Correlation of the basic reproduction number (R(0)) and eco-environmental variables in Colombian municipalities with chikungunya outbreaks during 2014-2016

Chikungunya virus (CHIKV) emerged in Colombia in 2014 into a population presumed fully susceptible. This resulted in a quick and intense spread across Colombia, resulting in an epidemic that affected an estimated 450,000 people. The reported Colombian cases accounted for over 49% of all the cases reported to the PAHO. Eco-environmental factors are known to be associated with the spread of arboviruses such as CHIKV, and likely contribute to the differences in transmission profiles that were observed across several municipalities. To determine the association of eco-environmental factors and CHIKV, the basic reproduction number (R(0)) in 85 municipalities, which accounted for 65.6% of reported CHIKV cases in Colombia, was estimated. Estimates of R(0) ranged from 1 to 9, where over 76% of municipalities had R(0) values between 1 and 2. When we looked at the distribution of R(0), the cumulative proportions were 20% with R(0)>2, 14% with R(0)>3, and 9% with R(0)>4. Next, we determined that there were different patterns of correlation between environmental and/or ecological variables and R(0) when we considered different R(0) lower-thresholds. Broadly, we found that temperature-related variables are significantly and positively correlated to R(0) regardless of the lower threshold, while other variables like duration of outbreak and size of the urban area are inversely related to R(0). Specifically, we conclude that high values of temperature-related variables where R(0) > 1 will result in a fast growth of cases in a shorter time period (with faster cessation of outbreak transmission) but will result overall in a fewer total cases compared to outbreak areas (R(0) > 1, but classified as lower). Thus, in the absence of vector control, a less explosive outbreak may be more advantageous for the virus in terms of transmission.