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

Tetsuya Kakita,Hisako Kyan,Masato Miyahira,Emi Kitashoji,Katsuya Taira,Nobuo Koizumi,Sho Okano,Vasantha Kumari Neela

doi:10.1371/journal.pntd.0009993

Abstract

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. 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. 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.

Highlights

Leptospirosis is the most common zoonotic disease and is caused by infection with pathogenic spirochetes of the genus Leptospira, which comprises 64 species divided into 24 serogroups and more than 300 serovars [1–4]
Okinawa Prefecture is located in the southernmost part of Japan, has a subtropical climate, and is a major tourist destination, with an estimated 10 million visitors annually
Leptospirosis was considered an endemic disease among agricultural workers; during the last 17 years, most of the confirmed cases in Okinawa Prefecture were attributable to recreation or labor in rivers in the summer in the northern part of the main island of Okinawa and the Yaeyama region, which are designated as national parks with abundant nature

Summary

Introduction

Leptospirosis is the most common zoonotic disease and is caused by infection with pathogenic spirochetes of the genus Leptospira, which comprises 64 species divided into 24 serogroups and more than 300 serovars [1–4]. One million cases of human leptospirosis occur worldwide annually, along with 58,900 deaths [8]. Seventy-three percent of the world’s leptospirosis cases and deaths occur in tropical regions [8]. Human leptospirosis is characterized by a range of clinical symptoms, ranging from mild influenza-like illnesses (such as fever, myalgia, and headache) to a severe form called Weil’s disease (which presents with jaundice and acute renal failure) and leptospirosis pulmonary hemorrhage syndrome (which presents as pulmonary hemorrhage without jaundice or renal failure). The mortality rates of Weil’s disease and leptospirosis pulmonary hemorrhage syndrome are >10% and >50%, respectively [9]. Since most symptomatic patients present with a mild form of the disease, with nonspecific manifestations that are confused with those of other infectious diseases in the tropics, such as dengue fever, malaria, and scrub typhus, leptospirosis remains a significant diagnostic challenge for clinicians [6,10]. 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

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Conclusion