Eligible studies were case-control or cohort studies, non-randomised trials, or cross-sectional studies that evaluated the effects of any piped sewerage intervention compared with the pre-sewerage sanitation situation on diarrhoea or specified enteric infections (including helminth infection) in children or adults in any region of the world.
Most studies included in the review compared sewerage with another type of sanitation, such as flush toilets discharging to septic tanks or open drains. The age of the participants varied, but most of the studies were conducted in children up to 14 years of age. The primary outcomes reported were diarrhoea incidence and Giardia species infection incidence (in stool samples). One study evaluated Cryptosporidium infection using antibody incidence in the blood serum (seroprevalence). Outcomes were assessed/reported in the past day, or in the past two or four weeks. The comparators were poorly described in the included studies; they were mostly described as 'no sewerage'.
Most included studies were conducted in Brazil; the other studies were conducted in middle income countries such as Mexico, Nicaragua, Honduras, Peru, the USA, Iran, Syria, Saudi Arabia, and Australia.
Two reviewers independently selected the studies for inclusion; no disagreements arose.