title: The sensitivity and specificity of Lassa virus IgM by ELISA as screening tool at early phase of Lassa fever infection.
abstract: BACKGROUND
  Early diagnosis, prompt treatment, and disease containment are vital measures in the management of Lassa fever (LF), a lethal and contagious arenaviral hemorrhagic disease prevalent in West Africa. Lassa Virus (LAV)-specific Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) test, the gold standard for diagnosis, is unavailable in most centers. Serologic detection of LAV IgM is a more accessible tool and this work was to investigate its adequacy as an early marker for LF.
  
  
  METHODS
  A prospective case-control study conducted July 2007-March 2011 in a tertiary referral health center in Nigeria. Blood samples for test and control were evaluated for Lassa specific antigens and IgM using RT-PCR (primers S36+ and LVS 339) and indirect ELISA (Lassa Nucleo-protein (NP)-Antigen) respectively. RT-PCR outcome was used as standard to test for the sensitivity and specificity of IgM.
  
  
  RESULTS
  Of the 37 confirmed cases of LF infection by RT-PCR, 21 (57%) were IgM positive. Amongst the 35 confirmed negative cases (control group), eight were IgM positive. The diagnostic sensitivity and specificity of the IgM assay were 57% and 77% respectively. The negative and positive predictive values of the IgM serological assay were 63% and 72%, respectively, while the efficiency of the test was 67%.
  
  
  CONCLUSIONS
  The specificity and sensitivity of IgM as a screening tool for early detection of LF appear weak and, hence, the need for a reliable LF "rapid screening kit" since RT-PCR is unavailable in most centers. In the interim, "high clinical index of suspicion," irrespective of IgM status, requires urgent referral to confirmatory centers.
authors: The Research Unit, Lassa Fever Research and Diagnostic Centre, Irrua Specialist Teaching Hospital, Irrua, Nigeria ; Department of Ear, Nose, and Throat, College of Health Sciences, University of Abuja, Nigeria.
authors: Titus S
authors: TS
authors: Ibekwe
authors: Maxwell M
authors: MM
authors: Nwegbu
authors: Daniel
authors: D
authors: Asogun
authors: Donatus I
authors: DI
authors: Adomeh
authors: Peter O
authors: PO
authors: Okokhere
keywords: Immunoglobulin M; Lassa fever; reverse transcriptase polymerase chain reaction test; serology
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