Intestinal parasite carriage in workers exposed to sewage

The presence of protozoan cysts and helminth eggs in sewage and the very low minimal infective doses of parasites suggest an occupational risk for workers exposed to sewage. The objective of this study was to assess this risk in a group of raw sewage-exposed workers. The relationship between sewage exposure and intestinal parasite carriage was estimated by a multiple cross-sectional survey comparing yearly prevalence rates in 126 employees working in sewers in Paris, France, with the prevalence rate in 363 food-handlers employed between 1988 and 1993. The incidence of intestinal parasitic infestation was estimated among sewage-exposed workers. Four parasite species were identified among sewage-exposed workers: whipworm, Giardia lamblia, Entamoeba coli and Endolimax nanus. The prevalence mean of intestinal parasite carriage was 11.8% (57/480), related to the presence of protozoa in 91% of samples. G. lamblia was present in 3.5% (17/480) of samples. The incidence of positive parasitological stool examination was 5.9/100 person-years. The incidence of G. lamblia in stool examinations was 1.7/100 person-years. Age-adjusted odds ratios were significantly higher in exposed workers in 1988 (OR: 6.5; 95% CI: 2.0-14.5), 1990 (OR: 4.4; 95% CI: 1.2-10.1) and 1991 (OR: 3.4; 95% CI: 1.0-8.2), but not during the other three years. The results of this study emphasize an occupational risk of intestinal protozoan infestation in workers exposed to sewage. The decrease of adjusted OR with time reflects the efficacy of compliance with rules of hygiene.