Individual and Environmental Factors Influencing Influenza Transmission: A Multilevel Analysis.

BACKGROUND

Influenza transmission is influenced by both individual characteristics and community-level drivers. Understanding how these drivers jointly influence transmission is important to predicting outbreaks and guiding influenza prevention strategies. Our study aimed to assess individual and colony-level influences, including vaccination and environmental factors, on influenza transmission in the Hutterite communities.

METHODS

We analyzed data from 3271 individuals in 46 Canadian Hutterite colonies during the 2008 influenza season. Weekly PCR-confirmed Influenza A and B outcomes were examined in relation to demographic, vaccination, geographic, and weather variables using multilevel Bayesian hierarchical models in Integrated Nested Laplace Approximations (INLA), which accounted for colony clustering and temporal autocorrelation.

RESULTS

Of the 3271 participants, 239 (7.3%) had PCR-confirmed influenza (128 Influenza A and 111 Influenza B cases). Older age was found to be protective, especially for Influenza B, while males had slightly lower odds than females. Individual vaccination showed little effect, while colony assignment to influenza vaccination was associated with a lower risk of Influenza A and overall Influenza (A/B). Higher weekly mean temperatures were associated with lower odds of Influenza A but with higher odds of Influenza B. Precipitation showed weak associations, and geographic factors such as elevation and distance to the nearest city suggested possible protective effects, but results were imprecise.

CONCLUSIONS

Our findings suggest that influenza risk in Hutterite colonies is associated with local environmental and geographic characteristics in addition to the individual drivers. Incorporating the community-level environmental setting in influenza surveillance may improve preparedness for future outbreaks.