Relevance of Polymerase Chain Reaction in Early Diagnosis of Leptospirosis

Aim and background: Leptospirosis is common in India, especially in the southern states. Mortality is high among untreated cases. Diagnosis of leptospirosis remains a challenge in India as polymerase chain reaction (PCR), which is more sensitive than Immunoglobulin M (IgM) is not widely available. This study aimed to find out the difference in diagnostic yield with PCR and IgM in early leptospirosis. Materials and methods: This retrospective, single-center study included 67 adults with laboratory-confirmed leptospirosis (IgM, PCR, or both) who presented within 7 days of symptom onset and were admitted to the intensive care unit (ICU). The difference in the diagnostic yield with PCR and IgM ELISA was studied. Results: About 77.6% of the patients tested positive by PCR and 55.2% tested positive by IgM. There was a statistically significant difference in the detection of leptospirosis by PCR and IgM (p-value = 0.036). In the subgroup of patients who presented within 3 days of onset of symptoms, PCR positivity was 90.32% whereas IgM positivity was only 25.8%. Conclusion: Our study showed that the sensitivity of leptospira PCR is significantly higher than IgM in the first week of illness. It also showed that among the subset of patients who died, a majority were detected only by PCR. Since PCR is not widely available, leptospirosis remains underdiagnosed and mortality from the same is underestimated. Polymerase chain reaction, if routinely done along with IgM for all suspected cases of leptospirosis that present within the first week of illness helps in prompt diagnosis and treatment.