Soil-Transmitted Helminthiasis (STH) is caused by infection with nematodes Ascaris lumbricoides (roundworm), Ancylostoma duodenale and Necator americanus (hookworm) and Trichuris trichura (whipworm)

STH's are known to be highly endemic across Tanzania with hospital records suggesting that all regions have some level of infection. This could be up to 100% for STH in certain ecological settings. The major contributory factors to such high levels of infection are limited access to safe water and lack of or poor environmental sanitation. For example, 33.6% of mothers admit to disposing of their children's stools within the immediate vicinity of their dwelling thus encouraging the transmission of STH's.

Throughout 2004, a nationwide epidemiological survey in schools of schistosomiasis and STH was conducted in order to prioritize areas for control as a prerequisite for implementation. All 24 regions across the country were found to require some level of intervention according to WHO guidelines.