Two years after 638 people in Greece were sickened by gastroenteritis, a recent research report indicated it was because of contaminated tap water and that the number of people affected was likely far higher.

The outbreak happened in late January, 2019 and lasted into early February the journal Epidemiology and Infection saying scientists have now pointed to the source with no explanation why it took so long.

Slightly more than half of those ill were female and the age of patients ranged from a few months to 93 years old. Symptoms were mainly diarrhea and vomiting. Hospitalization was required for 430 patients but no deaths were recorded.

Researchers conducted a case control study with participants older than 16, residents of the town in Northern Greece, who visited the health care center, said Food Safety News.

That involved 48 cases and 52 controls. Cases were more likely to have consumed tap water in the two days before symptom onset and to have used tap water to produce ice cubes.

There were issues with water tanks and their enclosures. Inspection of the supply system revealed technical failures; disintegration of cement, especially on tank roofs, a lack of protective surrounding enclosure in one of the tanks and of appropriate protective equipment on windows of the pumping station and tanks. Microbiological testing of water samples collected by the municipality were negative.

“As well as epidemiological evidence, a waterborne source is also supported by the outbreak’s size, the absence of a common activity or food item consumption among cases, and the fact that there was no recorded increase of gastroenteritis cases in nearby areas and villages with a different water supply system,” said researchers.

Water may have become contaminated with feces from sewage, rather than a single person as the investigation didn’t make a conclusion and whether the contamination was of human or animal origin. Low levels of residual chlorine found during the inspection could imply deficiencies in water sanitation practices.

“The outbreak led to increased awareness from local authorities on the measures needed to ensure water safety including upgrading the supply system, continuous monitoring for early detection of faults, systematic water quality control appropriate treatment processes, and protection during storage and distribution of water,” said researchers.