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Task Force study on disease burden due to leptospirosis in India

The phase I of the ICMR task force study on disease burden due to leptospirosis was conducted with the objective of assessing the role of leptospirosis in causing acute febrile illness in different parts of the country and to generate data on the clinical spectrum, infecting serogroups and the risk factors of leptospirosis. Twelve centres from different parts of the country participated in the study. The participating centres are listed in table below (table 1).

  S. No Centre/hospital City / Town State  
1 Regional Medical Research Centre Bhubaneswar Orissa
  2 Sher-i-Kashmir Institute of Medical Sciences Srinagar Jammu & Kashmir  
3 Desert Medicine Research Institute Jodhpur Rajasthan
4 Kasturba Medical College Manipal Karnataka
5 All India Institute of Hygiene and Public Health Kolkata West Bengal
6 Regional Medical Research Centre Dibrugarh Assam
  7 Malankara Orthodox Syrian Church Mission Hospital Kolenchery Kerala  
8 Mahatma Gandhi Institute of Medical Sciences Wardha Maharastra
9 Sanjay Gandhi Institute of Medical Sciences Lucknow Uttar Pradesh
10 PG Institute of Medical Education & Research Chandigarh Chandigarh
11 BJ Medical College Pune Maharastra
12 Nizam’s Institute of Medical Sciences Hyderabad Andhra Pradesh

Table 1. Partcipating Centres in the Phase I ICMR Task Force Study on disease burden due to leptospirosis in India

A total of 3609 patients were screened during a period of one year. Out of them, 532 (14.7%) were diagnosed to have leptospirosis based on dipstick results. Microscopic agglutination test was done on 951 patients. Paired samples were available for only 670 patients. Based on seroconversion, four-fold rise in titre or a minimum titre of 1:160 in either of the samples, a diagnosis of leptospirosis was confirmed in 264 patients. Diagnosis in 200 patients was based on paired MAT and in the remaining 64 it was based on a minimum titre of 1:160 in a single sample. Based on MAT titres, the commonest serogroup was Autumnalis followed by Icterohaemorrhagiae, Grippotyphosa and Australis.

 Fig 1. Serogroup distribution based on MAT titres (ICMR Task Force Study on disease burden due to leptospirosis in India)
 

Fig 2. Relationship between dipstick positivity rate

and MAT titres

The widest distribution was for serogroup Icterohaemorrhagiae followed by Autumnalis. Distribution of different serogroups is summarized in fig. 1

Dipstick positivity rates among samples with different MAT titres showed a logarithmic trend (Fig 2). The sensitivity of dipstick test done at the participating centres in comparison with paired MAT was 97.7% (when compared patient to patient) and specificity was 71%. The overall concordance between dipstick and MAT was 71%.

 
   

Fig 3. Relationship between dipstick positivity rate and MAT titres

 

Dipstick positivity rates among samples with different MAT titres showed a logarithmic trend (Fig 1.81). The sensitivity of dipstick test done at the participating centres in comparison with paired MAT was 97.7% (when compared patient to patient) and specificity was 71%. The overall concordance between dipstick and MAT was 71%.

 

 

Month-wise patient recruitment, dipstick and MAT results are summarized in Fig. 3 There is a peak during June – July months, however since the number of patients to be recruited per month was fixed before the study, the variation in the number of patients recruited from month to month may not be an actual reflection of the seasonal trend in the incidence. At the same time, it is possible that non-availability of sufficient number of patients fulfilling the clinical diagnostic criteria was a reason for the lower number of patients recruited during the other months.

Prevalence of symptoms/signs among MAT positive and negative patients were compared and the rate ratios were calculated. Hematuria was the symptom with the highest rate ratio (3.69). Ten symptoms had rate ratios significantly higher than 1.0. Multiple logistic regression done with presence of leptospirosis as the dependant variable and various symptoms/signs as independent variables showed that headache, diarrhoea, haematuria and oliguria are independent predictors of leptospirosis. The model could correctly predict 70.7% of the results (85.0% in the case of negative results and 52.7% in the case of positive results).

 

Symptom/sign

b

OR

95% CI

p

  
 

Headache

1.26

3.53

(2.33, 5.76)

< 0.001

  
 

Diarrhoea

0.93

2.53

(1.58, 4.06)

< 0.001

  
 

Haematuria

1.00

2.72

(1.53, 4.85)

0.001

  
 

Oliguria

0.96

2.61

(1.75, 3.91)

< 0.001

  
 

Constant

-1.10

0.33

  

< 0.001

  
             
 

Table 2. Table Independent predictors of leptospirosis

  
     

A comparison of mean values of various biochemical and hematological values among dipstick positive and negative patients was made. A similar comparison could not be made between MAT confirmed patients and negatives because of the small number of observations available. Serum sodium and bicarbonate concentration were the only biochemical parameters whose mean value differed statistically significantly among dipstick positive and negative patients. A comparison was also made on the prevalence of various biochemical and hematological abnormalities among dipstick positive and negative patients. Prevalence of four parameters were statistically significantly different among the two groups (Table 1.19). These were leucocyte count above 10,000/mm3(less common among dipstick positives), serum sodium concentration less than 135 mmol/L (more prevalent among dipstick positives), platelet count less than 150,000/ mm3(more prevalent among dipstick positives) and leucocyte count less than 4,500/ mm3 (less prevalent among dipstick positives). The difference in the prevalence of elevated serum creatinine level and low blood glucose levels were only marginally significant. Hyperkalemia had the highest rate ratio, but the difference in the prevalence was statistically not significant.

 
   Factor b OR

95.0% C.I.

 Sig.  
  Rivers nearby 0.85 2.34 1.58 - 3.49 0.000  
Drinks well water 0.82 2.28 1.53 - 3.40 0.000
Baths in ponds 0.52 1.68 1.09 - 2.59 0.020
Works in farms 0.50 1.65 1.13 - 2.39 0.009
Constant -1.57 0.21 0.000

Table 3. Risk factors of leptospirosis—results of multiple logistic regression (ICMR Task Force study on disease burden due to leptospirosis in India)

A univariate analysis showed that several socio-economic, environmental, behavioural and occupational factors had significant association with leptospirosis. Multiple logistic regression identified four factors were found to be independent risk factors of leptospirosis (diagnosed based on MAT results) (Table 1.20). These were presence of rivers near the house, use of well water for drinking purpose, bathing in ponds and working in farms.

The number of patients screened was less than half of the set sample size. There was a wide variation in the number of patients included in different centres. Although the original plan was to use MAT results on paired samples as the criteria for diagnosis, paired samples were not available for all the patients and hence in a large number of patients, the diagnosis had to be made on the basis of dipstick results. Three centres in the west cost i.e. Kolenchery in Kerala, Manipal in Karnataka and Pune in Maharashtra contributed 46% of the patients included in the study and 73% of the patients diagnosed to have leptospirosis. These areas are comparatively more endemic for leptospirosis and hence the overall positivity rate observed could be an over-estimation.

In spite of these limitations, the study could generate some baseline information about the presence of leptospirosis in different parts of the country. Because of the disproportionately high representation of three centres in the west cost the observed positivity rate could be an over-estimation. In spite of this the study shows that leptospirosis is not a rare occurrence in most parts of India.