Lassa fever outbreaks have been confirmed across five West African countries, including Nigeria, Benin, Sierra Leone, Togo, and Burkina Faso.
In Nigeria, the index case emerged on 16 December 2016 in Ogun state. Since then, the outbreak has remained active. During the week ending 19 March 2017), 15 suspected cases were reported, with two testing positive for Lassa fever.
Between 16 December 2016 and 19 March 2017, a total of 283 suspected cases including 56 deaths (case fatality rate of 19.8%) have been reported. Of the suspected cases, 99 were confirmed by the Lagos University Teaching Hospital Lassa laboratory in Nigeria.
The cases have been distributed across 13 states: Ogun, Bauchi, Plateau, Ebonyi, Ondo, Edo, Taraba, Nasarawa, Rivers, Kaduna, Gombe, Cross-River and Borno.
The outbreak of Lassa fever in Benin started on 12 February 2017 from Tchaourou district, Borgou province, close to the border with Nigeria. It was established that this case had epidemiological link with the ongoing Lassa fever outbreak in Nigeria. On 23 February 2017, another suspected case from L’Atacora province was reported.
Samples obtained from the two cases tested positive for Lassa fever in the laboratory in Cotonou, Benin and in the Lagos University Teaching Hospital Lassa laboratory. Both cases died, giving a case fatality of 100%.
In Togo, Lassa fever was confirmed on 23 February 2017, with the case having established epidemiological linkage to Benin. A total of 12 suspected were subsequently reported, seven of them were confirmed at the Institut National d’Hygiène in Lomé, Togo. Four of the confirmed cases died, giving a case fatality rate of 57%. The cases originated from Oti and Kpendjal districts.
On 26 February 2017, the Ministry of Health of Burkina Faso notified WHO of a confirmed Lassa fever case admitted in a hospital in the northern part of Togo. The case originated from Ouargaye district, central eastern part of Burkina Faso. Burkina Faso has not had any other case.
Sierra Leone has been reporting sporadic suspected cases of Lassa fever since 28 December 2016. However, the outbreak situation escalated in the months of February and March 2017 when a cluster of 24 cases were reported and investigated. Out of these, four cases were laboratory confirmed and all of them died, thus giving case fatality rate of 100% among the confirmed. The outbreak has since subsided.
Lassa fever is endemic in Nigeria and other West African countries. Outbreaks have occurred almost every year in different parts of the region, with yearly peaks observed between December and February.