Improved measles surveillance in Cameroon reveals two major dynamic patterns of incidence

Objective: To characterize the province-specific incidence patterns of measles in Cameroon and determine if an increase in measles incidence during the period January 2000-June 2001 is consistent with coincident epidemics in several regions with different inter-epidemic periods. Method: Periodic behavior of the monthly measles incidence time-series from each province of Cameroon was analyzed using time-series analysis and cluster techniques. Cumulative incidence in each province of Cameroon over a five-year period was associated with birth rates, and vaccination coverage. Results: Distinct patterns of measles incidence were found in two different areas of Cameroon. The three northern-most provinces experience major epidemics every year. Seven southern provinces show evidence of experiencing major epidemics every third year. In January 2000, Cameroon experienced coincident peaks in these two cycles and thus an increase in measles incidence countrywide over the previous year. Higher cumulative province-specific incidence rates were associated with higher birth rates and lower routine vaccination coverage rates. Conclusion: Within one country, two dramatically different dynamic patterns of measles incidence were observed. Long-term surveillance data is crucial to the evaluation of measles immunization campaigns. The availability of a five-year record of measles incidence in Cameroon reveals an interesting dynamic pattern of measles incidence that accounts for the increase in countrywide incidence in 2000-2001.