Hepatitis A outbreak in an institution

In February 1996, four serologically confirmed cases of hepatitis A virus (HAV) occurred in one household. Investigation showed that the source was a family member with sub-clinical HAV who attended a Unit for Learning Disabilities. Reports of two further cases in the institution followed and control measures were instigated. Contacts were unwilling to accept human normal immunoglobulin (HNIG). Following salivary antibody and serological testing, hepatitis A vaccine was offered to the non-immune. An investigation found that sub-clinical infection was significantly associated with being less than 5 years old (RR = 6.07, p < 0.005) and being in one particular classroom (RR = 6.21, p < 0.0005). None of the staff in the institution became infected. In all, 31 cases of hepatitis A (18 clinical and 13 subclinical cases) occurred. This paper (a) describes an outbreak of hepatitis A (b) refers to the use of a salivary antibody test (assay performance to be published elsewhere) (c) identifies factors associated with the acquisition of HAV and (d) endeavours to assess the effectiveness of the vaccine to contain the outbreak.