Limitations of Early Warning Systems in Elderly Populations: A Silent Outbreak, Izmir, 2025

Abstract Background Early warning systems are used to detect outbreaks, but they may not be sufficient to measure vulnerable groups. In this study, we aimed to evaluate cases of gastroenteritis in elderly people in a nursing home who were not detected by the early warning systems. Methods The outbreak occurred between 14-25 March 2025 in Izmir Metropolitan Municipality Zubeyde Hanim Nursing Home. A questionnaire consisting of 15 questions was used to collect data in this retrospective cohort study. Probable cases were the residents at Izmir Metropolitan Municipality Social Life Campus Zubeyde Hanim Nursing Home and all personnel working between 13-25 March 2025 who have at least two of the complaints of fever, nausea, vomiting, diarrhea and abdominal pain between 13-25 March 2025. Microbiological analysis was conducted for the suspected foods including lunch and dinner on 13 March 2025, drinking water of the nursing home and patients. Results 67 of 407 residents were defined as probable cases (attack rate=16.5%). 10 of the cases were hospitalized and two of the cases died (case fatality rate=3.0%). Mean age of cases and non-cases were respectively 81.6±6.6 years and 77.5±7.9 years (p < 0.001). Attack rates were 30.6% in women and 6.3% in males (p < 0.001). Relative risks (95%CI) for foods and water were unreliable due to limitations for history taking of elderly people. One personnel affected from gastroenteritis had positive result for norovirus in fecal examination. Conclusions In this example, the Municipality had followed the guidelines of the communicable diseases, and the silent outbreak was ended in two weeks. Although we could not find the definite evidence about norovirus outbreak in residents, based on epidemiological data it was estimated that this outbreak was caused by person-to-person transmission of a visitor. Key messages • Traditional early warning systems may not be sensitive for vulnerable populations to detect outbreaks. • Institutions with populous vulnerable populations should have epidemiological detection system for possible outbreaks.