Diarrheal disease surveillance in Gizan (population 590,088) in late 1992 revealed an increase in diarrhea following unusually heavy rains. The causative organism and mode of transmission were not known.
Methodology
We reviewed diarrhea surveillance data for four years. We selected the Samtah sector because it had the highest incidence rate. Within Samtah, two villages were selected -- one with a high incidence of diarrhea (Gawwa) and one with a low incidence (Jadea). We surveyed 25% of children under 5 years old. We questioned families about possible exposures and took stool samples for bacteriology and parasitology.
Results
Surveillance revealed a large diarrhea outbreak in Samtah during one month. Our survey conducted four months later showed only "Giardia lamblia", with a 50% prevalence rate in Gawwa and 9% in Jadea. "Giardia" infection was not associated with diarrhea. The prevalence of giardiasis associated with using open wells was 62% in Jadea (relative risk=16.9; 95% confidence interval=4.8-59.2). All houses in Gawwa used open wells. No other risk factors were associated with diarrhea or giardiasis.
Conclusion
Since this outbreak occurred four months before our investigation, we cannot prove that "Giardia" caused the outbreak. The high "Giardia" prevalence in the village using exclusively open wells and the association with open wells in the other village suggest that waterborne giardiasis was present.