The health department held a news conference discussing the three confirmed cases of E. coli in Hyrum’s High Valley subdivision in Utah. But officials declined to speculate on the source of the intestinal illness, according to the Deseret Morning News.

Health department teams from the Bear River Health Department have made direct contact with many of the people in the subdivision — a small area that includes about 40 houses on two streets and a cul-de-sac — in an attempt to discover how each person became infected.

Some subdivision residents worry the contamination stems from work being done on city water lines.