**Background:** Infectious diarrhea remains a leading cause of morbidity and mortality in children worldwide, responsible for approximately 500,000 deaths annually in children. In China, it accounts for nearly 20% of notifiable infectious diseases. Preschool children aged 3–6 years are particularly vulnerable due to unstable hygiene habits and relatively low immunity, and infections can lead to cluster outbreaks in childcare facilities. While prior research has focused on children under 5 years, there is a knowledge gap regarding pathogen characteristics, seasonal patterns, and influencing factors specifically in preschool children attending kindergarten.
**Methods:** This matched case-control study was conducted from January 2017 to December 2020 at a hospital in Ningbo, China. The sample size was calculated based on prior similar studies (target: 258 per group, 516 total, assuming 15% attrition). Initially, 352 infection cases and 370 controls were enrolled; after applying inclusion/exclusion criteria and 1:1 matching by gender, age (±6 months), and parental education level, 260 children per group were included. Inclusion criteria: age 36–71 months, kindergarten attendance ≥3 months, abnormal stool character (bloody, mucous, or watery) with fever/vomiting, and laboratory-confirmed pathogens. Exclusion criteria: noninfectious diarrhea, irritable bowel syndrome, cognitive disorders, malignancies, immunosuppressant/antibiotic use within 3 months, or missing data. Data were collected from medical records and a structured questionnaire completed by parents via face-to-face or telephone interviews, adapted from prior studies under epidemiologist guidance. Stool samples underwent microscopic examination, bacterial culture/serology, and viral identification by real-time PCR and ELISA. Univariate analysis (χ² test, rank sum test) identified candidate variables (P < .05), which were entered into multivariate logistic regression.
**Key Results:** The top 5 pathogens among 260 infected children were Salmonella (15.77%, n=41), rotavirus (13.85%, n=36), Shigella (11.54%, n=30), Vibrio (10.38%, n=27), and norovirus (8.85%, n=23). Peak months were January (13.85%), December (12.69%), August (12.31%), February (11.92%), and July (8.46%), showing winter and summer predominance. Demographic variables (gender, age, BMI, residence, parental age/marital status/education/income) did not differ significantly between groups. Univariate analysis identified 10 significant factors (all P < .05): recent exposure to diarrhea, previous history of diarrhea, rotavirus vaccination, regular hand-washing, tableware disinfection, separate preparation of cooked and raw foods, regular eating leftovers, regular intake of lactobacillus products, regular eating out, and flies/cockroaches indoors. Multivariate logistic regression confirmed 7 independent factors. Risk factors: recent exposure to diarrhea (OR 3.789, 95% CI 1.852–7.750, P < .001) and flies/cockroaches indoors (OR 1.839, 95% CI 1.192–2.836, P = .006). Protective factors: rotavirus vaccination (OR 0.503, 95% CI 0.298–0.849, P = .010), regular hand-washing (OR 0.372, 95% CI 0.183–0.755, P = .006), tableware disinfection (OR 0.633, 95% CI 0.434–0.923, P = .018), separate preparation of cooked and raw foods (OR 0.524, 95% CI 0.360–0.762, P = .001), and regular intake of lactobacillus products (OR 0.451, 95% CI 0.294–0.692, P < .001). Vaccination rates were low: 29.23% in infected children vs 39.62% in controls.
**Clinical Implications:** This study provides specific evidence for targeted prevention of infectious diarrhea in preschool children attending kindergarten. The identified protective factors—rotavirus vaccination, hand hygiene, food separation practices, tableware disinfection, and lactobacillus product consumption—are actionable interventions that can be implemented at home and in childcare settings. The two risk factors (recent exposure to diarrhea and indoor flies/cockroaches) underscore the importance of environmental sanitation and isolation measures during outbreaks. The low rotavirus vaccination rate (29–40%) highlights a critical gap in prevention, as rotavirus vaccination is optional in China. Limitations include the single-center design in urban Ningbo (limiting generalizability), potential recall bias from questionnaire data, unclear pathogen origins in some cases, and the inability to extend findings to the general population or other age groups. The authors call for large-sample multicenter prospective studies to validate these findings.