A case of hepatitis A infection presumed to be related to asari clams and investigation on spread of viral contamination from asari clams.

In a case of hepatitis A infection that occurred in 2017 in Nagano Prefecture, hepatitis A virus (HAV) was detected in asari clams (reference food) and the patients' fecal samples. Initially, the asari clams were suspected to be the infection source. However, as a patient who had not consumed a asari clam dish also developed the disease, the exact infection route remained unknown. Suspecting a secondary infection originating from the asari clams, we investigated the presence of HAV genomes in water used for washing and soaking the frozen asari clams and detected HAV in the "Soaking Water." These results suggest that Soaking Water may be a risk factor for secondary contamination from the leakage of HAV accumulated in the asari clam midgut gland. Investigating the asari clam sand removal process, the water spewed from the asari clams scattered across a wide area in a concentric fashion, raising concern that this process itself may aggravate contamination. In addition to HAV, diarrhea viruses such as norovirus have often been detected from bivalves, including asari clams. Thus, handling these foodstuffs requires adequate care.