INFLUENZA A/USSR/77 (H1N1) ON A UNIVERSITY CAMPUS

An extensive outbreak of influenza caused by A/USSR/77 (H1N1) virus occurred in February, 1978, at the University of Maryland, College Park, Maryland, and the outbreak was studied by virus isolation, serology, clinical questionnaire and outpatient chart review. Among students who returned questionnaires, clinical attack rates were extraordinarily high (73.2% of those ≤23 years of age and 45.7% for those >23 years (p < 0.001)), and rates were higher in students who lived on campus (p < 0.05). Employing the criterion of hemagglutination inhibition titer ≥16, 89.8% of those ≤23 years of age had evidence of infection by March, 1978. Illness was generally mild, and no complications were reported. The extent and rapid spread of this outbreak suggested that only immunoprophyiaxis or rapidly acting control measures such as chemoprophylaxis would be effective in this institutional setting with a highly susceptibie population.