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 Disabi lities. Reports of two further cases in the institution followed and contro l 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 th an 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) occurre d This paper (a) describes an outbreak of hepatitis A (b) refers to the use o f a salivary antibody test (assay performance to be published elsewhere) (c ) identifies factors associated with the acquisition of HAV and (d) endeavo urs to assess the effectiveness of the vaccine to contain the outbreak.