Analysis of sociodemographic and clinical factors associated with Lassa fever disease and mortality in Nigeria

Abstract

Over past decades, there has been increasing geographical spread of Lassa fever (LF) cases across Nigeria and other countries in West Africa. This increase has been associated with significant morbidity and mortality despite increasing focus on the disease by both local and international scientists. Many of these studies on LF have been limited to few specialised centres in the country. This study was done to identify sociodemographic and clinical predictors of LF disease and related deaths across Nigeria. We analysed retrospective surveillance data on suspected LF cases collected during January-June 2018 and 2019. Multivariable logistic regression analyses were used to identify the factors independently associated with laboratory–confirmed LF diagnosis, and with LF–related deaths. There were confirmed 815 of 1991 suspected LF cases with complete records during this period. Of these, 724/815 confirmed cases had known clinical outcomes, of whom 100 died. LF confirmation was associated with presentation of gastrointestinal tract (aOR 3.47, 95% CI: 2.79–4.32), ear, nose and throat (aOR 2.73, 95% CI: 1.80–4.15), general systemic (aOR 2.12, 95% CI: 1.65–2.70) and chest/respiratory (aOR 1.71, 95% CI: 1.28–2.29) symptoms. Other factors were being male (aOR 1.32, 95% CI: 1.06–1.63), doing business/trading (aOR 2.16, 95% CI: 1.47–3.16) and farming (aOR 1.73, 95% CI: 1.12–2.68). Factors associated with LF mortality were a one-year increase in age (aOR 1.03, 95% CI: 1.01–1.04), bleeding (aOR 2.07, 95% CI: 1.07–4.00), and central nervous manifestations (aOR 5.02, 95% CI: 3.12–10.16). Diverse factors were associated with both LF disease and related death. A closer look at patterns of clinical variables would be helpful to support early detection and management of cases. The findings would also be useful for planning preparedness and response interventions against LF in the country and region.

An Epidemiological Analysis of Lassa Fever Outbreak in Nigeria from January 2019 to June 2023

“…"Variables presumed to be potentially associated with both outcome variables were identified based on evidence in the literature and biological plausibility" [1].…”

“…"Any individual presenting with one or more of the following: malaise, fever, headache, sore throat, cough, nausea, vomiting, diarrhea, myalgia, chest pain, hearing loss and either; (a) history of contact with excreta or urine of rodents and (b) history of contact with a probable or confirmed Lassa fever case within a period of 21 days of onset of symptoms or any person with inexplicable bleeding/hemorrhagic" [1].…”

“…"Any suspected case (see definition above) who died or absconded without collection of specimen for laboratory testing". [1] 1.1.6 Definition 6 (contact) "Anyone who has been exposed to an infected person, or to an infected person's secretions, excretions, or tissues within three weeks of last contact with a confirmed or probable case of Lassa fever". [1]…”

“…Delay in LF diagnosis often occurs because of non-specific symptoms such as fever and the assumption that the febrile illness is caused by other factors, especially malaria that is endemic in sub-Saharan Africa. Identifying the onset of the disease is often difficult due to the generalized symptoms and clinical presentation such as fever, vomiting, fatigue, abdominal pain, sore throat, chest pain and myalgia" [1].…”

“…"Lassa fever (LF) is a viral hemorrhagic disease transmitted from infected rodents to humans or through humanto-human contacts" [1]. "Generally, animal-to-human transmission occurs following exposure to rodent excreta and secretions (urine and saliva) while human-to-human transmission occurs via contact with body fluids of an infected person and is related to poor infection control practices" [1]. "Historical data indicate that LF is endemic in West African countries of Nigeria, Sierra Leone, Liberia, Benin and Guinea, with sporadic cases occurring elsewhere in the region" [2].…”