INFLUENZA B VIRUS INFECTIONS IN THE COMMUNITY AND THE FAMILY

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Abstract
Frank, A. L. (Baylor College of Medicine, Houston, TX 77030), L. H. Taber, W. P. Glezen, E. A. Geyer, S. Mcllwain and A. Paredes. Influenza B virus infections in the community and the family: the epidemics of 1976–1977 and 1979–1980 in Houston, Texas. Am J Epidemiol 1983; 118: 313–25. Influenza B virus epidemics occurred in Houston, Texas, in 1976–1977 and 1979–1980. Among families with young children followed longitudinally in the Houston Family Study, 112 infections were detected during 511 person-years of observation. The infection rates for the two epidemics were similar—24 per cent and 20 per cent—although the two epidemics differed greatly in the community. The first epidemic was much more intense with a mid-winter peak that produced school absentee rates above 12 per cent for four consecutive weeks. The indolent epidemic of 1979–1980 smoldered from late September to mid-April with a peak during the second week of March for which school absenteeism did not exceed 8 per cent. In the Houston Family Study population, the combined infection rate for the two outbreaks was highest at 35 per 100 person-years for school children aged 6–19 years. Preschool children aged 7 months-5 years and adults had infection rates of 31 and 16 per 100 person-years, respectively. Preexisting neutralizing antibody titers ⩾3.5 log2 protected against influenza B infection and illness. Preschool children above 6 months of age, school age children, and parents introduced infection into the family at rates of 15, 15, and 9 per 100 person-years, respectively. Three second introductions were observed. The secondary infection rate was highest among school aged children at 61 per 100 persons at risk.