More than 600 people fell sick in Greece in early 2019 with contaminated tap water the most likely source, according to a recent research report.

In total, 638 gastroenteritis cases were recorded with symptom onset from late January to early February 2019. However, scientists estimated the actual burden of disease was much higher, according to their manuscript accepted by the journal Epidemiology and Infection.

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.

Lab confirmation not possible
Researchers conducted a case control study with participants older than 16, residents of the town in Northern Greece, who visited the health care center in late January. This 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.

The scientists also did a retrospective cohort study with 236 students at four elementary schools in the town. Seventy-one percent of the cases were absent from school for at least one day. Tap water consumption in two days prior to onset of symptoms was associated with the gastroenteritis cases.

In Greece, 32 waterborne outbreaks were recorded between 2004 and 2018 and seven of them affected more than 200 people.

The waterborne origin of the outbreaks was not confirmed. More than one pathogen was detected from stool samples of six of 11 cases tested. Four were positive for two pathogens and two were positive for three pathogens each. Campylobacter was most common as it was found in eight clinical samples and norovirus was found in five. Campylobacter was detected with various pathogens, mostly diarrheagenic E. coli. Water samples were not tested for parasites because there isn’t a dedicated laboratory.

How was water contaminated?
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.

There were no livestock holdings close to the springs or tanks’ area and the wastewater pipeline was not close to the drinking water pipe. There was no extreme weather in the area in January 2019.

“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 from a single person. The outbreak investigation did not lead to a definitive conclusion on how water might have been contaminated, 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.

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