Large-scale Lassa fever outbreaks in Nigeria: quantifying the association between disease reproduction number and local rainfall

Shi Zhao; Salihu S. Musa; Hao Fu; Daihai He; Jing Qin

LF epidemics typically start in November and last until May of the following year, with the majority of cases occurring in the first quarter of the following year, in addition to sporadic cases reported throughout the year. The 2017-18 epidemic in Nigeria was an unprecedented LF outbreak in the country's history [11] , which resulted in 400 confirmed cases, including 97 deaths, between January and March 2018 [12] . The 2018-19 epidemic in Nigeria has already caused 420 confirmed cases from January to March 02 of 2019, which included 93 deaths [12] . The five states of Edo, Ondo, Ebonyi, Bauchi, and Plateau are the only states that have been among the top 10 hit hardest states in terms of number of LF cases in both the 2018 (85.5% of total national cases) and 2019 (85.7% of total national cases) outbreaks. While there have been discussions about the connection of rainfall to LF [13, 14] , this connection has not yet been demonstrated and quantified. This work aims to study the epidemiological features of outbreaks in different Nigerian regions between January 2016 and March 2019. We estimate LF infectivity in terms of the reproduction number (R) and quantify the association between R and local rainfall by using modeling analysis. We explore the spatial heterogeneity of the LF outbreaks and summarize the overall findings with model-average estimates.