LASSA FEVER - WEST AFRICA (36): NIGERIA (ONDO)
Posted on 02ND JUL 2018
tagged Lassa Fever, West Africa; Nigeria
Date: Fri 29 Jun 2018
Source: PLoS Currents Outbreaks [edited]
Isere EE, Fatiregun A, Ilesanmi O, Ijarotimi I, Egube B, Adejugbagbe A, Famokun GA. Lessons Learnt from Epidemiological Investigation of Lassa Fever Outbreak in a Southwest State of Nigeria December 2015 to April 2016.
Introduction: An outbreak of Lassa fever (LF) reported and confirmed in Ondo state, Southwest Nigeria in January 2016 was investigated. This paper provides the epidemiology of the LF and lessons learnt from the investigation of the outbreak.
Methods: The incidence management system (IMS) model was used for the outbreak coordination. Cases and deaths were identified through the routine surveillance system using standard definitions for suspected and confirmed cases and deaths respectively. Blood specimens collected from suspect cases were sent for confirmation at a WHO accredited laboratory. Active case search was intensified, and identified contacts of confirmed cases were followed up for the maximum incubation period of the disease. Other public health responses included infection prevention and control, communication and advocacy as well as case management. Data collected were analysed using SPSS 20, by time, place and persons and important lessons drawn were discussed.
Results: We identified 90 suspected LF cases of which 19 were confirmed by the laboratory. More than half (52.6 percent) of the confirmed cases were females with a majority (73.7 percent) in the age group of 15 years and older. The case fatality rate (CFR) of 63.2 percent among the laboratory-confirmed positive cases, where 9 of 19 cases died, was significantly higher compared to the laboratory confirmed negative cases, where 6 of the 65 cases died (CFR; 8.5 percent) p 0.05 and under. There were 287 contacts of the confirmed cases identified, out of which 267 (93.0 percent) completed the follow-up without developing any symptoms, and 2 (0.7 percent) developed symptoms consistent with LF and were confirmed by the laboratory. More than half of the contacts were females (64.5 percent) with most of them (89.2 percent) in the age group of 25 years and older.
Discussion: One key lesson learnt from the investigation was that the confirmed cases were mainly primary cases; hence the need to focus on measures of breaking the chain of transmission in the animal-human interface during Lassa fever epidemic preparedness and response. In addition, the high case fatality rate despite early reporting and investigation suggested the need for a review of the case management policy and structure in the state.
ProMED-mail Rapporteur Mary Marshall
[Interestingly, this study did not find any instances of nosocomial transmission, although there have been cases involving health care workers in other localities in Nigeria this year (2018). Since there were only 2 instances of contact transmission, one of the major conclusions of the study is the need to break the chain of transmission from infected animals (the rodent reservoir) to humans as the main source of exposure to Lassa fever virus. Virus transmission to humans occurs when people are in contact with the reservoir rodent host, the multimammate mouse (_Mastomys natalensis_ and _M. erythroleucus_) and the African wood mouse (_Hylomycus pamfi_) or their excreta, as was likely the situation in these cases. Rodent control has to be undertaken at the village level with individual households employing preventive measures. This requires an extensive and continuous public education effort.
Images of the 3 rodent reservoir hosts of Lassa fever virus can be seen for _Mastomys natalensis_ mouse at https://www.inaturalist.org/taxa/45326-Mastomys-natalensis and _M. erythroleucus_ and _Hylomycus pamfi_ at: http://punchng.com/nigerias-large-rat-population-threatens-lassa-fever-war/. - Mod.TY
Maps of Nigeria: http://www.un.org/Depts/Cartographic/map/profile/nigeria.pdf and Ondo State, Nigeria at http://healthmap.org/promed/p/24841.
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