Estimating Chikungunya prevalence in La Reunion Island outbreak by serosurveys: two methods for two critical times of the epidemic
Chikungunya virus (CHIKV) caused a major two-wave seventeen-month-long outbreak in La Reunion Island in 2005-2006. The aim of this study was to refine clinical estimates provided by a regional surveillance-system using a two-stage serological assessment as gold standard.
Methods: Two serosurveys were implemented: first, a rapid survey using stored sera of pregnant women, in order to assess the attack rate at the epidemic upsurge (s1, February 2006; n=888); second, a population-based survey among a random sample of the community, to assess the herd immunity in the post-epidemic era (s2, October 2006; n=2442).
Sera were screened for anti-CHIKV specific antibodies (IgM and IgG in s1, IgG only in s2) using enzyme-linked immunosorbent assays. Seroprevalence rates were compared to clinical estimates of attack rates.
Results: In s1, 18.2% of the pregnant women were tested positive for CHIKV specific antibodies (13.8% for both IgM and IgG, 4.3% for IgM, 0.1% for IgG only) which provided a congruent estimate with the 16.5% attack rate calculated from the surveillance-system.
In s2, the seroprevalence in community was estimated to 38.2% (95% CI, 35.9 to 40.6%). Extrapolations of seroprevalence rates led to estimate, at 143,000 and at 300,000 (95% CI, 283,000 to 320,000), the number of people infected in s1 and in s2, respectively.
In comparison, the surveillance-system estimated at 130,000 and 266,000 the number of people infected for the same periods.
Conclusions: A rapid serosurvey in pregnant women can be helpful to assess the attack rate when large seroprevalence studies cannot be done. On the other hand, a population-based serosurvey is useful to refine the estimate when clinical diagnosis underestimates it.
Our findings give valuable insights to assess the herd immunity along the course of epidemics.
Author: Patrick Gerardin, Vanina Guernier, Joelle Perrau, Adrian Fianu, Karin Le Roux, Philippe Grivard, Alain Michault, Xavier de Lamballerie, Antoine Flahault and Francois Favier
Credits/Source: BMC Infectious Diseases 2008, 8:99
Published on: 2008-07-28
Copyright by the authors listed above - made available via BioMedCentral (Open Access). Please
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