Accuracy of Loop-Mediated Isothermal Amplification for Diagnosis of Human Leptospirosis in Thailand

Piengchan Sonthayanon,Vanaporn Wuthiekanun,Janjira Thaipadungpanit,Thareerat Kalambaheti,Nicholas P Day,Sharon J Peacock,Wirongrong Chierakul,Lee D Smythe,Direk Limmathurotsakul,Premjit Amornchai,Siriphan Boonsilp

doi:10.4269/ajtmh.2011.10-0473

Abstract

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.

Highlights

Leptospirosis is an acute febrile illness caused by pathogenic species belonging to the genus Leptospira
We found that the rrs loopmediated isothermal amplification (LAMP) showed positive results in 58 of 133 cases and in 22 of 133 controls
Accurate laboratory diagnosis of leptospirosis is important for correct patient management, but there is a paucity of diagnostic tests that provide timely information around the time of admission

Summary

Introduction

Leptospirosis is an acute febrile illness caused by pathogenic species belonging to the genus Leptospira. Conventional and real-time polymerase chain reactions have been described for detection of pathogenic Leptospira in blood at the time of patient presentation,[2,3,4,5] and are useful for investigation of patients presenting within the first week of illness (during the leptospiremic phase of infection) in settings that have the necessary equipment and trained laboratory personnel. These assays are not in routine use in many countries where leptospirosis is highly endemic because the equipment required

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