Epidemiological Evidence for Helminth and Cholera Transmission by Vegetables Irrigated with Wastewater: Jerusalem – A Case Study

Abstract

This paper reviews and reanalyzes epidemiological data on the transmission of the helminthic diseases ascariasis and trichuriasis as well as cholera by vegetables and salad crops irrigated with untreated wastewater in Jerusalem between 1935 and 1982, based on a series of published papers and unpublished reports not generally available to professionals in the field of water pollution control. The findings provide strong evidence that both Ascaris and Trichuria infections were actively and massively transmitted to the general public who consumed vegetables irrigated with raw wastewater. The levels of infection dropped dramatically when the supply of contaminated vegetables was cut off but increased again rapidly on reintroduction of the wastewater-irrigated crops. The infection level subsided again when the practice was finally stopped in 1970. The epidemiological evidence from the 1970 cholera outbreak in Jerusalem indicates that wastewater-irrigated vegetables were the primary route of secondary infection once a few subclinical or clinical cases of cholera entered the city from areas outside the country where a cholera epidemic was underway. The evidence also indicates that farmers in an area where cholera is not endemic are particularly at risk when practicing irrigation with raw wastewater from a city underdoing a cholera outbreak. The need to treat wastewater to remove these pathogens prior to the irrigation of such vegetable crops is stressed.