Epidemiologic and Clinical Features of Lassa Fever Outbreak in Nigeria, January 1-May 6, 2018

Abstract

Lassa fever (LF) is endemic to Nigeria, where the disease causes substantial rates of illness and death. In this article, we report an analysis of the epidemiologic and clinical aspects of the LF outbreak that occurred in Nigeria during January 1-May 6, 2018. A total of 1,893 cases were reported; 423 were laboratory-confirmed cases, among which 106 deaths were recorded (case-fatality rate 25.1%). Among all confirmed cases, 37 occurred in healthcare workers. The secondary attack rate among 5,001 contacts was 0.56%. Most (80.6%) confirmed cases were reported from 3 states (Edo, Ondo, and Ebonyi). Fatal outcomes were significantly associated with being elderly; no administration of ribavirin; and the presence of a cough, hemorrhaging, and unconsciousness. The findings in this study should lead to further LF research and provide guidance to those preparing to respond to future outbreaks.

Keywords: Lassa fever; Lassa virus; Nigeria; epidemiology; outbreak; ribavirin; viruses.

Figure 1

Geographic and temporal distribution of laboratory-confirmed Lassa fever cases, Nigeria, January 1–May 6, 2018. A) Geographic distribution of laboratory-confirmed cases by state. Gray shading indicates states reporting no laboratory-confirmed cases. Locations of Lassa fever treatment centers are indicated. B) Epidemic curve of laboratory-confirmed Lassa fever cases. Epidemiologic week numbers are based on the date of symptom onset.

Figure 2

Exposure history and case-fatality rate among patients with laboratory-confirmed Lassa fever cases, Nigeria, January 1–May 6, 2018. A) Proportion of persons reporting Lassa fever exposure risks for all case-patients, HCWs, and non–HCWs. To assess differences in exposure risks between HCWs and non–HCWs, p values were calculated by using the χ² test and adjusted by the Bonferroni correction. B) The case-fatality rate for case-patients who did or did not receive ribavirin. C) An investigation of the case-fatality rate in patients who survived >7 days after symptom onset. For panels B and C, p values were calculated by using binomial logistic regression analysis adjusted for age and sex and applying the Bonferroni correction. HCW, healthcare worker.