Two Test Strategy for the Diagnosis of Leptospirosis

Two Test Strategy for the Diagnosis of Leptospirosis Vaishali B Dohe*, Sae S Pol*, Alka P Karmarkar**, Renu S Bharadwaj*** Abstract Background: Leptospirosis is Spirochaetal zoonosis with protean manifestation. Rapid diagno sis is important as if appropriate therapy is instituted on time, clinical response is dramatic. The Lepto Dri-Dot test is being extensively used for rapid diagnosis especially during out breaks. Aims: To evaluate the results of Dri-Dot test with IgM ELISA and microscopic agglutination test (MAT). Material and Methods : Acute phase serum samples from 175 cases of suspected leptospirosis were screened by Dri Dot test and later confirmed by IgM ELISA test. Result: In comparison with IgM ELISA, the sensitivity and specificity of the Dri Dot was 96.46% and 72.58% respectively. Vis a Vis the MAT, the sensitivity and specificity of Dri Dot was 96.67% and 50% respectively. Conclusion: Since the specificity of Dri Dot test is low; it is useful for diagnosis of outbreaks only at the periphery where facility for ELISA are not available. In a hospital scenario, labora tory diagnosis should be done by ELISA. Introduction Leptospirosis is a Spirochaetal zoonosis of worldwide distribution.1 The disease shows protean clinical manifestations, so laboratory confirmation is a must. As isolation of leptospires from clinical samples is time consuming serology remains the mainstay of diagnosis. The ‘gold standard’ serological test is microscopic agglutination test (MAT). MAT test is very tedious and requires the maintenance of several leptospiral serovars in the laboratory. Also the test requires the expertise personnel to read the results. Therefore rapid and easy to perform tests have emerged in recent years for the diagnosis of leptospirosis. IgM ELISA is one of such test, which is popularly done for the *Lecturer; **Associate Professor; ***Professor and Head, Microbiology Department, B.J. Medical College, Pune. 18 diagnosis of acute leptospirosis. The cost of the test and requirement of specialized equipments still restricts the use of IgM ELISA in Reference laboratories only. Screening tests in the form of ‘one step’ diagnostic test, not requiring any instrumentation, emerge every year as mushrooms during the post monsoon epidemic season of leptospirosis.1-5 Majority of these rapid tests are immuno chromatographic or particle agglutination tests. Introduction of such tests in the market as diagnostic tests needs their evaluation by comparing their results with the ‘gold standard’ test, MAT and a widely used diagnostic test, IgM ELISA. The present work was done with the aim to evaluate a screening test, lepto Dri-Dot, manufactured by The Dutch Royal Tropical Institute (KIT) in Amsterdam. Also a Bombay Hospital Journal, Vol. 51, No. 1, 2009 Bombay Hospital Journal, Vol. 51, No. 1, 2009 19 diagnostic strategy for the diagnosis of leptospirosis was thought based on the results obtained in the present study. Material and Methods A total of 175 serum samples of clinically suspected leptospirosis from Pune and outside Pune were included in the study. Ten negative control sera were collected. The study was conducted at Maharashtra State Leptospirosis Diagnostic Center, B.J. Medical College Pune during January 2004 to December 2004. All sera were screened by lepto Dri-dot test. Lepto Dri-dot test is a new card agglutination test developed by the Dutch Royal Tropical Institute in Amsterdam6 for the rapid diagnosis of leptospirosis. It consists of coloured latex particles activated with a broadly reactive leptospira antigen that is dried onto an agglutination card. 10 µl serum was added to the card next to the blue dot and within area marked by the black circle. It was mixed with blue dot using flat end of spatula to get homogeneous suspension. Card was then rotated slowly in a circular motion. Results were recorded within 30 seconds after start of mixing. IgM ELISA test from Panbio, Australia was performed on all samples as per the manufacturers’ instructions. The serovar specific MAT was done on 50 sera using 10 serovars.7 The results of the Dri-dot and IgM ELISA were compared to calculate sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV). Results Results of different tests conducted on serum samples from suspected cases of Leptospirosis were shown in Tables 1 and 2. The Dri-Dot test detected 126 (72%) cases of Leptospirosis. Of this, 109 (62.28%) were positive by both Dri-Dot and IgM ELISA; while only 4 Dri-Dot negative cases were positive by IgM ELISA. Thus when the Dri-Dot was compared with IgM ELISA it gave a sensitivity of 96.46% and specificity of 72.58% (Table 3) . 50 serum samples were tested by MAT. In comparison with MAT, 39 (78%) samples were positive by Dri-Dot and 29(58%) by both; Dri Dot and MAT. So vis a vis the MAT, sensitivity and specificity of D