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Update: influenza activity--United States, 1998-99 season
Insights
Influenza activity increased in the US starting mid-January 1999. Vaccine effectiveness against circulating influenza A(H3N2) viruses was estimated in a long-term-care facility outbreak investigation.
Area of Science:
- Public Health
- Epidemiology
- Virology
Background:
- Influenza surveillance data from October 4, 1998, through February 27, 1999, is summarized.
- An influenza outbreak investigation was conducted in a long-term-care facility (LTCF).
Purpose of the Study:
- To summarize national influenza activity during the 1998-99 season.
- To investigate an influenza outbreak in an LTCF.
- To estimate 1998-99 influenza vaccine effectiveness against circulating influenza A(H3N2) viruses.
Main Methods:
- Analysis of national influenza surveillance data.
- Outbreak investigation including case ascertainment and data collection within an LTCF.
- Calculation of vaccine effectiveness using data from the LTCF.
Main Results:
- Influenza activity in the US began increasing in mid-January 1999.
- Elevated influenza activity persisted in most US regions through February 27, 1999.
- Influenza A(H3N2) viruses were circulating and vaccine effectiveness was estimated at the LTCF.
Conclusions:
- The 1998-99 influenza season saw a significant increase in activity starting mid-January.
- LTCFs are vulnerable to influenza outbreaks, necessitating ongoing surveillance and vaccination efforts.
- Vaccine effectiveness estimates provide crucial data for public health interventions during influenza seasons.
Abstract:
This report summarizes influenza activity in the United States from October 4, 1998, through February 27, 1999. It also presents results of an investigation of an influenza outbreak among staff and residents at one long-term-care facility (LTCF), and estimates the 1998-99 influenza vaccine effectiveness against the circulating influenza A(H3N2) viruses at that facility. Based on influenza surveillance data, influenza activity in the United States began to increase in mid-January 1999 and remained elevated in most regions of the country through the week ending February 27.