Tubercolosis: a neglected disease strikes back

Abstract

l 'n recent years tuberculosis has been considered a minor, and .decreasing, problem in industrialized countries despite the fact that it has remained a severe problem for numerous developing countries. Now this neglect is striking back: tuberculosis is on the increase all over the world, not only in developing but also in industrialized countries. Here we report on the World Congress on Tuberculosis held in Bethesda, MD, USA, in November 1992. Worldwide, 60 million people suffer from active tuberculosis; annually, 10 million new cases arise and 3 million people die. Thus, tuberculosis is responsible for more than 6% of all deaths and 25% of all preventable deaths, in short, more people die of infection with Mycobac ter ium tuberculosis than of any other single infectious agent. There is no question that tuberculosis is primarily a problem in developing countries, in which 95% of all cases occur. Yet, the steadily declining incidence in many industrialized countries has been reversed during the past two years. In 1992 about 26 000 active cases of tuberculosis were reported in the USA, which represents an 18% increase since 1988. Similar increases are being observed in many European countries: compared to the lowest recorded incidences between 1985 and 1988, the numbers of active cases in 1990-1991 have increased by 33% in Switzerland, 30% in Denmark, 20% in Norway, 18% in Ireland, 17% in Austria, 9% in The Netherlands, 5% in Sweden and 4% in the UK (C.L. Hu, World Health Organization, Geneva, Switzerland). Tuberculosis is transmitted aerogenicaUy and individuals of normal immune status do not in general develop disease symptoms. Rather, the bacteria establish a stable infection that stimulates the host immune system. Infection and T cell activation can be demonstrated by the positive delayed-type hypersensitivity reactions to tuberculin. Frequently, a labile balance develops between host defence mechanisms and survival of M. tuberculosis such that the infection can later lead to full-blown disease, typically following general or specific depression of the immune response. According to World Health Organization estimates, 1.7 billion individuals (one third of the total world population) are infected with M. tuberculosis and hence at risk of reactivating tuberculosis. Two risk factors contribute to the distribution of tuberctflosis: (1) the number of infected individuals who may develop the disease in the future but do not contribute to its spread, and (2) the number of individuals who have active tuberculosis and are contagious. Rapid case detection and initiation of therapy are not only of prime importance for the infected individual but also for the control of transmission. Obviously, the global HIV/ AIDS endemic has had a major impact on the current tuberculosis situation, particularly in developing countries. During 1984-1991, reported cases of tuberculosis more than doubled in Zambia and tripled in Malawi. It has been estimated that worldwide 4.4 million people are co-infected with HIV and M. tuberculosis, of which half a million have active tuberculosis (by the year 2000 this number may