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Update: influenza activity--worldwide, May-September 1999
Insights
Global influenza surveillance from May to September 1999 showed moderate to severe activity, primarily driven by Influenza A(H3N2) viruses. This report details worldwide trends and antigenic changes in circulating influenza strains.
Area of Science:
- Virology
- Epidemiology
- Public Health
Background:
- The Centers for Disease Control and Prevention (CDC) collaborates with global health organizations to monitor influenza.
- Surveillance is crucial for tracking influenza virus activity and detecting antigenic drift.
Purpose of the Study:
- To summarize global influenza activity from May to September 1999.
- To analyze the antigenic characteristics of influenza virus isolates collected during May-August 1999.
Main Methods:
- Global influenza surveillance data collection through the WHO network of collaborating laboratories.
- Analysis of antigenic characteristics of isolated influenza viruses.
Main Results:
- Influenza activity was moderate to severe in the Northern Hemisphere from October 1998 to April 1999, with Influenza A(H3N2) predominating.
- Influenza type B viruses were more frequent than Influenza A in some countries, while Influenza A(H1N1) caused sporadic cases and outbreaks.
- Influenza activity in the Southern Hemisphere (May-September 1999) peaked and declined, primarily associated with Influenza A(H3N2) viruses.
Conclusions:
- Influenza A(H3N2) viruses were the predominant cause of global influenza during the reported period.
- Continued surveillance is essential for understanding influenza epidemiology and informing public health strategies.
Abstract:
In collaboration with the World Health Organization (WHO), the WHO international network of 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. From October 1998 through April 1999, influenza activity was moderate to severe in the Northern Hemisphere. Influenza A(H3N2) viruses predominated but influenza type B viruses were isolated more frequently than influenza A in some countries. Influenza A(H1N1) viruses were isolated from sporadic cases in Asia, Europe, and North America, and from outbreaks in South America. Since May 1999, influenza activity associated primarily with influenza A(H3N2) viruses has peaked and is declining in the Southern Hemisphere. This report summarizes worldwide influenza activity during May-September 1999 and the antigenic characteristics of influenza isolates collected during May-August 1999.