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8. Discussion


The nation wide study was conducted to assess the present epidemiological situation of tuberculosis in different parts of India. The ARTI was selected as the study parameter as it is the most reliable index of TB situation in the community. India being a vast country, a single estimate of ARTI for the whole country might not provide the true picture of the disease situation. On the other hand, the time and resources required are too prohibitive to have state specific ARTI estimates. The country was therefore stratified into four zones and the study was designed to estimate average annual risk of tuberculous infection in each of these zones. This would provide a reasonably fair assessment of the disease situation in different parts of the country.

In each of the north, south and west zones, six districts were selected for operational convenience. In east zone, eight districts were selected specifically to accommodate larger representation from the northeastern states.

The study was conducted among children below 10 years of age (excluding infants), since the estimates of risk of infection obtained among this young age group reflect on relatively recent disease situation. The ARTI was estimated from the tuberculin test results among children without BCG scar, in order to eliminate the influence of BCG-induced tuberculin sensitivity, if any. However, children with BCG scar were also registered and subjected to tuberculin testing, which facilitated better community participation. This also helped in avoiding any possibility of bias in BCG scar reading by the field workers. The prevalence of BCG scar had been observed to be about 50% in most of the studies conducted in recent times in various parts of the country. Still, a higher prevalence of BCG scar was presumed in order to decide on the number of children to be registered in each cluster, so as not to err on the wrong side. In the present study, about 45% of the children were found to have BCG scar in the north zone and 64% in south zone. The proportion of children with BCG scar was found to be 52% in west and 51% in east zone. The number of test read children without BCG scar was therefore, higher than the estimated sample size in each of the zones. In all the zones, the BCG scar ratio was higher in urban areas compared to rural areas.

The proportion of test read children in individual age-group (1-4 year, 5-9 year) and each sex was similar to such porportions as obtained during the census.

1 TU PPD RT 23 with tween 80 procured from BCG Lab, Guindy was used in the study. Most of the previous studies in India have been conducted using this dose and product. A review of these studies and a series of studies undertaken to compare this dose and product with a higher dose and dilutions prepared at SSI justified the continued use of 1 TU PPD RT 23 dilutions prepared by BCG Lab, Guindy.

The prevalence of infection among children is a reflection of the disease situation in the community since it depends not only on the load of infectious cases in the community but also on the efficiency of case finding and treatment programmes. Two statistical methods are generally used for its estimation. One method is based on identifying a cut off point (antimode) from the frequency distribution of reaction size and all reactions greater than or equal to this cut off point are considered to be due to infection with tubercle bacilli. The other method is based on identifying the mode of reactions attributable to infection with tubercle bacilli and obtaining the estimates by mirror-image technique. In the present study, the estimations were made by using both the methods. It is noteworthy that the modes and antimodes of reactions attributable to infection with tubercle bacilli did not differ significantly in the four zones. The modes were observed at 20 mm in north, west and east zones and 19 mm in south zone. The anti-modes varied from 14 to 16 mm in rural areas and 12 to 16 mm in urban areas of different zones.

Based on the criteria defined as above, the prevalence of infection among the age group studied was observed to be the highest in the north zone (method I-10.3%, method II-10.5%) followed by west zone (method I-9.3%, method II-8.5%). It was lower at 6.9% in east zone (both methods) and the lowest in the south zone (method I-6.1%, method II-5.9%).

The prevalence of infection represents the cumulative effect of the risk of infection experienced by the study group. The ARTI computed from the prevalence estimates denotes the average annual risk of infection experienced by the study group in their years of exposure. The ARTI in different zones was found to be lowest in south zone (method I- 1.1%, method II-1.0%). It was higher in east zone (1.3% by both methods) and highest in west (method I-1.8%, method II-1.6%) and north zones (1.9% by both methods). The average ARTI in the country as a whole was estimated at 1.5%, on pooling the zonal results.

The ARTI rates estimated from previous studies in different areas of India are summarized in Fig 8.1. Most of these studies were conducted in defined geographical areas around the national level TB institutes located in south India. Therefore, the results of the present study provide for the first time vital information on the prevailing epidemiological situation of TB across the country. The tuberculosis situation in most parts of India continues to be grave with an average 1500 persons out of every 1,00,000 acquiring new tuberculous infection each year and potentially at risk of breaking down into disease anytime in the future. However, no conclusion can be drawn on the trends from the past for want of sufficient data as stated above. The current ARTI rates in most of the developed countries are however less than 0.1%.

Another important conclusion of the study was that the TB situation is worse in urban areas as compared to rural areas. The estimated ARTI rates in urban areas were rather too high at 2.6% in north zone, 1.8% in south zone, 2.4% in west zone and 1.7% in east zone as estimated by method I. The ARTI rates in rural areas were 1.6% in north zone, 0.8% in south, 1.5% in west and 1.2% in east zone, as estimated by the same method. The worse TB situation in urban areas might be due to poorer organization of anti-TB services with multiplicity of agencies and services. A large proportion of patients seeks care from the private practitioners, most of whom do not adhere to the national guidelines in case detection and treatment. In addition, the mushrooming of slums with poorer living conditions facilitates faster transmission of infection. The influence of HIV epidemic on TB situation is also likely to be more in urban areas.

The results of the present study indicate that TB continues to be a major public health problem despite the implementation of NTP since 1962. This is mainly attributable to unsatisfactory performance of NTP during the last four decades. The efficiency of case finding had been less than one third of the expectation. The potential of sputum microscopy to detect the most infectious TB cases was never put to its optimum use. The unsupervised chemotherapy and erratic drug supply led to high rates of default and less than half of the diagnosed cases completed the prescribed duration of treatment. The program was not accorded the deserving priority by the health administrators, planners, bureaucrats and the leaders alike. However, the introduction of DOTS strategy in the form of RNTCP has raised hopes of controlling TB in the country. The DOTS strategy has been reported to have reduced the disease burden in many countries including those which had experienced a resurgence of TB since mid 1980s and early 1990s in the wake of HIV epidemic and other socio-demographic factors. In India too, the cure rates achieved under RNTCP were in excess of 80% in most of the areas. However, there is much scope for improvements in the case finding efficiency under RNTCP. Extrapolating the parametric relationship between ARTI and the incidence of smear positive cases derived by Karel Styblo, every one percent of ARTI would correspond to a minimum of about 50 incident cases of smear positive pulmonary TB per 1,00,000 population per year. This relationship was derived in the pre-chemotherapy era and may therefore be limited in its relevance in the present context. Nevertheless, it remains the most commonly used tool for estimating disease incidence for the purpose of planning control activities. A rough estimate of the expected average incidence of smear positive cases in different zones, based on the estimates of ARTI obtained in the present study are presented in table 8.1. The average case detection of new smear positive cases in the areas covered by RNTCP in these zones as well as in NTP areas during the year 2002 is also presented. The case detection rates have improved further during the year 2003. However all efforts must be made to provide access to the DOTS programme for each and every TB case in the country. The districts where the RNTCP is being implemented covered more than half of the country's population as on December 2002. Efforts are being made to introduce RNTCP in the remaining districts at the earliest possible. However, the accessibility to the DOTS strategy needs to be enhanced by involving the non-governmental organization and the private sector within the already implemented districts. They should be sensitized and persuaded to follow the national guidelines in case detection, treatment regimen and direct observation of drug consumption by the patients. All support in this regard should be provided by the public health sector. The ARTI estimates obtained in the present study also imply that the incidence of fresh cases will continue to be high in the years to come and a drastic reduction in disease situation cannot be expected in a short time. Therefore the efficiency of TB control measures will have to be sustained over a prolonged period.

It may not be inappropriate to mention here that many of the countries were able to reduce their TB problem to a very significant extent even before the anti-TB drugs came into being. This was facilitated by all round improvements in the living status of their populace facilitated by general improvements in the primary health care system, improvements in economic and nutritional status as well as the housing conditions. Therefore, all efforts must also be made to improve significantly the delivery of primary health care system in addition to improving the living conditions for the masses.

Table 8.1 : Expected incidence of new sputum smear positive pulmanary TB cases and case detection rates
  () :95 % Confidence interval
* Mid-Year population is taken as the denominator.

Fig 8.1 :Annual Risk of tuberculosis infection in India - previous studies