Laboratory diagnostic, epidemiological, and clinical characteristics of human leptospirosis in Okinawa Prefecture, Japan, 2003-2020

Abstract

Background: Leptospirosis is considered an endemic disease among agricultural workers in Okinawa Prefecture, which is the southernmost part of Japan and has a subtropical climate, but data on the current status and trend of this disease are scarce.

Methodology/principal findings: We conducted a retrospective study of clinically suspected leptospirosis patients whose sample and information were sent to the Okinawa Prefectural Institute of Health and Environment from November 2003 to December 2020. Laboratory diagnosis was established using culture, nested polymerase chain reaction (PCR), and/or microscopic agglutination test (MAT) with blood, cerebrospinal fluid, and/or urine samples. Statistical analyses were performed to compare the epidemiological information, clinical features, and sensitivities of diagnostic methods among laboratory-confirmed cases. Serogroups and the species of Leptospira isolates were determined by MAT using 13 antisera and flaB sequencing. A total of 531 clinically suspected patients were recruited, among whom 246 (46.3%) were laboratory confirmed to have leptospirosis. Among the confirmed cases, patients aged 20-29 years (22.4%) and male patients (85.7%) were the most common. The most common estimated sources of infection were recreation (44.5%) and labor (27.8%) in rivers. Approximately half of the isolates were of the L. interrogans serogroup Hebdomadis. The main clinical symptoms were fever (97.1%), myalgia (56.3%), and conjunctival hyperemia (52.2%). Headache occurred significantly more often in patients with Hebdomadis serogroup infections than those with other serogroup infections. The sensitivities of culture and PCR exceeded 65% during the first 6 days, while the sensitivity of MAT surpassed that of culture and PCR in the second week after onset. PCR using blood samples was a preferable method for the early diagnosis of leptospirosis.

Conclusions/significance: The results of this study will support clinicians in the diagnosis and treatment of undifferentiated febrile patients in Okinawa Prefecture as well as patients returning from Okinawa Prefecture.

Fig 1. Sample collection and the results for laboratory diagnostics.

The lowest boxes indicate the results of laboratory diagnostics, culture, DNA detection by flaB-nested PCR, and antibody detection by microscopic agglutination test (MAT). The numbers in the lowest boxes represent the number of positives / the number of patients tested. +; successful collection, -; unsuccessful collection, CSF; cerebrospinal fluid.

Fig 2. Comparisons of the sensitivity of diagnostic methods on day of illness among laboratory-confirmed cases (N = 238).

Each plot indicates the number of positives / the number of samples tested. The reciprocal MAT titer 320 was regarded as positive, irrespective of acute or convalescent samples in this figure. Seven cases were not included in this analysis because of lack of information. The PCR-positive case on day 14 was a patient with diabetes. The vertical bars indicate the 95% confidence intervals.

Fig 3. Distributions of PCR-positivity among blood, cerebrospinal fluid (CSF), and urine (N = 125).

The PCR-positive results in blood and urine samples on day 14 were detected from a single patient with diabetes.

Fig 4. Distributions of the results of flaB-nested PCR in blood and urine samples from single patients (N = 96).

The PCR-positive case on day 14 was a patient with diabetes.