Abstract
In the spring term of 1985 there was a protracted outbreak of upper respiratory tract febrile illness consistent with a clinical diagnosis of influenza in a boys' boarding school, which lasted from 23 January to 29 March. Although influenza virus infection was confirmed in 89% of cases in the first half of the term, 53% of the cases which occurred in the second half of the term had no evidence of infection with influenza virus. Between 5 February and 31 March 28 boys presented with skin rashes consistent with a clinical diagnosis of erythema infectiosum; 68% of these were associated with parvovirus B19. Investigation of the cases of clinical influenza with no identified respiratory pathogen revealed a 58% infection rate with B19. B19 DNA was identified in either throat swabs or acute stage bloods of nine pupils with influenza-like symptoms. Cohort studies revealed that 44% of pupils aged 15-16 years were immune before the outbreak compared with only 17% of pupils aged 11-12 years. Infection in the younger group was common and was associated with influenza-like illnesses as well as rashes. Forty-eight per cent of those who did not report any symptoms were also infected with B19.