International Journal of Epidemiology 2000;29:933-940
© International Epidemiological Association 2000
Effectiveness of incidence thresholds for detection and control of meningococcal meningitis epidemics in northern Togo
a Epicentre, 8 rue Saint-Sabin, 75011 Paris, France.
b Direction Générale de la Santé, Ministère de la Santé, BP 336, Lomé, Togo.
Background Early outbreak detection is necessary for control of meningococcal meningitis epidemics. A weekly incidence of 15 cases per 100 000 inhabitants averaged over 2 consecutive weeks is recommended by the World Health Organization (WHO) for detection of meningitis epidemics in Africa. This and other thresholds are tested for ability to predict outbreaks and timeliness for control measures.
Methods Meningitis cases recorded for 19901997 in health centres of northern Togo were reviewed. Weekly and annual incidences were determined for each district. Ability of different weekly incidence thresholds to detect outbreaks was assessed according to sensitivity, specificity, and positive and negative predictive values. The number of cases potentially prevented by reactive vaccination in 1997 was calculated for each threshold.
Results Outbreaks occurred in 19951996 and in 19961997. The WHO-recommended threshold had good specificity but low sensitivity. Thresholds of 10 and 7 cases per 100 000 inhabitants in one week had sensitivity and specificity of 100% and increased the time available for intervention by more than one or two weeks, respectively. A maximum of 65% of cases could have been prevented during the 1997 epidemic, with up to 8% fewer cases prevented for each week of delay in achieving vaccine coverage.
Conclusions In northern Togo, thresholds of 7 or 10 cases per 100 000 inhabitants per week were excellent predictors of meningitis epidemics and allowed more time for a reactive vaccination strategy than current recommendations.
Keywords Meningitis, meningococcal, epidemic, threshold, vaccination, Africa, sensitivity, specificity
Accepted 3 March 2000
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