EPIDEMIOLOGICAL CHARACTERISTICS OF LASSA FEVER IN SIERRA LEONE, 2018 TO 2022: A RETROSPECTIVE ANALYSIS OF NATIONAL SURVEILLANCE DATA

Abstract

Background: The Eastern region of Sierra Leone is known to be endemic to Lassa fever. However, in recent years there has been an observed geographical shift in the disease epidemiology with frequent outbreaks reported in non-endemic regions of the country. This study aims to describe the epidemiological characteristics of reported Lassa fever cases in Sierra Leone from 2018 – 2022.

Methods: A retrospective analysis of Lassa fever cases reported from January 2018 to December 2022 was carried out. We extracted data from the National Reference Laboratory/surveillance database to compute descriptive analysis on key variables including age, sex, and districts. Frequencies, proportions, and rates were computed.

Result: A total of 1,127 suspected and 63 confirmed cases of Lassa fever with 40 deaths (CFR-63%) were reported. Of the confirmed cases, the median age was 19 years (range: 1 to 82 years); females accounted for 57% (36/63), and the age group ≤9 years accounted for the highest, 40% (25/63). The average number of confirmed cases reported per year was 13, with the lowest, 8 cases reported in 2020 and the highest, 16 reported in 2021. The cumulative incidence rate was 1 per 100,000 populations. Kenema district accounted for 81% (51/63), followed by Tonkolili and Bo Districts with 10% (6/63) and 5% (3/63) respectively. The peak of infection was in 2021 with 25% (16/63) cases.

Conclusion: The trend of Lassa fever cases was almost constant for the period under study. Kenema District accounted for most Lassa fever cases and persons aged 20 – 29 years accounted for the highest incidence. We recommend the Ministry of Health to conduct community sensitizations to improve early health-seeking behavior in high-incidence districts and intensify community-based surveillance.

Keywords: Lassa fever, hemorrhagic, Sierra Leone, Kenema.