Public health issues of tuberculosis

Abstract

~ ransmission of tuberculosis (TB) is a paradox--at once extremely simple, yet extraordinarily complex. ''1 Tuberculosis is one of the most common infections in the world. It is estimated that i.5 billion people--almost one third of the world's population-are infected with the tubercle bacillus. Thus the human race makes up a large reservoir of infection which, acting as a slow time bomb, continues to provide a steady number of new cases of active TB. Almost every new infection is the result of airborne transmission. Although a single inhaled tubercle bacillus can infect a susceptible host, TB is not considered infectious when compared to varicella, measles, and other diseases caused by airborne viruses. Here is the paradox. Although an unfortunate medical student or emergency room nurse may become infected after brief contact with his/her first contagious case, scientific literature since the 1930s indicates that when TB was common and not effectively treated, it required an average of 6 to 8 months' exposure for conversion of skin tests of health care personnel in sanitoriums. ~ Perhaps this led to the mistaken belief that TB transmission requires prolonged exposure. Although we should discourage the health care worker's terror of catching the disease, we must dispel the old myth that TB is difficult to contract. The commonly held belief that tubercle bacilli dry out and die rather quickly once they are expelled from the human body is not true. Exhaled organisms are viable and infective for prolonged periods of time. 3 The situation of a susceptible host with human immunodeficiency virus (HIV) infection combined with the possibility of multidrug-resistant strains of TB poses a serious threat to health care workers as well as to persons living in highly endemic areas. Airborne transmission of TB occurs through droplet nuclei that may remain suspended in the air for several hours. The probability of transmission depends on (1) infectiousness of the source case, (2) environment in which exposure occurs, and (3) duration of exposure. The potential communicability of source-case infection depends on the bacterial load and number of droplet nuclei expelled by the infected per