In northern Kazakhstan, a rural village experienced a surge in acute gastroenteritis cases in mid-2021. Between May 14 and June 15, residents presenting with diarrhea, fever above 37.5 °C, vomiting, or generalized weakness were considered cases. For each case, two age-matched controls (±2 years) from the same village were selected. Information was gathered through structured interviews, and medical records were reviewed for clinical details. Case locations were plotted, and conditional multivariable logistic regression was used to identify factors associated with illness. A total of 154 residents were affected, yielding an attack rate of roughly 26 per 1,000. The most frequently reported symptoms were fever, diarrhea, weakness, vomiting, and reduced appetite. Among those interviewed, 74% of cases reported drinking unboiled tap water, compared with 18% of controls. Statistical analysis identified consumption of unboiled tap water as the primary risk factor (adjusted odds ratio: 18; 95% CI: 9–35), while drinking water from dispensers or carbonated beverages appeared to reduce risk. Cases were concentrated in a single water supply network, involving 79 households. The outbreak investigation revealed that water quality monitoring had been neglected since 2018, violating national regulations. No deaths occurred, and no additional cases were reported following intervention. Untreated tap water was determined to be the most likely source. The affected water supply had been disinfected twice two days prior to the investigation. Authorities were advised to implement regular water quality assessments and timely public alerts to prevent similar outbreaks in the future.
