Current Trends Update: Influenza -- United States, 1988-89 Season

As of January 13, 1989, 186 culture-confirmed cases of influenza in the United States had been reported to CDC. One hundred fifty (81%) of these were influenza type B viruses, 28 (15%) were type A(H1N1), and eight (4%) were type A(H3N2).

Age was reported for 99 of the persons with type B influenza. Although these cases occurred in persons aged 5 months to 77 years, 55 (56%) of these persons were less than or equal to18 years of age. These viruses were reported from 23 states (Figure 1) and were implicated as the etiologic agent in four of the five culture-confirmed influenza outbreaks reported since mid-November. These four outbreaks occurred in elementary schools in Ohio, Nebraska, California, and Washington, where maximum absenteeism levels during the outbreaks ranged from 14% to 36%.

The 28 influenza A(H1N1) viruses were reported from 11 states (Arizona, California, Colorado, Hawaii, Illinois, Ohio, Massachusetts, New York, Minnesota, Washington, and Wisconsin). The only outbreak associated with these viruses occurred at a Wisconsin university in December. During the outbreak's peak, approximately 25% of persons seen at the outpatient student clinic had an influenza-like illness; seven isolates of influenza A(H1N1) virus were recovered from 17 specimens tested from these students.

Four states (Florida, Hawaii, New York, and Pennsylvania) and the District of Columbia reported influenza A(H3N2) viruses but no outbreaks. Reported by: Participating state and territorial epidemiologists and state laboratory directors. WHO Collaborating Laboratories. Sentinel Physicians of the American Academy of Family Physicians. Influenza Research Center, Baylor College of Medicine, Houston, Texas. Div of Surveillance and Epidemiologic Studies, Epidemiology Program Office; WHO Collaborating Center for Influenza, Influenza Br, and Epidemiology Office, Div of Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: During the 1987-88 influenza season, influenza A(H3N2) predominated, and influenza B appeared late (1). In contrast, influenza B has predominated during the 1988-89 influenza season, with most reported illnesses occurring in children. The impact that this year's influenza B activity will have on older persons and persons at high risk of serious complications or death is unknown. However, excess mortality has occurred in each of the influenza B epidemics since 1979 (2-4). Thus, efforts to immunize high-risk persons in all age groups should continue even as outbreaks begin (5).

An increased risk for Reye syndrome in children and teenagers when aspirin is used to treat influenza symptoms has been reported in years when type B influenza has predominated (6,7). Parents, teenagers and children who self-medicate, and health-care workers should be aware of this possible serious complication associated with aspirin use.

Amantadine, which may be indicated for prophylaxis or treatment of influenza A, is not effective against influenza B (5). Thus, during seasons such as this, when both influenza A and B strains circulate, virus cultures need to be obtained during outbreaks of influenza-like illness to assess the appropriateness of amantadine therapy.

A recorded message on U.S. influenza activity is now available 24 hours a day. This message is updated weekly by CDC and can be accessed at (404) 332-4551.

References

1. CDC. Influenza--United States, 1987-88 season. MMWR 1988;37:497-503. 2.Nolan TF Jr, Goodman RA, Hinman AR, Noble GR, Kendal AP, Thacker SB. Morbidity and mortality associated with influenza B in the United States, 1979-1980: a report from the Center for Disease Control. J Infect Dis 1980;142:360-2. 3.Lui KJ, Kendal AP. Impact of influenza epidemics on mortality in the United States from October 1972 to May 1985. Am J Public Health 1987;77:712-6. 4.CDC. Influenza--United States, 1985-1986 season. MMWR 1986;35:470,475-9. 5.ACIP. Prevention and control of influenza. MMWR 1988;37:361-73. 6.Hurwitz ES, Barrett MJ, Bregman D, et al. Public Health Service study of Reye's syndrome and medications: report of the main study. JAMA 1987;257:1905-11. 7.CDC. Reye syndrome surveillance--United States, 1986. MMWR 1987;36:689-91.

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