Skip directly to search Skip directly to A to Z list Skip directly to site content
CDC Home

Current Trends Late Season Influenza Type B Virus Activity -- United States

Despite a decline in levels of overall influenza activity, reports of influenza B virus activity increased during April and May. Influenza B outbreaks in April or May have been reported in California, New Mexico, North Dakota, Oregon, and Wisconsin, including two nursing home outbreaks in Napa and Solano counties, California. These, and two earlier nursing home outbreaks reported from Maine (1) and New York, bring to four the number of influenza B outbreaks in nursing homes reported this season. Other outbreaks in the above states occurred predominately among children.

One outbreak affecting a younger population occurred on the Fort Totten reservation in North Dakota beginning mid-April and continuing for 2 weeks. Absentee rates in the reservation school (grades K-6) peaked at 42%, compared with a normal absentee rate of 10%. All 16 teachers and the school principal also reported influenza-like illness during the outbreak. Records from the reservation clinic showed that patient visits had increased 49% during the outbreak and that almost all the increase was associated with influenza-like illness. During the outbreak, 52% of clinic visits were from patients 9 years of age or younger, and 40% of these involved influenza-like illness. Influenza type B virus was isolated from specimens collected from children with typical influenza during the outbreak.

Since April, 14 states have identified their first influenza type B isolates of the season; 13 states had identified type B isolates before April. Reported by W Freeman, MD, Ft. Totten Reservation, J Pearson, DrPH, Acting State Epidemiologist, North Dakota State Dept of Health; Respective state epidemiologists and laboratory directors; Div of Surveillance and Epidemiologic Studies, Epidemiology Program Office, Statistical Svcs Activity, WHO Collaborating Center for Influenza, Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, CDC, D Streitz, North Dakota State Dept. of Health.

Editorial Note

Editorial Note: The report of late influenza B activity, including several outbreaks, emphasizes the importance of maintaining surveillance programs that include laboratory diagnosis for respiratory virus outbreaks outside the fall and winter months. For example, confirmation of occasional outbreaks throughout the summer months would provide one indicator that the implicated virus strain is likely to have a considerable impact in the next winter season. "Early warning" has occurred in 2 recent years--with isolation of influenza B/Singapore/222/79-like strains during summer 1979 and influenza A/Bangkok/1/79-like strains during summer 1980. Presently available information, however, does not permit any reliable prediction that influenza type B, rather than type A, will be responsible for most influenza infections in the United States next winter. As in other years, monitoring of influenza activity during the next few months in countries with tropical climates (where influenza tends to be endemic) and in the Southern Hemisphere, will also be important in improving knowledge of the virus strain likely to appear in the United States next winter.


  1. CDC. Update: influenza activity--United States, MMWR 1983;32:136-41.

Use of trade names and commercial sources is for identification only and does not imply endorsement by the U.S. Department of Health and Human Services.

References to non-CDC sites on the Internet are provided as a service to MMWR readers and do not constitute or imply endorsement of these organizations or their programs by CDC or the U.S. Department of Health and Human Services. CDC is not responsible for the content of pages found at these sites. URL addresses listed in MMWR were current as of the date of publication.

All MMWR HTML versions of articles are electronic conversions from typeset documents. This conversion might result in character translation or format errors in the HTML version. Users are referred to the electronic PDF version ( and/or the original MMWR paper copy for printable versions of official text, figures, and tables. An original paper copy of this issue can be obtained from the Superintendent of Documents, U.S. Government Printing Office (GPO), Washington, DC 20402-9371; telephone: (202) 512-1800. Contact GPO for current prices.

**Questions or messages regarding errors in formatting should be addressed to The U.S. Government's Official Web PortalDepartment of Health and Human Services
Centers for Disease Control and Prevention   1600 Clifton Road Atlanta, GA 30329-4027, USA
800-CDC-INFO (800-232-4636) TTY: (888) 232-6348 - Contact CDC–INFO
A-Z Index
  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #