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There is a lack of diagnostic tests for leptospirosis in technology-restricted settings. We developed loop-mediated isothermal amplification (LAMP) specific for the 16S ribosomal RNA gene (rrs) of pathogenic and intermediate group Leptospira species. The lower limit of detection was 10 genomic equivalents/reaction, and analytical specificity was high; we observed positive reactions for pathogenic/intermediate groups and negative reactions for non-pathogenic Leptospira species and other bacterial species. We evaluated this assay in Thailand by using a case–control study of 133 patients with laboratory-proven leptospirosis and 133 patients with other febrile illnesses. Using admission blood, we found that the rrs LAMP showed positive results in 58 of 133 cases (diagnostic sensitivity = 43.6, 95% confidence interval [CI] = 35.0–52.5) and in 22 of 133 controls (diagnostic specificity = 83.5, 95% CI = 76.0–89.3). Sensitivity was high for 39 patients who were culture positive for Leptospira spp. (84.6, 95% CI = 69.5–94.1). The rrs LAMP can provide an admission diagnosis in approximately half of patients with leptospirosis, but its clinical utility is reduced by a lower specificity.
Financial support: This study was supported by the Thailand Research Fund and the Wellcome Trust.
Authors' addresses: Piengchan Sonthayanon, Department of Molecular Tropical Medicine and Genetics, Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand, E-mail: email@example.com. Wirongrong Chierakul, Department of Clinical Tropical Medicine, and Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand, E-mail: firstname.lastname@example.org. Vanaporn Wuthiekanun, Janjira Thaipadungpanit, Siriphan Boonsilp, and Premjit Amornchai, Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand, E-mails: email@example.com, firstname.lastname@example.org, email@example.com, and firstname.lastname@example.org. Thareerat Kalambaheti, Department of Microbiology and Immunology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand, E-mail: email@example.com. Lee D. Smythe, World Health Organization/Food and Agriculture Organization of the United Nations/World Organisation for Animal Health Collaborating Centre for Reference and Research on Leptospirosis, Western Pacific Region, Communicable Disease Unit, Queensland Health Forensic and Scientific Services, Brisbane, Queensland, Australia, E-mail: Lee_Smythe@health.gld.gov.au. Direk Limmathurotsakul, Department of Tropical Hygiene and Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand, E-mail: firstname.lastname@example.org. Nicholas P. Day, Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand and Center for Clinical Vaccinology and Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, United Kingdom, E-mail: email@example.com. Sharon J. Peacock, Department of Microbiology and Immunology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand and Department of Medicine, University of Cambridge, Addenbrooke's Hospital, Cambridge, United Kingdom, E-mail: firstname.lastname@example.org.
Reprint requests: Piengchan Sonthayanon, Department of Molecular Tropical Medicine and Genetics and Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, 420/6 Rajvithi Road, Bangkok, 10400, Thailand, E-mail: email@example.com.