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Current Trends Influenza -- United States

Influenza update: Influenza activity continues to decline in the United States, as judged by reductions in the proportion of states reporting outbreaks of influenza-like illness (Figure 3), the number of patients with influenza-like illness reported by family physicians (Figure 4), and laboratory reports of influenza virus isolations (1). In recent weeks, influenza type B has been more frequently identified than type A(H1N1), which had previously predominated.

Antigenic analysis of influenza type B viruses: Influenza type B, which has caused outbreaks in some countries in the Northern Hemisphere this winter, including the United States, has generally been poorly inhibited by animal sera to the B/Singapore/222/79 reference strain in hemagglutination-inhibition (HI) tests. A spectrum of different reaction patterns has been observed with recent isolates (Table 4). Most isolates from the United States cannot be distinguished in HI tests from B/USSR/100/83 and B/Norway/1/84, although a few variants like B/Texas/1/84 are distinct. Reported by State and Territorial Laboratory Directors and Epidemiologists; Other Collaborating Laboratories; Physician Reporters of the American Academy of Family Physicians; Statistical Svcs Br, Div of Surveillance and Epidemiologic Studies, Epidemiology Program Office, Computer Systems Office, Statistical Svcs Activity, Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.


  1. CDC. Update: influenza activity--United States. MMWR 1984;33:166-7.

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