Estimating Chikungunya prevalence in La Réunion Island outbreak by serosurveys: two methods for two critical times of the epidemic

• Published in: BMC infectious diseases 2008-07, Vol.8 (1), p.99-99, Article 99
• Main Authors: Gérardin, Patrick, Guernier, Vanina, Perrau, Joëlle, Fianu, Adrian, Le Roux, Karin, Grivard, Philippe, Michault, Alain, de Lamballerie, Xavier, Flahault, Antoine, Favier, François
• Format: Article
• Language: English
• Subjects: Alphavirus Infections - epidemiology; Alphavirus Infections - immunology; Antibodies, Viral - blood; Antibodies, Viral - immunology; Causes of; Chikungunya fever; Chikungunya virus - immunology; Chikungunya virus - isolation & purification; Control; Cross-Sectional Studies; Disease Outbreaks; Distribution; Enzyme-Linked Immunosorbent Assay; Epidemiology; Female; Humans; Immunoglobulin G - blood; Immunoglobulin M - blood; Pregnancy; Pregnancy Complications, Infectious - epidemiology; Prevalence; Reunion - epidemiology; Sentinel Surveillance; Seroepidemiologic Studies; Surveys
• ISSN: 1471-2334; 1471-2334
• DOI: 10.1186/1471-2334-8-99

Chikungunya virus (CHIKV) caused a major two-wave seventeen-month-long outbreak in La Réunion 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. 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. 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. 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.