Résumé
The investigation of this outbreak took place in Niakhar (IRD project study area), a rural area located 150 km East of Dakar. Covering 30 villages, with a population of about 30,000 inhabitants, the area has been under demographic and epidemiological surveillance. In 1999, the surveillance allowed 973 cases of shigellosis to be recorded out of 1,751 cases of dysenteric diarrhoeas. The outbreak reached a peak during the raining season (73% of the cases in September and October). All the villages and all age groups were concerned. The attack rate in the population was 3%. During the same period, 22 deaths were attributed to shigellosis, leading to a lethality of 2.3%. Children under five were the most affected. The bacteriological examination isolated S. flexneri in 72% of 12 stools samples and S. dysenteriae A1 (SD1) in 14%. All serotypes were resistant to ampicillin and susceptible to quinolones. Susceptibility to cotrimoxazole was unconstant. Apart from the usual factors involved in the spread of diarrhoeas, the main reason evoked to explain the duration of the epidemic has been the lack of adequate emergency antibiotherapy treatment. Quinolones, recommended by the health authorities, could not be provided by health services. The identification of the SD1 serotype confirmed its involvement in the outbreak of shigellosis. The exact role of S. flexneri in shigellosis epidemics should be further studied.