Characteristics of cases of hepatitis E in 2019 in Gunma prefecture: a small epidemic caused by the same subgenotype 3a strain

In 2019, the number of reported cases of hepatitis E in Gunma prefecture was 1.44 per 100,000 people, which was the highest in all of Japan. We examined the clinical characteristics of 20 cases of hepatitis E reported in 2019 and analyzed the hepatitis E virus (HEV) genomes of seven sporadic cases. All HEV strains isolated from these cases belonged to subgenotype 3a and were 99.7% to 100% identical to each other within the 412-nucleotide ORF2 sequences. Of these seven cases, six had eaten raw or undercooked pig liver/intestine within the past three months, suggesting that they had been infected with a swine-derived HEV strain. When a small epidemic is suspected, HEV genome analysis should be performed to identify the cause of infection, even in sporadic cases.