India is classified along with the sub-Saharan African countries to be among those with a high burden and the least prospects of a favorable time trend of the disease as of now (Group IV countries). The average prevalence of all forms of tuberculosis in India is estimated to be 5.05 per thousand, prevalence of smear-positive cases 2.27 per thousand and average annual incidence of smear-positive cases at 84 per 1,00,000 annually. The credibility and use of the estimates are discussed in detail. Reports on recent studies on the time trend of the disease from some areas in India , e.g., Chingleput in Tamil Nadu are discussed. They confirm the slow downward trend over a fairly long period of observation, as in the rural areas around Bangalore . It also outlines the serious escalation of disease burden in a tribal population group in Car Nicobar over a period 1986-2002, and highlights the nature and extent of the emerging threats. Some epidemiologists forecast a rise of 20 per cent in incidence in the next 20 yr, for India , with a cumulative rise of 46 million cases of tuberculosis during that period, largely as a consequence of HIV epidemic.

The Governmental efforts at intervention through Revised National Tuberculosis Control Programme (RNTCP) and at monitoring the epidemiology of intervention through organizing routine reporting are highlighted, and data are presented and evaluated on these. RNTCP needs to be used as an effective instrument to bring a change in epidemiological situation, through fast expansion and achievement of global target. The present review describes the global tuberculosis situation, and views it in the context of the goal of the anti-tuberculosis intervention activities. It presents the epidemiological situation in India , comments on the current trend and discusses the efforts taken towards making projections on the likely burden of disease in India over time. An increasing morbidity and mortality from human immuno deficiency virus (HIV) was also tuberculosis (TB) in the near future in Africa is forecast for found to be rising, being 2-10 times greater for the world at large, with the number of newly 1997 estimates, than for19902. The association with occurring cases predicted to increase from 7.5 million HIV and increasing multi drug resistant tuberculosis a year in 1990 to 8.8, 10.2 and 11.9 million in the (MDRTB) appears to be a serious issue, especially years 1995, 2002 and 2005 respectively; an increase for the developing nations. amounting to 58.6 per cent over a 15-yr period. The estimates were subsequently found to be appropriate Zaki in 1983, had commented that “The for the year 2000 using a new method. The international tuberculosis situation is complicated by proportion of tuberculosis cases co-infected with the growing impression that tuberculosis is no longer present.

Host-related and environmental factors for tuberculosis have usually been investigated separately using different study designs in Africa . Joint investigation of the genetic, immunologic, and environmental factors at play in susceptibility to tuberculosis represents an innovative goal for obtaining a better understanding of the pathogenesis of the disease. In this paper, the authors describe methods being used to investigate these points in a West African study combining several designs. Patients with newly diagnosed smear-positive cases of tuberculosis are recruited. The effect of host-related factors is assessed by comparing each case with a healthy control from the case's household. The role of environmental factors is estimated by comparing cases with randomly selected community controls. The frequencies of candidate gene variants are compared between cases and community controls, and results are validated through family-based association studies. Members of the households of cases and community controls are being followed prospectively to determine the incidence of "secondary" tuberculosis and to evaluate the influence of geographic and genetic proximity to the index case. This type of design raises important methodological issues that may be useful to consider in studies investigating the natural history of infectious diseases and in attempts to disentangle the effects of environmental and genetic factors in response to infection.

Few studies have investigated the risk factors for tuberculosis (TB) infection in highly endemic countries. The study conducted in The Gambia, in which a tuberculin skin test (TST) was performed in members of the households of 315 smear-positive pulmonary TB cases and 305 community control subjects. The risk of being TST positive (10 mm or more) was higher in contacts of cases than in contacts of control subjects. It increased with age, male sex, and duration of stay in the household but was not associated with the presence of a bacilli de Calmette-Guérin scar. Within the households of the TB cases, the risk of TST positivity was higher in males and was increased with age, social proximity to the case, and the radio logic extent of the disease in the case's chest X-ray. Adjusting on these, the risk of TST positivity was higher in first-degree relatives compared with more distant relatives and non-genetically related household members, but the effect was not statistically significant. In highly endemic areas, the risk of TB infection in contacts of TB infectious cases is associated with age, sex, intensity of exposure to the case, and severity of disease in the case, but it is possible that genetic factors contribute to the susceptibility to Mycobacterium tuberculosis infection.

Links:

1. Brown TB/HIV Research Laboratory
 

References:

1. Investigation of environmental and host-related risk factors for tuberculosis in Africa . I. Methodological aspects of a combined design.
Lienhardt C, Bennett S, Del Prete G, Bah-Sow O, Newport M, Gustafson P, Manneh K, Gomes V, Hill A, McAdam K