Investigation of an acute gastroenteritis epidemic caused by norovirus infection in a middle school in Songtao, Tongren, Guizhou, 2023

Objective To understand the clinical and epidemiological characteristics of an acute gastroenteritis epidemic in a middle school in Songtao county, Tongren of Guizhou province in February 2023, analyze possible risk factors and provide reference for epidemic prevention and control.

Methods Field epidemiological methods were used in the investigation. The clinical symptoms and distributions of the cases were analyzed by descriptive epidemiological methods. The risk factors of the epidemic were identified by case control study. Anal swabs, vomit, environmental smears and residual food samples were collected from both cases and controls. Real time fluorescence quantitative reverse transcription polymerase chain reaction (RT-PCR) was used to detect norovirus and common pathogenic bacteria.

Results In this epidemic, 12 students and 2 teachers were infected, and the attack rates were 6.70% (12/179) and 5.13% (2/39), respectively. Four classes were involved, the cases were mainly distributed in Class 9 (1) with the attack rate of 20.83% (5/24). There was no significant difference in attack rate between boy students and girl students (χ²=3.470, P=0.062). The main symptoms were diarrhea (100.00%), abdominal pain (78.57%), nausea (71.43%) and vomiting (42.86%). The onset time of the first and last cases was at 12:00 on February 24 and at 18:00 on March 2, respectively. The incidence peak was during 26-28 February, and the epidemic curve showed a value-added person-person pattern. Two strain of norovirus GⅠ and 1 strain of norovirus GⅡ were detected in the anal swab samples of one student and two teachers. Case-control study showed that 71.43% (10/14) of cases had close exposures to vomit or feces from the patients odds ratio (OR) = 32.500, 95% confidence interval (95%CI): 3.127–337.813, P<0.001 and contacts with the patients (OR=6.250, 95%CI: 1.213–32.214, P<0.001), which might be the risk factors of this epidemic, and other factors were not statistically associated with the epidemic.

Conclusion This epidemic was caused by the infection of norovirus GⅠ and GⅡ, Close exposure to vomit of the patients and contact with the patients were the risk factors. Improper disposal of vomit was the possible cause of the spread of this epidemic. Therefore, it is necessary to improve the disposal of vomit and strengthen health education about hand hygiene for the prevention and control of such epidemic.