Study of a localized meningococcal meningitis epidemic in Burkina Faso: incidence, carriage, and immunity

Abstract

Background: To better understand localized meningococcal meningitis epidemics, we evaluated a serogroup A (NmA) epidemic in Burkina Faso by surveillance, carriage, and seroprevalence studies.

Methods: During March-April 2006, cerebrospinal fluid samples from patients suspected to have meningitis in 3 epidemic villages were analyzed by culture or polymerase chain reaction. We assessed meningococcal carriage and serogroup-specific serum bactericidal antibody titers with baby rabbit complement (rSBA) in a representative population sample (N = 624; age range, 1-39 years). A serogroup A/C polysaccharide vaccine campaign occurred in parallel.

Results: Cumulative incidence of Nm meningitis was 0.45% and varied among villages (0.08%-0.91%). NmA carriage prevalence was 16% without variation by vaccination status. NmA carriage and anti-NmA seroprevalence varied by village and incidence. In the 2 villages with highest incidence and seroprevalence, presence of rSBA titers ≥8 was associated with NmA carriage (odds ratio [OR], 9.33 [95% confidence interval {CI}, 1.90-45.91]) and vaccination ≤4 days earlier (OR, 0.10 [95% CI, .03-.32]). Visibly purulent or Nm meningitis was significantly associated with recent flulike symptoms and exposure to kitchen smoke (risk ratios >15).

Conclusions: A surge of NmA carriage may be involved in the development of meningococcal epidemics and rapidly increase anti-NmA seroprevalence. Flulike infection and kitchen smoke may contribute to the strength of epidemics.

Figure 1.

Geographic map of Burkina Faso, sanitary district Secteur 15, and the study villages of Lena, Kofila, and Konkourouna.

Figure 2.

Weekly incidence rates of suspected (dotted lines, empty symbols) and confirmed (solid lines, filled symbols) meningococcal meningitis cases, during a localized epidemic due to meningococcal serogroup A in western Burkina Faso, March–April 2006, by village. Black and squares, Kofila; dark gray and triangles, Lena; light gray and circles, Konkourouna. Star, timing of meningococcal group A/C polysaccharide vaccine mass campaign.

Figure 3.

Risk ratio of visibly purulent or confirmed Nm meningitis at various cutoffs (≥8, ≥512, and ≥1024) of anti-A serum bactericidal antibody titers during a localized epidemic due to meningococcal serogroup A in western Burkina Faso, 2006, among 99 unvaccinated individuals in Konkourouna. Risk ratio and 95% confidence intervals (error bars) are crude (black) and adjusted for age group, sex, and serogroup A carriage at serological assessment (gray).

Figure 4.

Prevalence of serogroup A (dark gray) and serogroup Y (light gray) meningococcal carriage by age groups in the general population during a localized epidemic due to meningococcal serogroup A in western Burkina Faso, 2006. Error bars are 95% confidence intervals.

Figure 5.

Age-specific serum bactericidal antibody titers against meningococcal serogroups A and W135, by village and vaccination status in the general population during a localized epidemic due to meningococcal serogroup A in western Burkina Faso, 2006. Black, Konkourouna and Lena, villages with high incidence and serogroup A carriage (n = 122). Gray, Kofila, village with relative low incidence and low serogroup A carriage (n = 33). Solid line and squares, vaccinated individuals; dotted line and circles, unvaccinated individuals. Error bars are 95% confidence intervals in Konkourouna and Lena. Included are only unvaccinated individuals or those with meningococcal polysaccharide A/C vaccination up to 4 days earlier. The number of eligible serum samples was insufficient for statistical analysis among unvaccinated persons of age 5–19 years in Kofila. A, Seroprevalence of anti-A titers ≥8. B, Seroprevalence of anti-A titers ≥1024. C, Geometric mean anti-A titers. D, Seroprevalence of anti-W135 titers ≥8.