Abstract

PIP: This is a review of the epidemiology of tuberculosis in children covering the classical aspects of sources, prevalence, annual risk, risk of active disease, frequency of childhood tuberculosis (TB) in the population, and mortality, ending with descriptions of the course of active TB. post-primary pulmonary disease, disease of other systems, and the impact of control measures and poverty. The source of TB is always expectorating adults with active TB-positive sputum. The prevalence of TB in children in developing countries is estimated at 10-20%. Each untreated source infects about 10-13 new persons per year, yet, if treated, that person would only infect 2-3 people per year. The risk of a TB infection evolving into an active infection is about 10% and is highest in the first 2 years after primary infection. The frequency of childhood TB in the population ranges from 2.5% in Japan, to 18.5% in Tanzania with its younger population. The morbidity rate varies with ethnic and socioeconomic group; for example, from 1.3% in White to 17.2% of American Indian children up to age 4 in the U.S. In children, TB rarely follows the typical course seen in adults; post-primary pulmonary disease. Children under 2 often develop hematogenous complications of TB, i.e., extrapulmonary disease. When children get pulmonary disease, they rarely have cavitation, so they do not expel infective sputum. Thus, only 3-13% of children are smear-positive, while 29% may have positive cultures. In children, primary infection may appear as visible mediastinal lymphadenopathy. The highest mortality rates are in children under age 5, mostly from TB meningitis. Case-finding, followed by chemotherapy, has the greatest impact on control of the disease. BCG vaccination of infants prevents active primary disease in the young, but neither BCG nor chemoprophylaxis of children has any effect on controlling the spread of TB in the population. It is likely that HIV disease and the growth of poverty will increase the incidence of TB in developing countries.