| Summary: | INTRODUCTION: In January 2010, the Virginia Department of Health received reports of 2 hepatitis B virus (HBV) infections (1 acute, 1 chronic) among residents of a single assisted living facility (ALF). Both infected residents had diabetes and received assisted monitoring of blood glucose (AMBG) at the facility. An investigation was initiated in response. OBJECTIVE: To determine the extent and mechanism of HBV transmission among ALF residents. DESIGN: Retrospective cohort study. SETTING: An ALF that primarily housed residents with neuropsychiatric disorders in 2 adjacent buildings in Virginia. PARTICIPANTS: Residents of the facility as of March 2010. MEASUREMENTS: HBV serologic testing, relevant medical history, and HBV genome sequences. Risk ratios (RR) and 95% confidence intervals (CIs) were used to identify risk factors for HBV infection. RESULTS: HBV serologic status was determined for 126 (91%) of 139 residents. Among 88 susceptible residents, 14 became acutely infected (attack rate, 16%), and 74 remained uninfected. Acute HBV infection developed among 12 (92%) of 13 residents who received AMBG, compared with 2 (3%) of 75 residents who did not (RR = 35; 95% CI, 8.7, 137). Identified infection control breaches during AMBG included shared use of fingerstick devices for multiple residents. HBV genome sequencing demonstrated 2 building-specific phylogenetic infection clusters, each having 99.8-100% sequence identity. LIMITATIONS: Transfer of residents out of the facility prior to our investigation might have contributed to an underestimate of cases. Resident interviews provided insufficient information to fully assess behavioral risk factors for HBV infection. CONCLUSIONS: Failure to adhere to safe practices during AMBG resulted in a large HBV outbreak. Protection of a growing and vulnerable ALF population requires improved training of staff and routine facility licensing inspections that scrutinize infection control practices.
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