Ice-associated norovirus outbreak predominantly caused by GII.17 in Taiwan, 2015

Abstract

Background: On 5 March 2015, Taiwan Centers for Disease Control was notified of more than 200 students with gastroenteritis at a senior high school during excursion to Kenting. We conducted an outbreak investigation to identify the causative agent and possible vehicle of the pathogen.

Methods: We conducted a retrospective cohort study by using a structured questionnaire to interview all students for consumed food items during their stay at the resort. Students were defined as a gastroenteritis case while having vomiting or diarrhea after the breakfast on 4 March. We inspected the environment to identify possible contamination route. We collected stool or vomitus samples from ill students, food handlers and environmental specimens for bacterial culture for common enteropathogens, reverse transcription polymerase chain reaction (RT-PCR) for norovirus and enzyme-linked immunosorbent assay (ELISA) for rotavirus. Norovirus PCR-positive products were then sequenced and genotyped.

Results: Of 267 students enrolled, 144 (54%) met our case definition. Regression analysis revealed elevated risk associated with iced tea, which was made from tea powder mixed with hot water and self-made ice (risk ratio 1.54, 95% confidence interval 1.22-1.98). Ice used for beverages, water before and after water filter of the ice machine and 16 stool and vomitus samples from ill students were tested positive for norovirus; Multiple genotypes were identified including GI.2, GI.4 and GII.17. GII.17 was the predominant genotype and phylogenetic analyses showed that noroviruses identified in ice, water and human samples were clustered into the same genotypes. Environmental investigation revealed the ice was made by inadequate-filtered and un-boiled water.

Conclusions: We identified the ice made by norovirus-contaminated un-boiled water caused the outbreak and the predominant genotype was GII.17. Adequately filtered or boiled water should be strongly recommended for making ice to avoid possible contamination.

Keywords: GII.17; Gastroenteritis; Ice; Norovirus; Outbreak; Water borne.

Fig. 1

The epidemic curve of gastroenteritis cases in students. N = 127, because four students reported having illness on 5 March but did not mention the exact hour

Fig. 2

Phylogenic tree of partial noroviruses VP1 gene in human and water specimens. (a) genogroup I (b) genogroup II of partial norovirus capsid VP1 gene sequences (GI according to reference sequence KF306212 at 5339–5668; GII according to reference sequence KU561249 at 5051–5373) were aligned and phylogenetic trees were generated using the neighbor-joining method by MEGA 4.0 software. Bootstrap values of 1000 replications are shown on the branches. Green color and purple color indicate norovirus from the water and human specimens, respectively. Reference sequences from GenBank are named by genotype, accession number, country and year of detection. The GenBank accession numbers of the GII.17 sequences from patient 1~4, 6~13, 16~19 are MF996723-MF996738 and the GI strains sequences from patient 5, 10, 11, 14, 15 are MF996717- MF996722