Urine PCR testing as an effective method for early diagnosis of leptospirosis

Abstract

The role of urine PCR for leptospirosis diagnosis in the first week is controversial due to assumed limited urine excretion. This study analyzed the prescribing practices and sensitivity of blood and urine Leptospira PCR, particularly in early stages of infection. A study was conducted on adult patients diagnosed with leptospirosis in French Guiana between 2016 and 2022 by positive Leptospira PCR, or titer of Micro-Agglutination Test > 1/200, or positive IgM with no alternative diagnosis. The timing of PCR tests and their sensitivity were analyzed. A multivariate logistic regression was performed to identify the factors associated with the sensitivity and predict the probability of having a positive result. Among 188 analyzed patients, 137 (73%) and 61 (32%) underwent blood and urine PCR tests with a median (IQR) delay since symptoms onset of 5 (3-7) and 6 (5-8) days, respectively. The overall sensitivity of urine PCR was 84% (vs 70% for blood PCR, P = 0.04). Of the 25 patients sampled the same day in the first week, eight had negative blood PCR but positive urine PCR. Contrary to urine, the sensitivity of blood PCR significantly decreased with time since symptom onset (aOR 0.56 per day, 95% CI [0.44-0.73]). The predicted probability of positive urine PCR appeared higher than that of blood PCR as soon as 4 days after symptom onset. Urine PCR should be considered at the first consultation, alongside blood PCR.

Importance: The study investigates the utility of urinary PCR for diagnosing leptospirosis, focusing on its early sensitivity. Conducted in French Guiana between 2016 and 2022, the research analyzed prescribing practices and the sensitivity of blood and urine PCR tests in adult patients. Results indicated that while underutilized, urinary PCR demonstrated high sensitivity from the early days of symptom onset, achieving 84% sensitivity compared to 70% for blood PCR. The sensitivity of blood PCR decreased over time, whereas that of urinary PCR remained stable. The study advocates for the routine inclusion of urinary PCR in the diagnostic workup from the first week of illness to enhance early leptospirosis detection.

Keywords: PCR; diagnosis; leptospirosis; urine.

Fig 1

Flow chart of distribution and results of blood and urine PCR tests in the study patients.

Fig 2

Sensitivity of blood and urine PCR (left axis) and number of tests (right axis) according to the delay between symptom onset and sampling. (A) Blood PCR. * One patient had a blood sample collected 17 days after symptom onset. (B) Urine PCR. * One patient had a urine sample collected 26 days after symptom onset.

Fig 3

Correlation between the sensitivity of PCR testing and delay between symptom onset and sampling during the first 14 days of illness. (A) Blood PCR. (B) Urine PCR.

Fig 4

Predicted probabilities of positive PCR based on the logistic regression multivariable models for blood PCR and urine PCR. (A) Blood PCR. (B) Urine PCR.