Generalized viral illness caused by an intermediate strain of adenovirus (21/H21 + 35).

Ten isolates of an antigenically intermediate strain of adenovirus were recovered from eight persons who presented febrile upper respiratory illness, pneumonia, or multisystem disease between November 1976 and August 1978. Six isolates were recovered from four members of an extended family in which the other nine members all had serologic evidence of infection; the other four isolates were epidemiologically unrelated. The isolates were placed in hemagglutination group IB on the basis of results of differential hemagglutination tests. All isolates were identified as adenovirus 21 by serum-neutralization tests and as types 21, 34, or 35 by hemagglutination-inhibition tests with reference rabbit and horse antisera. Conversely, rabbit antiserum to the intermediate strain had high titers of neutralizing antibody to adenovirus 21 and high titers of hemagglutination-inhibiting antibody to adenoviruses 21 and 35. The patients' serologic responses were similar. Thus, the isolates were typed as adenovirus 21/H21 + 35 and are the first such intermediate strains recorded.