Association of respiratory tract infection symptoms and air humidity with meningococcal carriage in Burkina Faso.

Objectives: To evaluate risk factors for meningococcal carriage and carriage acquisition in the African meningitis belt, comparing epidemic serogroup A (NmA) to non-epidemic serogroups.

Methods: During the non-epidemic meningitis season of 2003, pharyngeal swabs were taken at five monthly visits in a representative population sample (N = 488) of Bobo-Dioulasso, Burkina Faso (age 4-29 years) and analysed by culture. Standardized questionnaires were administered. In 2006, a similar study was performed in 624 individuals (age 1-39 years) during an NmA meningitis epidemic. We evaluated serogroup-specific risk factors for carriage, carriage acquisition and clearance using multivariate logistic and Poisson regression, and a Cox proportional hazard model.

Results: The prevalence of NmA carriage (current or recent pharyngitis or rhinitis) was 16% (31%) vs. 0% (9%) in the epidemic vs. the hyperendemic setting. During the epidemic situation, NmA carriage was significantly associated with recent sore throat (adjusted odds ratio (OR), 3.41) and current rhinitis (OR 2.65). During the non-epidemic meningitis season in 2003, air humidity (20-39% and >or=40%, compared to <20%) during the month before swabbing was significantly and positively associated with carriage acquisition of non-groupable meningococci (OR 2.18 and 1.55) and inversely with carriage clearance (hazard ratio 0.61 and 0.27, respectively).

Conclusion: Respiratory tract infections may increase meningococcal carriage, and thus contribute to epidemic risk, in addition to seasonality in the meningitis belt. Humid climate may favour carriage of unencapsulated meningococci. These findings may help identifying interventions against epidemic and hyperendemic meningococcal meningitis due to non-vaccine serogroups.