Update: Influenza Activity -- United States and England, 1995-96 Season

In cooperation with the World Health Organization (WHO), its collaborating laboratories, and state and local health departments, CDC conducts surveillance to monitor influenza activity and to detect antigenic changes in the circulating strains of influenza viruses. This report summarizes influenza surveillance activities in the United States and England from September 17 through November 11, 1995.

United States

From October 1 through November 11, state and territorial epidemiologists reported sporadic * influenza activity for greater than or equal to 1 week in 16 states (Alaska, Arizona, Connecticut, Idaho, Kansas, Kentucky, Montana, New Hampshire, New Mexico, New York, Rhode Island, South Carolina, Texas, Utah, West Virginia, and Wyoming) and the District of Columbia. Regional influenza activity was first reported from Alaska during the week ending October 7 and from Montana during the week ending October 28.

From September 27 through November 11, sporadic influenza A virus isolates were reported from 12 states (Alaska, Arizona, Colorado, Florida, Idaho, Montana, New York, Oklahoma, South Carolina, Texas, Washington, and Wisconsin), and influenza B isolates were reported from California, Nebraska, and Utah. Of the 18 isolates confirmed at CDC, one was identified as influenza type B, six as influenza type A(H3N2), and 11 as influenza type A(H1N1). Eight of these isolates were further characterized and found to be closely related to the influenza type A strains included in the 1995-96 influenza vaccine.

England

In England, outbreaks of influenza-like illness (ILI) were reported in two boarding schools during the weeks ending September 23 and October 14. The first outbreak involved approximately 130 (24%) of 550 students; influenza type A(H3N2) was isolated from three of the students. The second outbreak began on October 6, peaked October 9, and involved approximately 200 (40%) of 500 students; influenza type A(H3N2) was isolated from two of the students.

Reported by: Participating state and territorial epidemiologists and state public health laboratory directors. World Health Organization collaborating laboratories. Epidemiology Div, Public Health Laboratory Svcs Communicable Diseases Surveillance Center, London. Influenza Br and WHO Collaborating Center for Surveillance, Epidemiology, and Control of Influenza, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Although the timing, intensity, and geographic distribution of influenza activity can vary substantially, the pattern of activity from September through early November 1995 is typical for this time of year in the Northern Hemisphere. Isolated outbreaks such as those in England are not uncommon during October or November, but widespread influenza activity usually does not begin before December. Even though influenza activity cannot be precisely predicted, all three influenza virus strains -- type A(H3N2), type A(H1N1), and type B -- are expected to circulate in the United States during the 1995-96 season.

In the United States, the optimal period for organized vaccination campaigns for high-risk persons is October through mid-November (1). However, health-care providers should continue to offer vaccine to high-risk persons after mid-November and even after influenza activity has been documented in a community. Because early virologic surveillance has indicated cocirculation of influenza type A and type B viruses and because the antiviral drugs amantadine and rimantadine are effective only against influenza type A, continued use of viral culture and rapid antigen detection throughout the season is particularly important. Amantadine or rimantadine can be used for either treatment or prophylaxis of influenza type A infection. Short-term prophylaxis with one of these drugs may be considered when vaccination is offered to high-risk persons after influenza A outbreaks have been reported in a community (1). Protective levels of antibody develop within 1-2 weeks after vaccination.

Influenza surveillance data are collected weekly from October through April. Sources of data include 1) reports of ILI from state and territorial epidemiologists; 2) the number and proportion of patients seen with ILI reported by a network of approximately 150 sentinel physicians; 3) the proportion of total deaths attributed to pneumonia and influenza reported by the vital statistics offices of 121 U.S. cities; and 4) the number and type of influenza viruses isolated by 68 WHO collaborating laboratories throughout the United States. As the influenza season progresses, these surveillance data collected at CDC will be updated weekly and made available through the CDC voice information system, telephone (404) 332-4551, and the fax information system, telephone (404) 332-4565 (request document number 361100). Information about local influenza activity is available from local and state health departments.

Reference

1. ACIP. Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 1995;44(no. RR-3).

Levels of activity are 1) sporadic -- sporadically occurring influenza-like illness (ILI) or culture-confirmed influenza with no outbreaks detected; 2) regional -- outbreaks of ILI or culture-confirmed influenza in counties with a combined population of <50% of the state's total population; and 3) widespread outbreaks of ILI or culture-confirmed influenza in counties having a combined population of greater than or equal to 50% of the state's total population.

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