LAUSR

A prospective matched case‐control study was conducted to evaluate associations between dietary histories, including consumption of bivalves, diarrhea, and norovirus positive diarrhea in adult ambulatory patients at an outpatient clinic of a hospital in Tokyo, Japan. Ambulatory cases with diarrhea were matched with nondiarrheal control patients, who visited the same clinic. A standardized questionnaire was used to obtain patients’ information, including histories of food consumption and clinical information. Norovirus infection was confirmed using real‐time reverse transcription polymerase chain reaction. A total of 207 patients, including 69 diarrheal cases and 138 nondiarrheal cases were included in the analysis. Among them, 60 (29.0%) participants reported consuming bivalves. Norovirus was detected in 35% (24/69) of diarrheal cases. Of those, 10 (41.7%) reported consumption of bivalves and of those, 6 (60.0%) consumed raw bivalves. The proportion of those who consumed raw bivalves was significantly higher in norovirus‐positive diarrheal cases than in norovirus‐negative diarrheal cases (25.0% vs 6.7%; odds ratio [OR], 4.67; 95% confidence interval [CI], 1.1‐20.7) and matched nondiarrheal controls (25.0% vs 6.3%, OR: 5.00; 95% CI, 1.1‐22.2). The attributable fraction of consuming raw bivalves for norovirus‐associated diarrhea to matched nondiarrheal controls was 20.0%. Consuming raw bivalves was substantially attributed to norovirus‐associated diarrhea in adult ambulatory patients and preventive measures for reducing the risk associated with consumption of raw bivalves could decrease the incidence of norovirus‐associated diarrhea.