An outbreak of hepatitis A virus infection in a secondary school in England with no undetected asymptomatic transmission among students

Abstract

In June 2019 the Health Protection Team in Yorkshire and Humber, England, was notified of cases of hepatitis A virus (HAV) infection in staff at a secondary school. Investigation revealed that an earlier case worked as a food handler in the school kitchen. Indirect transmission through food from the canteen was considered the most likely route of transmission. Cases were described according to setting of exposure. Oral fluid was obtained from students for serological testing. Environmental investigations were undertaken at settings where food handling was considered a potential transmission risk. Thirty-three confirmed cases were linked to the outbreak. All of those tested (n = 31) shared the same sequence with a HAV IB genotype. The first three cases were a household cluster and included the index case for the school. A further 19 cases (16 students, 3 staff) were associated with the school and consistent with indirect exposure to the food handler. One late onset case could not be ruled out as a secondary case within the school and resulted in vaccination of the school population. Five cases were linked to a bakery where a case from the initial household cluster worked as a food server. No concerns about hygiene standards were noted at either the school or the bakery. Oral fluid samples taken at the time of vaccination from asymptomatic students (n = 219, 11-16 years-old) showed no evidence of recent or current infection. This outbreak included household and foodborne transmission but limited (and possibly zero) person-to-person transmission among secondary school students. Where adequate hygiene exists, secondary transmission within older students may not occur.

Keywords: Epidemiology; hepatitis A; outbreaks; public health; vaccination (immunisation).

Fig. 1.

Distribution of cases of confirmed hepatitis A virus infection by likely setting of exposure (all cases) (a) and for school-associated cases only (b) and bakery-associated cases only (c). The expected interval of symptom onset dates for school- and bakery-associated cases is based on mean (dark grey bar) and range (light grey bar) of the incubation period for HAV infection. The interval assumes exposure of individuals during the working days when a food handler was likely infectious at the setting (indicted by open circles). 1–3 = indicate first three cases, as described in the main text * Community cases include the household contacts (cases 1 & 2) of the first case among school staff (case 3). ** Household contacts are contacts of a school case. B = cases linked to Bakery C.