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 less than or equal to 23 years of age and 45.7% for those greater than 23 years (p less than 0.001)), and rates were higher in students who lived on campus (p less than 0.05). Employing the criterion of hemagglutination inhibition titer greater than or equal to 16, 89.8% of those less than or equal to 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 immunoprophylaxis or rapidly acting control measures such as chemoprophylaxis would be effective in this institutional setting with a highly susceptible population.