Tuberculosis

Tuberculosis

Introduction

Tuberculosis (TB) is an ancient disease, with evidence found in human remains dating back over 9000 years, to the Neolithic era. 1 It was identified and described by Hippocrates as early as 460BC, and continued to be documented in such places as ancient Rome, Egypt, India and China. 2 3 4 5

The disease can be caused by different mycobacterium such as Mycobacterium bovis, M. africanum, M. canettii, M. microti, and most commonly, M. tuberculosis; although the five are highly similar and are together termed the Mycobacterium tuberculosis complex (MTBC). Recently, two additional organisms. Mycobacterium pinnipedii and Mycobacterium caprae have also been implicated with the disease in humans. 6, 7 Members of the MTBC are gram-positive, long, rod-shaped bacterium with unique characteristics such as an exceptionally slow growth rate and a high content of lipids in their cell wall which provide protection against degradation and may account for their persistent survival in the environment even after the death of a host. 8

Active tuberculosis only develops in about 10% of infected persons, remaining dormant in the rest; although the latent infection may later progress to active disease years later, especially in immune-compromised individuals. 9 Infection by MTBC may involve any organ of the body, but clinical presentation is most common in the lungs (pulmonary TB). General symptoms include fever, loss of appetite, weight loss, fatigue and severe cough with bloody sputum (hemoptysis) which may lead to death if untreated. 10 Mortality rates without treatment are high: in a study of natural history of TB in HIV-negative patients, 70% died within 10 years. 11 Tuberculosis remains a major health problem in the world...

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...as better ventilation, negative pressure rooms and the use of UV light for disinfection, nosocomial transmissions continue to post a problem possibly because they are iatrogenic and cases may be missed due to underdiagnosis. 16

Infectiousness

Infection rates of TB are high, especially when in frequent or close contact with individuals with active TB. One study estimates an infection rate of about 22% and a diagnosis with positive sputum smear is the strongest indicator of infectiousness. 19 However, contrary to common belief, sputum smear-negative patients are also infectious, with a study in San Francisco attributing 17% of transmissions to such cases. 20

Researchers have also identified a list of other factors associated with TB transmission such as environmental, organism and host factors, but these unfortunately, are outside the scope of the present paper. 16