Evaluation of an indirect immunofluorescence assay for detection of IgM (IF-IgM) type antibodies in the early diagnosis of leptospirosis

Abstract

Introduction: leptospirosis is a severe febrile disease, with a variety of clinical presentations. This results in the delay of clinical diagnosis, or in difficulties achieving it, so having the appropriate laboratory tests may deem useful to guide the initial care of these patients.
Objective: to evaluate a self-made immunofluorescence technique for the detection of IgM antibodies (IF-IgM) in the early diagnosis of leptospirosis.
Method: serum samples obtained from patients with a clinical suspicion of leptospirosis were analysed by IF-IgM antibodies and the microagglutination test (MAT) . Sensitivity and specificity of IF-IgM versus MAT were determined using a double entry table. Agreement between two observers was determined by the Kappa test.
Results: out of one hundred and sixty one early samples analysed, 97 serum samples corresponded to patients with a confirmed acute infection by MAT and 64 evidenced no infection. Sensitivity and specificity of IF-IgM assays in the acute phase were 79% and 100% respectively. The Kappa value was 1.
Conclusions: IF-IgM seems to be a useful tool for the early diagnosis of patients with leptospirosis. It does not need viable bacteria to be handled; it may be applied in laboratories equipped with ultraviolet light microscopes, a single serum sample is needed and the result is seen three to four hours later. As to its disadvantages, it fails to identify the involved serovars and a negative result does not discard infection. Bearing the latter into account, the MAT test is mandatory in a second serum sample obtained 10-20 days after the first one, to either discard or confirm the disease.