The Gambia and Bangladesh: the seasons and diarrhoea.

Climactic factors in the Gambia and Bangladesh have an important impact on the incidence of diarrheal disease. Both countries share some common characteristics in climate including a cool dry winter of 3 months followed by a hot dry spring and hot wet summers of 5-7 months in length. The main difference is in the amount of rainfall. The Gambia may have 20-30 inches of rain each year; Bangladesh usually has up to 4-5 times this amount. In the Gambia drought is a recurring problem; floods is the problem in Bangladesh. A study in the Gambia found a close link between the time of the annual peak in diarrhea in young children and the summer rains. A 2nd peak of diarrhea in the winter also was significant and was shown to coincide with a short period of intense transmission of rotavirus. Of the enteric infections of childhood the enterotoxigenic "Escherichia coli" (ETEC) that is those producing heat-stable toxin (ST) were found to be the most important etiological agents of diarrhea in both countries with a peak during the rains. In rural Gambia water is obtained almost exclusively from surface wells 15-20 meters deep. It was found that although this water was fecally contaminated throughout the year levels of contamination increased by up to 100 times with 1-2 days of the start of the rains because excreta is washed into the wells. It also was clear that contaminated water and domestic environment contribute to contamination of childrens food. The high level of contamination of food during the summer coincided with the time of high diarrhea prevalence. In Bangladesh it was shown that the incidence of ETEC diarrhea in infants was positively correlated with the frequency of consumption of weaning foods contaminated with fecal coliforms. The seasonal peak of ETEC diarrhea coincided with the time when food was most contaminated due to higher bacterial growth caused by high temperatures. Cholera is endemic in many areas of Bangladesh but not in the Gambia. Though similar some other diarrheal diseases in showing a rainy season peak the timing of peaks of cholera incidence can and has changed from year to year in Bangladesh. The reason for this and the variable occurence of a less marked pre-rains peak of cholera is unknown. During the main farming season mothers have less time for breastfeeding. Smaller amounts of breast milk were consumed by breastfeeding infants at this time of year coinciding with poorer maternal nutritional status. This also was the season of poorest nutritional status in children leading to increased duration and perhaps severity of diarrhea. Personal hygiene attitudes toward breastfeeding and weaning practices are important non-seasonal factors in diarrheal diseases. To be more effective health education messages could be varied according to the season for different problems occur at various times of the year.