Serodiagnosis of tuberculosis.

In the developing countries, which have the majority of the world's population, tuberculosis is one of the most important infectious diseases, causing illness and death on a very large scale. In these counlries there ha<; been little or no decline of this disease during recent years and improved conlrol programmes and case identification are therefore imperative. In the developed countries tuberculosis is no longer among the most common diseases but it often causes diagnostic problems. More rapid methods for diagnosis would be a great advantage. Thus, a serodiagnostic test for tuberculosis would be extremely useful throughout the world. It would speed up diagnosis, and would be valuable when bacteriological proof is difficult to obtain, or when tuberculosis is part of a differential diagnosis. Attempts to develop serodiagnostic tests for tuberculosis have been made for more than ninety years. In 1898 ARLOING and CoURMENT published studies on agglutination of Mycobacterium tuberculosis cells using sera from patients with tuberculosis [1, 2]. Since that time a large number of publications have been made in this field (see review articles (3, 4]) and most serological techniques have been utilized. Most of the studies demonstrate similar results. They show that sera from patients with tuberculosis contain antibodies against the tubercle bacillus. As a group the tuberculosis patients have much higher antibody titres than healthy controls or patients with other diseases. The variations within the groups are large, however, and the groups do overlap. False positives and false negatives occur frequently. The tests therefore have comparatively little diagnostic value and serodiagnostic tests for routine diagnosis are not in general use. There are several reasons for the failure to produce a serodiagnostic test which is both specific and sensitive enough. Most tests developed so far have been based on antigen preparations such as culture filtrates, purified protein derivatives (PPD) or whole cells, and such preparations always contain many epitopes. Mycobacteria are rich in cross-reacting antigens and M. tuberculosis is known to share antigens with other species of Mycobacterium as well as with nocardiae, corynebacteria, rhodococci etc. [5). This may be the cause of the false positive tests amongst the controls, since these organisms abound in the enviroment and/