Introduction

Leptospirosis is an emerging zoonotic disease caused by pathogenic species of Leptospira. It is transmitted to humans primarily through direct or indirect contact with the urine of infected animals or contaminated water and soil (1). Patient presents to the hospital with a broad spectrum of clinical manifestations, ranging from a mild, self-limiting febrile illness to severe, potentially fatal complications involving multiple organs (2, 3). In many endemic regions, leptospirosis still remains a leading cause of pyrexia of unknown origin (PUO) (4). Globally, it is estimated that leptospirosis accounts for approximately 1.03 million cases and 58,900 deaths annually, with the highest burden observed in tropical and subtropical countries (5). In India, the disease is particularly prevalent in the western and coastal states including Gujarat, Maharashtra, Karnataka, Tamil Nadu, and Kerala (6).

The incidence typically peaks during the monsoon and post-monsoon seasons (June to October), coinciding with heavy rainfall, flooding, and increased exposure to contaminated environments (7, 8). Pathogenic Leptospira penetrate the host through abraded skin or mucous membranes, particularly during exposure to contaminated floodwaters, moist soil, or animal reservoirs such as rodents, dogs, and cattle [9-11]. Risk factors include walking barefoot, presence of rodents in the household, occupational exposure in agriculture or sanitation, and recreational water activities (12). It is often a self-limited disease, with few cases requiring hospitalization. Although leptospirosis can often resolve without hospitalization, severe cases—particularly the icteric form, also known as Weil’s disease can lead to jaundice, renal failure, hemorrhagic manifestations, and even death (13). Identifying local environmental and behavioral risk factors is crucial for early diagnosis, community education, and implementing preventive public health strategies. In this context, the present study aims to identify environmental risk factors associated with leptospirosis among hospitalized patients in coastal Karnataka using a case-control approach

Materials and Methods

Study Design and Setting

A hospital-based case-control study was conducted to identify environmental and behavioral risk factors associated with leptospirosis. The study was approved by the Institutional Ethics Committee, and written informed consent was obtained from all participants. Data collection was conducted between June and October 2022, coinciding with the monsoon season in coastal Karnataka, India, a region with a known seasonal burden of leptospirosis.

Study Participants: Patients presenting with pyrexia of unknown origin (PUO) were screened. Blood samples received in the microbiology laboratory were tested for anti-Leptospira IgM antibodies using enzyme-linked immunosorbent assay (ELISA). Based on serology results, participants were classified as:

i) Cases (n = 42): PUO patients who tested positive for anti-Leptospira IgM antibodies and had a history of environmental exposure (e.g., contact with floodwater, livestock or pets, rodents, or contaminated soil).

ii) Controls (n = 42): PUO patients who tested negative for anti-Leptospira IgM but had a comparable history of exposure.

Inclusion Criteria: Patients were included if they presented with PUO and if they were tested for anti-Leptospira IgM by ELISA.

Exclusion Criteria: Patients were excluded if they were not tested for anti-Leptospira IgM ELISA.

Data Collection and Analysis: Data were collected through a pre-validated structured questionnaire, which captured information on demographics, occupational and environmental exposure, clinical symptoms, prior antibiotic use, and sanitation practices. Data entry and management were carried out using Epicollect5 software. Descriptive and inferential statistical analyses were performed to determine the association between exposure variables and leptospirosis.

Results

A total of 84 participants were enrolled in the study, comprising 42 cases and 42 controls. The demographic characteristics, clinical history, prior treatment, and environmental exposure data were collected using the Epicollect5 platform. There was no significant difference between cases and controls in terms of gender distribution (Figure 1). A substantial proportion of leptospirosis cases (45.2%) were outdoor unskilled workers, suggesting a potential occupational exposure risk. Most cases hailed from semi-urban (19%) and rural (14.3%) areas. As the study was conducted during the monsoon season in coastal Karnataka, nearly all participants, including controls, reported exposure to rainwater.

Figure 1: (A) Age Distribution of Cases and Controls (B) Gender distribution of cases and controls

All participants presented with fever, as per the inclusion criteria. Prior use of over-the-counter (OTC) medications before hospital presentation was reported by approximately 21–23% of both groups. Among the leptospirosis cases, high-grade fever was the most common symptom (80.95%), followed by chills (59.5%), abdominal pain (50%), vomiting (47%), and jaundice (33.3%). Notably, 95.2% of the cases had initiated antibiotic treatment prior to hospital admission, with doxycycline being the most commonly used drug, which is consistent with recommended first-line therapy for leptospirosis. The mean duration of hospital stays for confirmed cases was 7.52 days, and the majority of these patients had no previous history of leptospirosis (Table 1).

Animal exposure was reported by 69% of cases, with an estimated 4.4-fold increased risk of disease compared to controls. The most frequently reported animals included dogs, cats, and cattle. Among those exposed, 33.3% of the cases had open wounds during their contact with animals or rainwater. These wounds were most commonly located on the feet, legs, and fingers. A large proportion (95%) of cases reported wearing open footwear, increasing their risk of exposure. Furthermore, 30.95% of households of the cases lacked proper drainage, with open drains being reported in their vicinity.

Only 14.3% of cases reported travel in the two weeks preceding illness. About 47.6% of the cases gave a history of animal contact at work, and 26.2% of them had recent cuts or grazes on their limbs during exposure. A total of 80.95% of the cases reported exposure to stagnant water. Among them, 45.2% had contact with waterlogged areas, 42.9% with wet soil, 23.8% with floodwater, 11.9% with sewage water, and 7.1% with standing fresh water or public pools. Additionally, 35.7% of cases reported the presence of open sewage around their homes.

Although the majority of both cases and controls consumed treated water, nearly 50% relied on well water, a common source of drinking water in the coastal Karnataka region. The use of indoor latrines was reported by 97.6% of participants, with outdoor defecation being rare. Public toilet usage was reported by 14.3%, and 7.1% of patients used other shared facilities. Importantly, none of the cases reported wearing protective clothing, and 95% admitted to not wearing protective footwear while at work, underscoring significant gaps in personal protective practices (Table 2).

Discussion

In India the west coastal states of Gujarat, Maharashtra, Goa, Karnataka and Kerala are affected by leptospirosis. The positivity rate for the disease is notable in the southern part of India at 25.6%, followed by 8.3%, 3.5%, 3.1%, and 3.3% in northern, western, eastern and central India, respectively (14). Agricultural activities, contact with farm animals, exposure to sewage water are most common modes of exposures for acquiring leptospirosis in India (15). There is no gender difference seen among cases verses controls in our study. Majority (45.2%) cases were outdoor unskilled workers. Heavy rain falls, improper drainage system, outdoor activities which exposed them to mud, stagnant water and animals(P=0.001), not wearing footwear or wearing open foot wear were significantly associated with leptospirosis cases in our study which is concordant with other studies conducted in India (16, 17). Exposure to waterlogged areas is seen in 45.23% of cases which is significantly higher in infected cases. These waterlogged areas act like reservoirs where the Leptospira multiply and present in high number.

History of direct exposure to rodents is less in our study compared to other animals like cattle, dogs, cats which is contrast to other studies conducted in India (17, 18). But in any farming activity, there will be wastages which will attract the rodents resulting in mixing of rodent urine in the soil and water. Patients can get exposed to such soil or water with Leptospira unknowingly and get the disease. There was a history of cut in the skin in 33.3% cases compared to 19.04% of controls (Figure 2). A study by Udayar et al. found significant association between skin wounds and leptospirosis infection (17). 95% patients gave the history of not wearing protective clothing or footwear while doing outdoor activities. These practices along with non-intact skin will make them prone for acquiring the disease.

Figure 2: Graphical abstract on good and bad practices in leptospirosis along with percentage predisposition to disease due to the features

In developed countries, the disease is most often recognized in people with occupational activities that involve water exposure or interactions with animal reservoir hosts or in people participating in recreational activities involving water. Wildlife trapping for research purposes, production animal work (abattoir work, dairy farming, veterinarians working with livestock), water-intensive crop farming (bananas, pineapples, taro, rice, berries), military operations, fish farming, and sewer work increase risk for leptospirosis (18, 19).

In India the majority of leptospirosis cases are found in the western and coastal states. Most of the patients (74.7%) recover without any complications and nearly one-fifth of them recovered with complications (21.8%). Acute renal failure was the most commonly seen (79.2%) complications. The case fatality was found to be 3.5%. There was a significant increase in the mortality documented from the state of Kerala when the infected patients have other comorbid conditions or when they have infection due to other hemorrhagic viruses. As the environmental factors responsible for Leptospirosis and hemorrhagic fevers like dengue are similar, there was significant co-infection found to as high as 17.5% from southern part of India (20).

Our study shows the importance of basic behavioral changes required for the prevention of Leptospira infection and its complications. Measures like protective clothing, footwear, gloves while working in paddy field and farms to avoid direct contact with the contaminated soil or stagnant water are essential to avoid any infection. There is a need of awareness in the people and health education should be given regarding disease and its risk factors.

Conclusion

This study underscores the significant association between environmental exposures and the occurrence of leptospirosis among hospitalized patients in coastal Karnataka. Factors such as direct or indirect contact with animals, exposure to stagnant or contaminated water, lack of protective footwear and clothing, and presence of open wounds were strongly associated with increased risk of infection. The findings highlight the need for targeted public health measures, including community awareness, personal protective practices, and improved sanitation infrastructure, particularly during the monsoon season. Identifying and addressing these risk factors is essential for early diagnosis, prevention, and reduction in disease burden in endemic regions.

Conflict of Interest: Authors declare no conflict of interest

Acknowledgement: We would like to thank the technical staff at the department of Microbiology for helping in performing IgM ELISA

Funding: No funding was received for this study

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