Case fatality rate of leptospirosis in a tertiary care hospital in Kerala, India


Context: Leptospirosis is under-reported because of its wide spectrum of signs and symptoms. The infection mainly occurs in farmers and individuals involved in water-related jobs and activities and it can be 100 times more frequent in tropical areas. Aim : The present hospital-based study was conducted in an endemic area of tropical country to find out the case fatality of this disease over time, age, and sex. Settings and Design : It was a hospital-based retrospective study of five years conducted in a tertiary care hospital in Kerala, India. Materials and Methods : The data were collected from registers maintained in the medical records department and analysed by using Microsoft excel. Statistical Analysis : Chi-square and ‘Z’ tests were applied for the comparison of proportions. Results : Of the 1,523 confirmed cases, 993 (65.20%) were male and 530 (33.02%) were female. Of the confirmed cases, 63 died: 44 (69.84%) male and 19 (30.15%) female. The case fatality of leptospirosis was 4.13%, and it was high in the age group 40-60 years in both sexes. Of the 63 deaths, 20 (31.74%) were due to multiple organ dysfunction and 12 (19.04%) due to renal failure. The case fatality rate was high in males and it increased with age in both sexes. The case fatality rate of leptospirosis varied in the age groups <20 and ≥60 years, which were 1.22% and 19.32%, respectively. The case fatality of males was 4.43% and of females it was 3.58%. Conclusion : It was suggested that effective leptospirosis control in endemic areas needs a multifactorial approach.

Keywords: Age, case fatality rate, sex

How to cite this article:
Antony J, Celine T M, Chacko M. Case fatality rate of leptospirosis in a tertiary care hospital in Kerala, India. Ann Trop Med Public Health 2012;5:236-9
How to cite this URL:
Antony J, Celine T M, Chacko M. Case fatality rate of leptospirosis in a tertiary care hospital in Kerala, India. Ann Trop Med Public Health [serial online] 2012 [cited 2020 Aug 5];5:236-9. Available from:

Leptospirosis is reported from all parts of the world, especially from the tropical and sub-tropical areas. It is caused by a pathogenic spirochete of genus Leptospira and acquired through contact with certain animal reservoirs or an environment contaminated by urine and feces of such animals. [1] The infection is underestimated and underdiagnosed [2] even in endemic areas because of its broad spectrum of signs and symptoms, which vary from a self-limited febrile illness, to severe, life-threatening diseases such as Weil’s disease with multiple organ failure. The present hospital-based study focused on the case fatality of leptospirosis in an endemic area over a five-year period as well as its age and sex distribution.

Materials and Methods

This retrospective study was restricted to 1,523 patients of confirmed leptospirosis admitted to a tertiary care hospital in Kerala, India, from January 2005 to December 2009. The data were retrieved from medical records department of the hospital. The patients under study were divided into different age groups of 20-year interval such as 0-20, 20-40, 40-60, and >60 above for the analysis. The data were processed and statistically analyzed by using Microsoft excel. ‘Z’ and Chi-square tests were applied for comparison of proportions.


A total of 1,523 confirmed patients were admitted to the hospital during the study period of five years from January 2005 to December 2009. Of these, 993 (65.20%) were male and 530 (33.02%) were female. The proportion of male cases was higher than female cases. The number of cases increase with age and this increase steadily goes up to 60 years. The number of cases in the age group <20 and ≥20 years was 16.02% and 83.97%, respectively. In males, 170 (17.1%) cases were <20 years and 823 cases (82.88%) were ≥20 years. In females, 74 (13.96%) cases were <20 years and 456 (86.03%) were ≥20 years of age. [Table 1] shows the further age and sex wise distribution of leptospirosis cases.

Table 1: Age and sex-wise distribution of cases and deaths

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Of the confirmed cases, 63 patients died. Of these, 44 (69.84%) were male and 19 (30.15%) were female. Of these 63 deaths, 20 (31.74%) were due to multiple organ dysfunctions and 12 (19.04%) due to renal failure. The case fatality of leptospirosis during the study period was 4.13%; in males, it was 4.43% and in females it was 3.58%. The case fatality rate of leptospirosis also increased steadily with age. It varied from 1.22% for the <20 years to 19.32% for those aged ≥60 years. The fluctuations in cases and case fatality over the years are depicted in [Figure 1] and [Figure 2], respectively. The sex-wise trend of case fatality over the years is depicted in [Figure 3].

Figure 1: Leptospirosis cases from 2005 to 2009

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Figure 2: Case Fatality of leptospirosis

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Figure 3: Sex wise case fatality

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The study reports about the infection in almost all countries, developing as well as industrialized countries such as Japan [3] , Korea [4] , Kenya [5] , Srilanka [6] , Thailand [7] , Vietnam [8] , Australia [9] , and Italy [10] . In most countries, the infection is endemic. In India, outbreaks of leptospirosis have been reported from almost all states such as Kerala [11] , Tamil Nadu [12] , Karnataka [13] , Orissa [13] , Gujarat [14] , Uttar Pradesh [13] , Maharashtra, [15] as well as Andaman and Nicobar Islands. [13]

The study area is endemic for the infection. In the present study, the case fatality was 4.13% and this is higher than that reported in Thailand (1.4%) [7] , Sri Lanka (9%) [6] , Madras (5%) [11] ; this less than that in Kerala (5.32%) [12] (where the study was conducted in 1997), Calicut (6.03%) [16] , Orissa (7.69%) [13] , Seychelles (8%) [17] , Mumbai (11.1%) [15] , Japan and Philippines (12.4%) [3] . The value is less than from Barbados (12.7%) [18] , Gujarat (18.4%) [14] , and Italy (22.6%). [11]

In the present study, an increase in case infection with age was observed. About 16.02% of the cases were below the age of 20 years and 83.97% were ≥20 years. The cases increased with age and this continued up to 60 years. In both sexes, a high percentage of cases was seen in the age group of 40-60 years. Similar observation has been reported in many studies. Everard et al.[18] in their study reported that the incidence of infection in both males and females increases with age, and this increase goes up to 60 years. Laras et al.[19] in their study on the importance of leptospirosis in Southeast Asia revealed an increase in prevalence rate with age. The study report of Regional Medical Research Centre on Prevalence and Incidence among population groups, Andaman Islands [20] , also observed the same trend, indicating a higher probability of occupational exposure being responsible for this increase. A similar pattern was observed in case fatality. As consistently reported in other studies among hospitalized patients with leptospirosis, the present study also reports the increase in case fatality with age and it is highly significant (P<0.001). Antonio Lopes et al[21] in their comparative study of the in-hospital case fatality rate of leptospirosis between pediatric and adult patients of different age groups state that the case fatality of leptospirosis was significantly lower for the pediatric group (<19) than for the adult group (>19); further, in adults, the case fatality rate of leptospirosis increased steadily from younger to older groups.

The present study showed the preponderance of males in the cases and case fatality of leptospirosis. Here, 64.32% of infection was in males and 35.67% in females. The case fatality was higher in males (4.51%) than in females (3.58%) but not statistically significant. The predominance of males in disease or case fatality highlights the probability of occupational component in disease transmission. Several other studies also revealed the same observation in case infection. A study on human leptospirosis in Ethiopia by Yimer et al. have shown the preponderance of males than females. [22] Panaphut et al. in their study of prognostic factors for death in leptospirosis found a high percentage of male cases (94.2%). [23] Everard et al.[18] showed in their study of prevalence of severe leptospirosis in humans on Barbados islands and also stated more cases in males (68%). In their study, Claude et al[24] found a high predominance of males in case infection. While Tangkanakul et al[7] revealed a decreasing male:female ratio of leptospirosis infection in Thailand (from a high of 9:1 in 1995 to 3:1 in 2003), stressing that the male population is more affected than female population. Lopes et al. showed a preponderance of males in their comparative study of the in-hospital case fatality rate of leptospirosis between pediatric and adult patients in different age groups.

A similar observation was described by Ko et al. in their study on urban epidemic of severe leptospirosis in Brazil. [25] However, this pattern was not confirmed in all studies conducted in neighboring countries. There is no difference in the male:female prevalence found in studies conducted in the Mekong Region in Vietnam [8] and South East Asia [19] where exposure may be more related to frequent flooding. Studies show that wherever male preponderance is reported high, there is also a greater involvement of males as compared to females in the outdoor works, and hence have a higher probability of contact of contaminated environment and infected animals. Many studies have shown that the exposure of humans to water contaminated with urea is the major medium of disease infection. Indian studies are reported from all parts of the country and most of these are from along the coastlines of Gujarat [16] , Mumbai [26] , Kerala [26] , Chennai, [26] and Andaman Islands. [26] A retrospective analysis of children during 1989-1995 in Sao Paulo, Brazil, has shown that the source of infection in 88% of the cases was exposure to contaminated water during floods. [27] An urban epidemic of leptospirosis in 193 adults was recently reported in the slum of Salvador, Brazil, which had a history of exposure with flood water contaminated by rat urine. [25] The study area also had a high probability of contact with contaminated water not mainly because of flooding, but also due to exposure to contaminated water during their outdoor work in paddy fields, rubber, or pineapple crops. In the study area, males were mainly involved in the cultivation of rubber crops and pineapple, animal rearing, as well as agricultural labor. Therefore, they are more susceptible to such infections as they are in continuous contact with contaminated water. This water can easily penetrate the delicate skin surface or other mucus membrane or through wounds on limbs cause by harsh leaves of pineapple or knife or other sharp tools during cultivation of crops; moreover, the wounded surface of the body may come in direct contact with infected urine or water contaminated with the urine of rodents or other infected animals. Prolonged exposure of the skin to contaminated water provides an opportunity for leptospira to invade the skin, thus causing leptospirosis. [28]

While in urban areas, domestic rats and stray dogs are known to be predominant sources of the pathogenic leptospira, [29] the rural areas of tropical countries by nature itself ensure that a high possibility of animal settlement and unhealthy human practices also promote its multiplication, especially the rodents. Definitely, in endemic areas, they might have become infected with the causative agent and contaminate the environment, mainly the water collections, and these factors make the study area a leptospirosis-prone area. Since people in rural areas work in the field without any specific and essential preventive measures and are in continuous contact with contaminated water, there is a high probability of acquiring the infection.


Even though nature is the known factor for the endemicity of this disease, man plays a vital role in contamination of environment due to careless management of food waste and other unhealthy practices, which promote multiplication of animals, thus creating a contaminated environment, especially water collections. Therefore, an effective leptospirosis control, especially in endemic areas, needs a multifactorial approach including major behavioral change through awareness and action programmes.

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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1755-6783.98626


[Figure 1][Figure 2], [Figure 3]


[Table 1]

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