The impact of an urban sewerage system on childhood diarrhoea in Tehran, Iran: a concurrent control field trial

SummaryThe stepwise implementation of the Tehran Sewerage Project provided a convenient setting for which health impacts of an urban sewerage system could be examined with appropriate controls. In 2001, Tehran municipal districts 17 and 18 had no sewerage system connections, but areas within these districts had been planned to be connected by 2006. These areas were chosen as an intervention group. Neighbouring areas, with a similar socio-economic status, that had not been planned to connect to the sewerage system by 2006, were chosen as controls. Homes within designated areas were randomized and surveyed twice to determine diarrhoea incidences for children aged 6–60 months, once in 2001, before connection to the sewerage system, and once again in 2006, after the intervention. By 2006, 76% of the homes in the intervention zones were connected to the sewerage system. In the first stage of the study, diarrhoea incidences for intervention and control groups were 18.6 and 16.6%, respectively. In the second stage, incidences decreased to 10.1 and 10.5%, respectively. Data collected from 4179 children demonstrated that the diarrhoea incidence had decreased by 46% in the intervention group, whereas it had decreased by 37% in the controls.