Laboratory study for one gastroenteritis outbreak caused by norovirus GI and Bacillus cereus

Objective To understand the etiological characteristics of an acute gastroenteritis outbreak. Methods The common enteric pathogen screening was performed for the samples from the patients (stool and vomitus) and the suspected contaminated food samples by using real time PCR. Bacteria culture was carried out according to the real time PCR results. The ces gene was tested for both the collected samples and the bacteria isolates. The Bacillus cereus isolates were sub-typed with PFGE. Results By using real time PCR, Norovirus GⅠwas detected in 25 of the 35 patients (71.43%, 25/35) and 6 B. cereus strains were detected in 5 of the 35 patients (14.29%, 5/35), including 5 strains from stool samples and 1 strain from vomitus samole. One stool sample from a cooker was positive for B. cereus by both PCR and culture method. In 7 suspected food samples, 4 were positive for B. cereus and 5 were positive for ces gene by real time PCR. The plate count culture for suspected food indicated that 1 sample had over 160 000 cfu/g bacteria. Nineteen B. cereus isolates had 14 PFGE patterns and in 5 isolates from the patients, 2 shared the same pattern with the isolate from the cooker. The isolates from the same food samples had different patterns. The 19 strains of B. cereus isolates were negative for ces gene. Conclusion Norovirus GⅠ and Bacillus cereus might be the major pathogens for this outbreak. The multi-pathogen screening with real time PCR is useful for rapid laboratory response for food-borne outbreaks.