The Effects of the Diminished Incidence of Primary Infection on the Tuberculosis Control Program

Abstract

1) Primary tuberculous infection is the fountainhead of all tuberculosis. 2) Most attempts to control this disease have been directed against gross lesions while primary infections were unmolested and even encouraged. 3) Early in the 20th century in the United States a small group of physicians began to advocate protection of children from primary infections. 4) This was strenuously opposed on the ground that such infections protect against subsequent clinical disease. 5) The opposition was partially overcome and sanatoriums were built for the isolation of persons with contagious disease. A nationwide educational campaign was instituted. Veterinarians organized a national tuberculosis eradication program which was a potent factor in preventing primary infection in people and animals. 6) Accomplishments were phenomenal. Mortality rates for all ages in the United States decreased 82 per cent between 1915 and 1949, and 94 per cent among infants during the same period. In New York City, among children under 15 years old the mortality rate decreased approximately 94 per cent between 1915 and 1948. The primary infection attack rate tumbled to less than 1 per cent per annum in many places, a small fraction of 1 per cent in others, and primary infections disappeared among children of many entire schools. Condemnation of carcasses of cattle to rendering tanks decreased 98.6 per cent between 1917 and 1951. By 1951 the incidence of tuberculous infection among cattle had decreased to 0.14 per cent. In large areas primary infection has been eradicated from cattle. 7) As the work progressed, erroneous theories were replaced by facts, as follows: (1) The bovine type of tubercle bacillus long thought to be of low virulence for man produces as incapacitating and killing disease in people as the human type of bacillus. (2) The bovine type of bacillus, as it occurred in dairy products so highly recommended to protect children against later clinical disease, was found not only unsafe, but possesses no dependable immunizing quality. (3) Protecting people and animals from primary infections would create “virgin soil” for later attacks of tuberculosis was found to have no factual basis. Both people and animals respond to primary infection in adulthood as they do in the early years of life. 8) The diminished incidence of primary infection has afforded the opponents of tuberculosis the best ventage ground of all time. The tubercle bacillus has been brought into bold relief where it can be attacked directly by refined methods. 9) This situation permits extensive use of the tuberculin test by which the presence of primary infection can be detected within two months after the invasion with tubercle bacilli occurs. Periodic x-ray film inspection of chests of tuberculin reactors locates chronic reinfection type of pulmonary lesions on an average of two and one-half years before they cause symptoms and usually before they liberate tubercle bacilli. Lesions found in this stage of evolution can usually be successfully treated in much less time than those which have become more advanced and are contagious. 10) This method has been in use sufficiently long and in large enough areas to establish its efficacy. It is the only method known today by which tuberculosis can be eradicated. 11) By isolating lepers in leprosariums to protect the public against contagion leprosy was eradicated from England and most of Western Europe by the end of the 16th century. Eradication of tuberculosis can be accomplished as it was in leprosy by preventing primary infections from developing in uninfected people and animals. Such infections have already been prevented in a large segment of our human and animal population. Continuation of the present methods is adequate. Eradication of tuberculosis in any community or nation can be announced, not when people and animals stop falling ill and dying, but when primary infections have vanished.