Influenza epidemics observed in primary care from 1984 to 2017 in France: A decrease in epidemic size over time

Area of Science:

• Epidemiology
• Virology
• Public Health

Background:

• Epidemiological analysis of historical influenza epidemics is crucial for understanding disease evolution and refining control strategies.
• Primary care surveillance data spanning three decades provides valuable insights into influenza epidemic trends and profiles.

Purpose of the Study:

• To analyze trends in influenza epidemics over 33 years using a primary care surveillance system.
• To describe epidemic profiles based on circulating influenza virus subtypes.

Main Methods:

• Utilized weekly influenza-like illness (ILI) incidences from the French Sentinelles network (1984-2017).
• Applied periodic regression to detect influenza epidemics within the time series.
• Determined dominant influenza virus (sub)types using French virology data.

Main Results:

• Detected 33 influenza epidemics affecting 4.1% of the population, with an average duration of 9 weeks.
• Observed a significant decrease in epidemic size (-66 cases/100,000/season) and height (-15 cases/100,000) over time.
• Influenza A(H3N2) was the most common dominant virus, associated with larger epidemics, higher peaks, and older affected individuals.

Conclusions:

• The declining trend in epidemic size and height may be attributed to factors such as increased vaccination, improved hygiene, or viral evolution.
• Further research is necessary to ascertain the impact of these potential factors and inform future influenza preparedness plans.