ANNUAL RISK OF TUBERCULOUS INFECTION IN RURAL AREAS OF KOTA DISTRICT*

Transcription

1 Original Article ANNUAL RISK OF TUBERCULOUS INFECTION IN RURAL AREAS OF KOTA DISTRICT* Preetish Vaidyanathan 1, V.K. Chadha 2, P. Kumar 3, P.S. Jaganatha 4 and G. Uma Devi 5 Summary: Background: A nation wide tuberculin study was undertaken to estimate the Annual Risk of Tuberculous Infection (ARTI) in different parts of India. The study in the rural areas of Kota, one of the districts selected for the survey, is described in this article. Material & Methods: A total of 6264 children 1-9 years of age, residing in 64 clusters were registered into the study. The children were subjected to the standard tuberculin test using 1 TU PPD RT23 with Tween 80 procured from BCG Laboratory, Guindy and the maximum transverse diameter of the induration was measured at about 72 hours. Results: A total of 3157 children without BCG scar and 1520 with BCG scar was successfully test read. The prevalence of infection among children without BCG scar using the mirror image technique was estimated as 13.6% and the ARTI was computed at 2.6%. Using similar technique, the prevalence of infection among the entire study group-irrespective of BCG scar was estimated as 14.9% and the ARTI was computed at 2.8%. Conclusion: The findings indicate a high rate of transmission of tuberculous infection in rural areas of Kota and emphasise the need for further strengthening of tuberculosis control measures. [Indian J Tuberc 2004; 51: ] Key words: Tuberculosis, Tuberculin test, Prevalence, Infection, Annual risk. INTRODUCTION The scourge of tuberculosis (TB) continues to be an important cause of mortality and morbidity in India. Ironically, the quantum of epidemiological data on the disease is not commensurate with the magnitude of havoc wrought by it. This is attributable to incomplete reporting of the disease by the public health sector and almost non-existent reporting by the private health sector. Also, most epidemiological studies on TB have been confined to pockets of southern India. The epidemiological indicator, which is the cornerstone to gauge the situation of tuberculosis, especially in developing economies is the Annual risk of tuberculous infection (ARTI), since tuberculosis prevalence surveys are cumbersome and prohibitively expensive l. The ARTI is defined as the probability of acquiring new tuberculous infection or re-infection over a period of one year. It reflects the overall effect of various factors influencing the transmission of tubercle bacilli such as the burden of infectious cases in the community and the efficacy of the disease control strategies. The study, which for the first time systematically documented the enormity of suffering imposed by TB on the nation, was the National Sample Survey conducted by the Indian Council of Medical Research during Subsequent epidemiological studies on TB were predominantly from the southern regions of the country around the vicinity of the two bastions of excellence in TB research -National Tuberculosis Institute, Bangalore (NTI) and Tuberculosis Research Centre, Chennai (TRC). The lack of adequate epidemiological information on TB from most parts of the country led to the genesis of the nation wide tuberculin study to estimate the annual risk of tuberculous infection, which was conceptualized and implemented by NTI, Bangalore. In terms of the sheer magnitude of fieldwork that the study entailed crisscrossing the large expanse of the country, this study far surpassed all other tuberculin studies conducted in the past, in India. The fieldwork for the study was undertaken in the northern, western, southern and eastern zones of the country, the zones denoting the arbitrary geographical divisions having more or less equal populations. The study was designed to obtain the estimates of the prevalence of infection and thence * Paper presented at the 58th National Conference on Tuberculosis and Chest Diseases held in Mumbai from 1st to 4th January, Chief Medical Officer 2. Sr. Epidemiologist 3. Director 4. Statistical Assistant 5. Field Investigator National Tuberculosis Institute, Bangalore Correspondence: Dr. Preetish Vaidyanathan, CMO, National Tuberculosis Institute, Avalon, 8, Bellary Road, Bangalore (Karnataka) ntiindia@blr.net.in

2 124 PREETISH VAIDYANATHAN ET AL the ARTI in each of the four zones. Six districts were selected for the study in the western zone, namely -Kota, Junagadh, Jhabua, Thane, Nagpur and Ratnagiri. Though the sampling was not done to obtain the estimates specific to each district, this article reports on the study undertaken in the rural areas of Kota district. As the sample size comprising of children without BCG scar was considerably large in Kota district, it was considered prudent to disseminate the estimate of prevalence of infection and ARTI specific to rural areas of the district (Map ). The relevance of this data is accentuated by the fact that there was no prior epidemiological information on the situation of TB in the area. MATERIAL AND METHODS Study population The study population consisted of children 1-9 years of age. Older children were not included in the study as non-specific tuberculin sensitivity due to infection with environmental mycobacteria is more prevalent in them 3,4. The study was conducted in 64 rural and 19 urban clusters of Kota district. A cluster in a rural area was a village while in an urban area it was Map: Location of Kota in India denoted by a census enumeration block. In each cluster, 85 children were registered for the study, irrespective of the BCG scar status so that a minimum of 20 test-read children without BCG scar would be obtained, assuming 70% of the children to have BCG scar and a dropout of 20% between the registration and reading of tuberculin reactions. Field Procedures The study in Kota district was conducted during July-October The fieldwork in each cluster involved three activities -planning, registration and tuberculin testing, and reading. A planning visit was made to each cluster to inform the community on the nature of the survey and also to enlist their participation. During the planning visit, a rough sketch of the cluster indicating all lanes and hamlets was prepared after scouting around the cluster and a lane for initiating the fieldwork was selected at random. On the day of testing, children eligible for the study (>1 year and <10 years) were registered beginning from the first house of the lane selected for the study. Adjacent houses were visited following a specific direction until 85 children were registered for the study. The children were subjected to intradermal tuberculin test with 0.1 ml of tuberculin on the volar aspect of the left forearm. The tuberculin used was one tuberculin unit (1 TU) of purified protein derivative (PPD) RT 23 with Tween 80 (WHO standard tuberculin test) 5. A card was prepared for each child tested and the identification particulars recorded. A test was recorded as satisfactory if it raised a flat, pale pea sized wheal with clearly visible pits of hair follicles and no leakage of tuberculin. Also, the existence of BCG scar was noted by examining the arms of the children. Children with fever and history of skin rash and those on anti-tuberculosis treatment in the recent past were excluded from the study. Before administering the test, a written consent was obtained from the parent or guardian of the children. The reactions were read at about 72 hours after the tests. The reader palpated the maximum transverse diameter of the induration and recorded it in millimeters using a transparent scale. The presence of any unpleasant reaction manifested as

3 ARI IN RURAL AREAS OF KOTA 125 vesicles, bullae and necrosis was also recorded. The reader was unaware of the BCG scar status of children to eliminate any bias in reading of the reactions. The fieldwork was executed by a team of well-trained staff and was constantly supervised by experienced team leaders. The tuberculin testers and readers for the district were trained at NTI, Bangalore following a standard protocol. The data was double entered using a Foxpro based programme and validated. Also 95 smear positive cases of pulmonary tuberculosis were administered the tuberculin test (using the same batch of tuberculin used for the survey in Kota) within a week of diagnosis for corroborating the criteria used for estimating the prevalence of infection. Statistical Techniques The primary analysis was confined to successfully tuberculin test read children without BCG scar as tuberculin sensitivity due to BCG vaccination could interfere with the interpretation of the test results 4. Subsequently, the data obtained from all children irrespective of the BCG scar status was also analyzed. The histogram of tuberculin reactions size was plotted to identify the demarcation level (anti- mode or mode) attributable to infection with tubercle bacilli 6. The proportion of infected children in the rural areas of Kota was estimated as the weighted average of the cluster proportion, with the weight being the inverse of the initial probability of selection of the cluster. The formula used can be represented as 7 : P = i=1. n { p i / i }/ i=1. n {1/ i } Where P is the prevalence of infection, p i is the proportion of children infected in i th cluster and i is the initial probability of selection of the cluster i.e. ratio of the population of i th cluster to the rural population of the district. are the number of children infected and test read respectively in the i th cluster and w 1 is the weight (1/ i ). The ARTI was computed from the estimated prevalence of infection (P) using the relationship 8 : ARTI = 1 - (1-P) 1/A Where A is mean age of the test-read children. RESULTS The data was analyzed using SPSS software. The results pertaining only to the rural areas of Kota district are presented as the urban sample size of children without BCG scar was small (665 children). A total of 6264 rural children were registered for the study, of which 5759 were tuberculin tested and the reactions read in 4814 (84%). The proportion of children with BCG scar was 31.6% -34.0% in males and 29.0% in females. The primary analysis was confined to 3157 children without BCG scar after excluding those with scar (1520 children), those with doubtful scars (127 children) and those in whom the test had been performed unsatisfactorily (10 children) (Figure 1). Rural 6264 No. Tested 5759 No. Registered 8027 No. satisfactory Tested 4814 Urban 1763 The standard error was estimated as: BCG (-) 3166 BCG (+) 1521 BCG (+/-) 127 S = [c/ x i ] {[ w i y i 2 2P w i x i y i + P 2 w i x i2 ]/[c(c-1)] No. Test Read 3157 No. Test Read 1520 No. Test Read 125 Where c is the number of clusters, x i and y i Fig.1: Study population

4 126 PREETISH VAIDYANATHAN ET AL The frequency distribution of reaction size in children 1-9 years of age without BCG scar was observed to be bimodal with the mode of reactions suggestive of infection due to tubercle bacilli at 20mm (Figure 2). However, an antimode was not discernable on the plot. The modal value at 20mm was also vindicated by the same value obtained from the frequency distribution of reaction size of the rural areas of western zone (Figure 3). Also, an approximately similar mode at 22mm was found on tuberculin testing 95 smear positive patients (Figure 4). The weighted prevalence of infection by the mirror image technique was estimated at 13.6% (standard error 1.9%). The Annual Risk of Infection (ARTI) computed from the estimated prevalence was 2.6%.The mean age of the children was 5.6 years % of reactors Tuberculin reaction in mm Fig. 2: Frequency Distribution of tuberculin size in childrens (1-9 years) without BCG scar of reactors 10.0 Western Zone (Rural) 5.0 Kota (Rural) T uberculin reaction in mm Fig. 3: Frequency Distribution of tuberculin size in childrens (1-9 years) without BCG scar - Kota (rural) and Western Zone (rural)

5 ARI IN RURAL AREAS OF KOTA 127 About 6.5% of children of the age group of 1-4 years were infected while 18.4% were infected in the age group of 5-9 years. The ARTI computed from the prevalence of infection estimates for these age groups were 2.1% and 2.7% respectively (Table 1). To compare the proportion of infected children according to the BCG scar status, the modal value at 20 mm was applied as depicted in Table 2. These proportions were found to be significantly different in 1-4 years age group and statistically similar

6 128 PREETISH VAIDYANATHAN ET AL in 5-9 years age group. However, in the overall study group comprising 4677 children 1-9 years of age irrespective of BCG scar status, 14.9% (standard error 1.7%) were found to be infected and the computed ARTI at 2.8% was similar to that computed in children without BCG scar (Figure 5). DISCUSSION The results of the study provide vital information on the epidemiological situation of TB in rural areas of Kota district. No study of this nature had been conducted in the area in the past. The study period in Kota almost coincided with the time when the Revised National Tuberculosis Control Programme (RNTCP) was introduced in this area. Perhaps this data could serve as baseline for evaluating the impact of the RNTCP in rural areas of Kota district. The epidemiological situation of tuberculosis in Kota is the manifestation of the poor performance of the National Tuberculosis Programme (NTP), which was in vogue for several decades. The estimated prevalence of infection of 13.6% in children of ages 1-9 years in Kota was high in comparison to that obtained from the other districts of the western zone selected for the study 9. The other districts selected were Junagadh (Gujarat), Nagpur, Ratnagiri and Thane (Maharastra) and Jhabua (Madhya Pradesh). The higher prevalence of infection in Kota could perhaps also be attributable to the low Human Development Index (HDI) of Rajasthan (ranked 9th) compared to the other states of Maharastra (ranked 4th) and Gujarat (ranked 6th) of the western zone in which the study was conducted 10. The proportion of infected children obtained from the study in Jhabua district (Madhya Pradesh) was also high which was in tune with the low HDI of Madhya Pradesh (ranked 12th) 10. It may be mentioned that the HDI is a composite of variables capturing attainments in three dimensions of human development, namely economic, educational and health. The proportion of children with BCG scar was also low in Kota % of reactors T ube rculin re action in mm Fig. 5: Frequency Distribution of Tuberculin reaction in 1-9 years children - irrespective of BCG scar

7 ARI IN RURAL AREAS OF KOTA 129 district compared to that in Junagadh, Nagpur, Ratnagiri and Thane districts 9. These statistical data tend to confirm the impression that poverty and TB are intertwined. The ARTI of 2.6% in Kota was much higher than the average 1.4% estimate pertaining to rural areas of western zone 11. The ARTI of 2.6% in Kota could translate to an incidence of 130 new smear positive cases per lakh population. This is in line with the parametric relationship between the ARTI and the incidence of new smear positive tuberculosis cases as propounded by Styblo 12. It is not possible to comment on the impact of HIV on the tuberculosis situation in Kota due to lack of data from the past. The only noteworthy study on the ARTI in Rajasthan before this nation wide study was that conducted in a sub- division of Bikaner district 13. With the increase in vaccination coverage, studies in the future that exclude children with BCG scar from epidemiological surveys may not reflect a representative sample. The necessity and feasibility of including children with BCG scar for estimation of ARTI has been elucidated in earlier studies conducted by National Tuberculosis Institute, Bangalore The results of this study also imply that children with BCG scar, especially in the 5-9 years age group, may be included for tuberculin surveys for the estimation of the ARTI. A limitation of the study could have been the non-availability of vaccination cards for verification of the BCG vaccination status since BCG scar may not be perceived in a proportion of BCG vaccinated children 18,19. However, this does not seem to affect the study results since the estimated ARTI in the overall study group was similar to that estimated among children without BCG scar. The assessment of the epidemiological situation of TB in a vast country like India is fraught with myriad operational difficulties. The study was successful due to the dedicated efforts of the field staff, who rigorously adhered to the work instructions and maintained high standards of research discipline. The cold chain of tuberculin was meticulously maintained. To minimize inter reader variation in the reading of reactions, only a single reader was deployed for the study in Kota. The high prevalence of infection observed in rural areas of Kota district can only be redressed by intensifying the TB control strategies. It is heartening to note that the performance of the RNTCP in Kota provides grounds for hope as the sputum conversion rate of new smear positive cases in the district was 94% (2002) and the cure rate 88% (2001) 20. However, there is room for improving case finding by forging partnerships with the private sector and non-governmental organizations. The high ARTI in Kota implies that the incidence of new cases will continue to be high in the near future and that no reduction in incidence can be expected in a short term. Nevertheless, successful implementation of the RNTCP has the potential of tuberculosis control being a reality. ACKNOWLEDGEMENTS The authors express their gratitude to the valuable suggestions offered by the members of the Technical Co-ordination Committee of the National Tuberculosis Institute, Bangalore. The services offered by the officials of the Epidemiology section, namely Mr. Narayan Prasad, Mr. Magesh, Mrs. Uma Devi in ensuring successful rendition of the fieldwork is laudable. The untiring efforts of Mr. Sanjay Singh and Mrs. K. Rekha in the preparation of the manuscript are also acknowledged. Last but not the least, the support, encouragement and guidance of the Director General of Health Services, who was the Chairman of the Steering committee and the Deputy Director General of Health Services (TB) in ensuring the smooth execution of the study, is warmly appreciated. REFERENCES 1. Arnadottir T, Rieder H L and Trebueq A. H T Waaler. Guidelines for conducting tuberculin skin test surveys in high prevalence countries. Tubercle and Lung Dis. 1996; 77: Suppl Indian Council of Medical Research. Tuberculosis in lndia- A Sample Survey, , Special Report Series No. 34, ICMR, New Delhi. 3. Chakraborty A K, Ganapathy K T, Nair S S, Kul Bhushan.

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