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The occurrence of an outbreak of meningitis during three consecutive years in a study area under demographic and epidemiologic longitudinal surveillance allowed evaluating the impact of mass immunisation campaigns on the incidence of meningitis. During an outbreak of meningitis in the neighbouring region occurred 2 years before the first epidemic wave in the study area, 8 out of the 30 villages of the zone were immunised. The incidences of meningitis in these villages were compared with those of the villages that did not benefited from mass campaign. It appeared a very significant difference between the two groups of villages. More than a half of the cases of meningitis seemed to be avoided in the vaccinated villages compared to the others, suggesting that a previous immunisation limits the diffusion of the epidemic. After the second outbreak hit the study zone, a mass immunisation campaign concerned all the 30 villages. The incidences of meningitis were significantly different between villages according to the observed vaccine coverage. These results indicate that preventive immunisation could have a significant impact on meningitis outbreak diffusion.

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.

There have been many cholera outbreaks in Senegal since 1971. The last outbreak began in the Dakar region in August 1995. It spread to the Diourbel, Fatick, Saint-Louis and Thies regions. In January 1996, the outbreak hit the Niakhar study area in the Fatick region. A team from ORSTOM (the French Institute of Scientific Research for Development in Cooperation) has been recording demographic events in this area for almost 15 years. The geographic approach is based on the automated mapping of cholera in hamlets and villages. Such studies investigate the factors determining the spread of diseases, within the context of land use. Three sets of data were used: demographic data that had been routinely collected and were available from a database, digitized maps and epidemiological data from a surveillance system set up to monitor the outbreak. A series of incidence maps, over time and on various scales, were generated using specialized software. The maps were analyzed and the outbreak was found to be heterogeneous over time. There were two waves of the outbreak and differences according to age and gender. The degree of heterogeneity depended on the place of residence. Heterogeneity was probably determined by village size, roads and the concentration of inhabitants within hamlets, which is roughly equivalent to the number of people per bore hole. These preliminary results suggest that further research is necessary, looking at different geographical scales (e.g. households, districts and regions). Qualitative studies of water use and the organization of the water supply are also required.