contrat Programme Etat/Region, European Regional Development Fund, INSERM/IMMI, Centre de Recherche et de Veille sur les Maladies Emergentes dans l'Océan Indien
Date Deposited: 02 Aug 2016 00:35
FoR Codes: 11 MEDICAL AND HEALTH SCIENCES > 1117 Public Health and Health Services > 111706 Epidemiology @ 100%
SEO Codes: 92 HEALTH > 9201 Clinical Health (Organs, Diseases and Abnormal Conditions) > 920109 Infectious Diseases @ 100%
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