A review of Lassa fever outbreaks in Nigeria From 1969 to 2017: Epidemiologic profile, determinants and public health response

Introduction: Lassa fever outbreaks have occurred in Nigeria since the 1969 till date. This is in spite of the fact that the reservoir and modes of transmission have been known for all these years. This review aimed at describing the epidemiology and determinants of the Lassa fever outbreaks in Nigeria from 1969 to 2017 and the public health response to these outbreaks.Method: The guidelines for the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) were used to conduct the review between May 2017 and January, 2018. We searched PubMed, Science direct, WHO library databases and Google Scholar for articles published from 1970 till January 2018. Other relevant websites such as those of the World Health Organization, Nigeria Centers for Disease Control and Prevention were searched for Lassa fever outbreak reports.Results: Twenty-six articles and reports were included in the final review. These described twenty-one outbreaks involving 5442 suspect cases, 768 confirmed cases and 631 deaths from suspected or confirmed Lassa fever. Thirty-two states and the Federal Capital Territory have ever recorded outbreaks of Lassa fever. Lassa fever cases now occur in various states in Nigeria all year round with dry season peaks. Nosocomial transmission has remained a consistent determinant. Public health responses have changed over time starting from predominantly case management in initial outbreaks to a centrally coordinated response supporting states and institutions over the years.Conclusion; Lassa fever outbreaks have increased in frequency and geographic spread with case fatality ratio remaining unacceptably high. The same determinants have persisted with nosocomial transmission a consistent factor. Public health response has consistently improved with the last two years showing the most coordinated response. We recommend that the definition of Lassa fever in the Nigerian Integrated Disease Surveillance and Notification System (IDSR) be revised to reflect the current reality to ensure better Lassa fever control.Key words: Lassa fever, Outbreak, Viral haemorrhagic fevers, Nigeria