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Current Trends Influenza Surveillance Summary, 1981-1982 Season

National data on influenza activity for the 1981-1982 season were obtained from three major sources: (a) weekly reports of mortality from 121 cities, including the ratio of pneumonia and influenza (P and

  1. deaths to total deaths, an index of the relative mortality attributable to influenza; (b) weekly reports of the number of respiratory specimens tested and the number and types of influenza isolates identified by 63 collaborating state, county, city, or military laboratories, and (c) weekly semi-quantitative estimates from each state health department of the extent of influenza-like morbidity indicated by their individual statewide surveillance systems. In addition, spontaneous reports of unusual cases and outbreaks of influenza were received by CDC.

In terms of all the available criteria, the impact of influenza was low in the 1981-1982 season. Mortality statistics did not show a national increase in the ratio of deaths associated with P and I beyond the expected seasonal variation (Figure 1), despite presence of virus through May 1982 (Figure 2); widespread influenza activity was reported in only four states throughout the period of virus circulation (Figure 3). In the preceding season, by way of contrast, the ratio of P and I deaths to total deaths was elevated for 13 weeks, and 32 states reported widespread influenza activity. Both influenza type B and influenza type A(H1N1) viruses were commonly isolated during the 1981-1982 season, but the total number of isolates reported to CDC by collaborating laboratories was approximately 600, compared with a range of 1,000 to 2,000 in the 5 preceding years (Figure 4).

Of the isolates obtained by the collaborating laboratories, 74% were influenza type B virus; 23 states isolated only influenza type B virus. Seventeen states isolated both influenza B and influenza A(H1N1) viruses, and one state isolated only influenza A(H1N1) virus. Influenza B virus outbreaks were first detected during the season in the southwestern states beginning January to February, then spread east and north. By the end of the season, influenza B had been identified in almost all regions of the country (Figures 5, 6). Throughout the winter, influenza A(H1N1) virus was more prevalent in the southwestern and Pacific regions than elsewhere, although some activity was detected in the eastern regions. Only a few influenza A(H3N2) strains, associated with sporadic cases in Florida and Texas, were isolated from residents of the continental United States during the 1981-1982 season. In Nevada swine influenza-like virus was isolated from an immunocompromised child (1).

The predominant influenza B and influenza A(H1N1) viruses were frequently associated with reports of widely separated outbreaks among school children--typically with little evidence of community-wide impact, as judged by minimal increases in absenteeism for entire school districts and by lack of increases in numbers of hospital emergency room visits for influenza-like illness. From about March through May, occasional outbreaks of influenza B virus in nursing homes were documented. Reported by Immunization Div, Center for Prevention Svcs, Consolidated Surveillance and Communications Activity, Epidemiology Program Office, Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

Reference

  1. CDC. Swine influenza-like isolate--Nevada. MMWR 1982;31:195.

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