Figure 2. In three areas of Brazzaville city: distribution of CHIKV seropositive (IgG) blood donors before the outbreak (A); distribution of suspected and confirmed (CHIKV+ve patients) cases during the outbreak (B); summary of seroprevalence and incidence data (C); distribution of CHIKV+ve cases (D).

Of note, suspected cases included patient who reported evocative symptoms in the previous eight days. Since the duration of viraemia is usually shorter, this may lead to underestimate the ratio CHIKV+ve/CHIK suspected cases, but does not hamper the comparison of values amongst the three areas considered.