International multicenter evaluation of the clinical utility of a dipstickassay for detection of Leptospira-specific immunoglobulin M antibodies in human serum specimens

We performed a multicenter evaluation of a robust and easily performed dips tick assay for the serodiagnosis of human leptospirosis. The assay is aimed at the detection of Leptospira-specific immunoglobulin M (IgM) antibodies. The study involved 2,665 serum samples collected from 2,057 patients with suspected leptospirosis in 12 countries on five continents with different l evels of endemicity and different surveillance systems. The patients were g rouped as laboratory-confirmed leptospirosis case patients and noncase pati ents based on the results of culturing and the microscopic agglutination te st. Paired samples from 27.7% of the subjects were tested. Of the 485 case patients, 87.4% had a positive dipstick result for one or more samples. Of the 1,513 noncase patients, only 7.2% had a positive result. Whereas most ( 88,4%) of the positive samples from the ease patients showed moderate to st rong (2+ to 4+) staining in the dipstick assay, most (68.1%) of the positiv e samples from the noncase patients showed weak (1+) staining. The sensitiv ity of the dipstick assay increased from 60.1% far acute-phase serum sample s to 87.4% for convalescent-phase samples. The specificities for these two groups of samples were 94.1 and 92.7%, respectively, The dipstick assay det ected a broad variety of serogroups. The results of the dipstick assay were concordant (observed agreement, 93.2%; kappa value, 0.76) with the results of an enzyme-linked immunosorbent assay for the detection of specific IgM antibodies, a test which is often used in the laboratory diagnosis of curre nt or recent leptospirosis. This study demonstrated that this easily perfor med dipstick assay is a valuable and useful test for the quick screening fo r leptospirosis; has a wide applicability in different countries with diffe rent degrees of endemicity; can be used at all levels of the health care sy stem, including the field; and mill be useful for detecting and monitoring outbreaks of leptospirosis.