An outbreak of infectious mononucleosis among the personnel of an outpatient clinic.

During a four-week period, nine current or recent primary Epstein-Barr virus (EBV) infections were identified among 29 staff members of an obstetrics and gynecology outpatient clinic of an air force base hospital by EBV-specific serologic tests; i.e., early detection of IgM antibodies to EB viral capsid antigen (VCA), high titers of IgG antibodies to VCA, presence of antibodies to the D (diffuse) component of the EBV-induced early antigen (EA) complex and initial absence and later development of antibodies to the EBV-associated nuclear antigen (EBNA). Five of these individuals showed classical signs and symptoms of infectious mononucleosis (IM) so that the ratio between overt and silent infections was 1.25:1. All but one of these nine individuals gave positive monospot reactions. Three additional staff members were reported to be monospot-positive, of whom two, with prior histories of IM, had IM-like illnesses during the study period but the results of EBV-specific serologic tests were indicative of infections in the past. The EBV infections were limited to the nurses, corpsmen and administrative personnel, of whom none remained susceptible (antibody negative). The virus did not spread to the medical staff although two of the residents had no antibodies to EBV. The data indicate that under some circumstances IM may be more contagious than usually observed.