We show that a large proportion (21%) of febrile patients presenting to a Nepali hospital/clinics during summer season had serologic evidence of acute leptospirosis. A study conducted at Chitwan Medical College across 1266 patients suspected of leptospirosis revealed sero-positivity in 61 (4.8%) cases . When restricted to analysis of patients presenting during the summer, their sero-positivity rate was 21.3%, which is in line with our findings.
Most of the sero-positive cases were within the 21–30 and 31–40 age groups. The clustering of the disease in these age groups is consistent with occupational exposures in these “working” ages. In the study carried out by Seti et al.,  most of the patients (70%) positive for leptospirosis were young adults in their 2nd, 3rd or 4th decades of life. Similarly, in another study done by Chawla et al. , the highest percentage of positive for leptospirosis cases were from the middle age group. We found a higher incidence of leptospirosis among females that was not statistically significant, in contrast with previous studies demonstrating higher incidence of leptospirosis in males [23,24,25,26]. The higher incidence in females at our site may be due to emigration of males to foreign countries for work, resulting in an increase in female participation in farming and other work previously dominated by males.
Of the cases having animal contact (cattle, buffaloes and pets), 26.6% were seropositive. Rearing cows and/or buffaloes is a common practice in Nepal, and these animals are often chronically colonized by pathogenic Leptospira with frequent transmission to humans . The Directorate of Animal Health, Nepal reported an overall 10.5% incidence of leptospirosis in cattle and buffalo, goat, sheep and pig. Dogs have become popular pets with a risk of Leptospira transmission . In a study conducted in 150 dogs presenting with fever and jaundice, serological positivity for leptospirosis was established in 2.7% (4/150) of those . Similarly, of the cases having water contact, 41.8% were ELISA positive. The study period coincides with the paddy growing season in Nepal, and an increase in leptospirosis has been associated with the rice paddy harvesting season where an increase in the rodent population in and around the field is observed . Swimming in pools or white water rafting as a recreational activity is becoming popular in urban areas of Nepal too. Numerous studies have shown that such activities have been associated with leptospirosis [30, 31].
Leptospirosis has traditionally been considered a disease of farmers [29, 30]. In accordance to these findings, the present study also revealed to be most common among farmers, followed by students, masons, housewives, servicemen and businessmen. Their profession didn’t carry any risk for leptospirosis and seems like they might have acquired it by accidental animal/water contact.
One of the patients who tested sero-positive for leptospirosis also tested positive for Widal test. Clinical manifestations did not hint at the worsening of clinical symptoms of the patient, as expected for the co-infections. Blood samples from the patient in the first week of fever was not available for culture to trace the microbial etiology of the Widal positivity (convalescence samples were also not available). Since this test is non-specific, positive results may also indicate the cross reactivity with antibodies specific to bacterial (members of enterobacteriaceae) and non-bacterial (malaria, dengue, hepatitis A, and infectious mononucleosis) diseases and may have previous infection .
1/144 samples also showed seropositivity for both leptospirosis and dengue specific IgM. The positive IgM result for dengue could be considered an old infection. The IgM antibodies for dengue generally remain in circulation for prolonged periods of time. Clinical presentation of dengue fever and leptospirosis are considerably overlapping, leading to misdiagnosis in cases of mixed infection. In acute stage of infection, both present as acute febrile illness with chills, myalgia, headache, abdominal pain, and anorexia. Though dengue IgM can persist for months, the severity of the observed symptoms in the patient suggested that it could more likely be a simultaneous infection of dengue and leptospira. This patient also presented arthalgia in addition to non-specific symptoms of leptospirosis, inferring the symptomatic aggravation by the co-infection. Such co-infections have been previously reported in Nepal and India [33, 34].
This study has several limitations, the greatest of which is its cross-sectional nature, as we were not able to collected paired serum samples. Secondly, we only collected samples over a short duration, though we chose the summer season as it has the highest incidence of disease. Thirdly, MAT, the gold standard test for leptospirosis could not be done, nor we could perform blood culture or any molecular tests. However, we believe that the result of this study describes the general features of the disease in Nepal.