Abstract
Given substantial regional differences in absolute humidity across the US and our understanding of the relationship between absolute humidity and influenza, we may expect important differences in regional seasonal influenza activity. Here, we assessed cross-seasonal influenza activity by comparing counts of positive influenza A and B rapid test results during the influenza season versus summer baseline periods for the 2016/2017 and 2017/2018 influenza years. Our analysis indicates significant regional patterns in cross-seasonal influenza activity, with relatively fewer influenza cases during the influenza season compared to summertime baseline periods in humid areas of the US, particularly in Florida and Hawaii. The cross-seasonal ratios vary from year-to-year and influenza type, but the geographic patterning of the ratios is relatively consistent. Mixed-effects regression models indicated absolute humidity during the influenza season was the strongest predictor of cross-seasonal influenza activity, suggesting a relationship between absolute humidity and cross-seasonal influenza activity. There was also evidence that absolute humidity during the summer plays a role, as well. This analysis suggests that spatial variation in seasonal absolute humidity levels may generate important regional differences in seasonal influenza activity and dynamics in the US.
Highlights
Improving our understanding of the seasonal nature of influenza is important since it provides insight into the underlying mechanisms modulating influenza transmission [1,2,3], it likely has important effects on viral evolutionary processes [4,5,6], and because it can illuminate pandemic influenza patterns [7,8,9,10,11]
The associations between influenza and absolute humidity for temperate and tropical regions appear paradoxical, these observations have been reconciled by studies showing a U-shaped relationship between influenza transmission and absolute humidity, with suppressed influenza activity when absolute humidity is at moderate levels [19, 23]
The results indicate that seasonal characteristics of influenza vary across the US, and that this variation is associated with absolute humidity
Summary
Improving our understanding of the seasonal nature of influenza is important since it provides insight into the underlying mechanisms modulating influenza transmission [1,2,3], it likely has important effects on viral evolutionary processes [4,5,6], and because it can illuminate pandemic influenza patterns [7,8,9,10,11]. Cross-seasonal influenza in US laboratory studies indicate that low absolute humidity increases the survival and transmission of influenza [3, 18] which is consistent with annual influenza epidemics that peak during the winter when absolute humidity is near minimal levels in temperate regions [3, 19,20,21]. In subtropical and tropical regions influenza activity tends to peak when absolute humidity is at high levels [16, 19, 22, 23]. The associations between influenza and absolute humidity for temperate and tropical regions appear paradoxical, these observations have been reconciled by studies showing a U-shaped relationship between influenza transmission and absolute humidity, with suppressed influenza activity when absolute humidity is at moderate levels [19, 23]. The mechanisms that link absolute humidity and transmission are not fully understood, and it is possible that additional and confounding factors are responsible for the relationships observed
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
