Update: influenza activity--United States and worldwide, May-October 2004

Area of Science:

• Virology
• Epidemiology
• Public Health

Background:

• Influenza viruses, including Influenza A (H3N2), A (H1N1), and B, are significant global respiratory pathogens.
• Understanding seasonal influenza activity is crucial for public health preparedness and response.

Purpose of the Study:

• To summarize global and United States influenza activity from May to October 2004.
• To describe the prevalence of different influenza virus strains during this period.

Main Methods:

• Surveillance data collection on influenza virus isolates.
• Analysis of reported influenza activity levels worldwide and in North America.

Main Results:

• Influenza A (H3N2) viruses were the predominant strain circulating globally between May and October 2004.
• These viruses were associated with mild-to-moderate disease activity.
• Influenza A (H1N1) and B viruses were reported less frequently worldwide.
• In North America, all three types (A (H3N2), A (H1N1), and B) were identified sporadically.
• This period represented the inter-epidemic phase, preceding the typical North American winter peak.

Conclusions:

• Influenza A (H3N2) was the dominant influenza strain globally during the May-October 2004 surveillance period.
• Sporadic activity of multiple influenza strains occurred in North America, with lower overall activity preceding the winter season.