Prognosis

The overall case fatality rate among people infected with Lassa virus is 1%; however, the observed case fatality rate among patients hospitalised with Lassa fever has been reported to be between 15% and 70%, with higher numbers reported during large outbreaks (50%), or in patients presenting to a Lassa fever hospital with a positive Lassa antigen test (65% to 70%).[2][9] The case fatality rate in the 2016 outbreak in Nigeria was 59.6%, with the rate increasing to 100% in children aged 5 years or younger and adults aged 55 years or older.[44] The case fatality rate in children admitted to one hospital in Sierra Leone was 27%, and a higher mortality was seen in those aged <29 years compared with those aged >29 years.[3][12]

Lassa fever can be especially severe in late pregnancy, with maternal death and/or fetal loss occurring in more than 80% of cases during the third trimester.[5]

Although there is little evidence, it has been suspected that patients can excrete virus in their urine for between 3 and 9 weeks after disease onset, and in semen for up to 3 months; therefore, it has been recommended that sexual intercourse should be avoided until 3 months following recovery.[8]

Death usually occurs within 14 days of onset in fatal cases.

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