ABSTRACT
<p><b>OBJECTIVE</b>To investigate the cause of an outbreak characterized by diarrhea and vomit in a middle school in Huzhou City.</p><p><b>METHODS</b>Comprehensive analysis was conducted based on field epidemiological study, clinical characteristics of the cases and laboratory test.</p><p><b>RESULTS</b>578 cases of acute gastroenteritis were found. The attack rate was 23.58%. The most frequently observed clinical symptoms were diarrhea, vomiting, abdominal pain and nausea. Some few had fever. Most cases had slight clinical symptom with a course from 1 to 3 days. The cases were distributed in every class, showing no phenomenon of clustering. Norovirus were detected in 11 out of 15 stool samples by using RT-PCR. 6 were genogroup II norovirus. 3 were genogroup I norovirus. enogroup I and II norovirus were detected at the same time in 2 stool samples (the same student with 2 tests). Case-control study showed that drinking unheated bottled water was risk factor (OR = 2.46, 95% CI = 1.19-5.23), and had a dose response relation with the disease (chi = 24.8 P < 0.01). The epidemic was controlled soon through isolating patients during treatment, providing boiled water, disinfecting and health education.</p><p><b>CONCLUSION</b>This was an infectious diarrhea outbreak caused by norovirus. The suspected transmission ways were drinking unheated bottled water and contact daily.</p>