A waterborne outbreak involving hepatitis A virus genotype IA at a residential facility in the Republic of Korea in 2015

•In 2015, a waterborne outbreak of hepatitis A occurred at a residential facility for the disabled.•Of 82 people, 12 were diagnosed with hepatitis A, and one patient died.•Identical VP3-VP1 regions from HAV genotype IA were detected in both clinical and groundwater samples. Hepatitis A virus (HAV), a major cause of acute hepatitis, has had the highest occurrence among group 1 nationally notifiable infectious diseases in Korea since 2010.Recently,the annual increase in the HAV infection rate among young adults has become a public health concern. The aim of this study was to describe an outbreak of acute hepatitis in a residential facility in April 2015 and to identify potential sources of this outbreak. Sera from all exposed residents were tested for anti-HAV IgM or IgG antibodies by ELISA. Clinical (sera and stool) and environmental samples were screened for the presence of HAV RNA using one-step RT-PCR and nested PCR. The VP3-VP1 regions of HAV were analyzed using the BLAST database and MEGA7 software. Of the 82 persons in the facility, 12 (14.6%, including 10 residents and 2 health care workers) were diagnosed with hepatitis A. Clinical symptoms were evident in 9 individuals, one of whom died, and the remaining four patients were asymptomatic. Traceback investigation revealed that HAV-RNA (genotype IA) was detected in the patients’ stools and the groundwater used in the facility. We described an HAV outbreak in a facility for the disabled due to using a water supply that was mixed with contaminated groundwater. Therefore, HAV vaccination and periodic water inspections in group facilities should be emphasized to prevent HAV infection.