An Overview on Epidemiology of Tuberculosis

Abstract

Tuberculosis (TB) is a progressive granulomatous infectious disease caused by the gram positive, acid fast bacilli classified under the genus Mycobacterium. Tuberculosis in human is mostly by Mycobacterium tuberculosis and primarily affects lungs causing pulmonary tuberculosis. It can also affect intestine, meninges, bones, joints, lymph nodes, skin and other tissues of the body causing extra-pulmonary tuberculosis. Human TB is transmitted mainly through droplet infection and droplet nuclei. Infection of human with M. avium and M. africanum is very rare. M. microti is not known to cause TB in human, while M. bovis has a wider host range. Human may be infected by M. bovis through milk and milk products or meat of an infected animal. It is estimated that in some developing countries up to 10% of human tuberculosis is due to bovine TB. Tuberculosis causes more than 2 million deaths annually and the death toll is worsened by the emergence of drug resistant Mycobacterium tuberculosis. The South East Asia Region accounts for 39% of global burden of TB in terms of incidence. It is estimated that about 3.4 million new cases of TB continue to occur each year in this region, most of them in India, Bangladesh, Indonesia, Myanmar and Thailand. Tuberculosis is a social disease with medical aspects. It has also been described as a barometer of social welfare. The social factors include poor quality of life, poor housing, overcrowding, population explosion, under-nutrition, smoking, alcohol abuse, lack of education, large families, early marriages, lack of awareness regarding cause and transmission of TB. These factors are interrelated and contribute to the occurrence and transmission of tuberculosis. It is estimated that approximately 10% of total TB is occurred in children. Childhood deaths from TB are usually caused by tuberculous meningitis or disseminated disease. The number of individuals infected with both HIV and TB is increasing worldwide. The HIV affects the body's immune system and enhances the speed at which TB progresses from a innocuous infection to life threatening condition. TB is a major cause of death of HIV positive individuals. Diabetes has been shown to be an independent risk factor for tuberculosis in community based studies from south India and multiple studies globally. It is suggested that diabetes accounts for 14.8% of all tuberculosis and 20.8% of smear positive TB. Understanding of epidemiology of tuberculosis is essential for its effective control. This review tried to summarize the epidemiological aspects of tuberculosis in global, regional and Bangladesh perspectives. For this review article, data available in books and at the official websites of WHO, MBDC, NTP, DGHS, The Ministry of Health and Family Welfare, Government of Bangladesh were consulted through PubMed central and Google scholar search engines. This paper has been written with an aim to offer general education to health professionals, policy makers, patients and the public.