Abstract
The evidence regarding the transmission of tuberculosis and risk of infection and disease in several specific clinical situations has been reviewed. There is considerable epidemiologic evidence that contagiousness is not an all-or-nothing phenomenon and is affected by several factors, only one of which is the bacteriologic status of the patient’s sputum. Although untreated smear negative, culture positive patients are less contagious on average, they still may transmit infection to their close and casual contacts. Compared with contacts with tuberculin conversion, persons who are already tuberculin positive have much lower risk of developing active tuberculosis after exposure, and persons with prior BCG vaccination are at somewhat lower risk. Preventive therapy will be of less benefit, but should still be recommended for contacts who are heavily exposed or are immune compromised. Epidemiologic studies using RFLP techniques could provide more precise answers to the questions in this review.
Résumé
On a passé en revue les données concernant la transmission de la tuberculose et le risque d’infection et de maladie dans plusieurs situations cliniques particulières. Il existe un nombre considérable de données épidémiologiques montrant que la contagion n’est pas un phénomène clair et net et qu’elle est influencée par plusieurs facteurs, l’état bactériologique des expectorations n’en constituant qu’un parmi d’autres. Bien que (de frottis d’expectorations négatif) les patients positifs à la coproculture soient moins contagieux en moyenne, ils restent susceptibles de transmettre l’infection à leurs proches et à ceux avec lesquels ils ont de simples contacts. En comparaison avec les sujets contacts avec conversion tuberculinique, les personnes qui réagissent déjà positivement à la tuberculine ont un nettement moins grand risque de développer une tuberculose évolutive après exposition, et les personnes vaccinées au BCG ont moins de risques également. Bien qu’offrant moins d’avantages, une thérapie préventive doit tout de même être recommandée aux sujets contacts très exposés ou à ceux dont l’immunité est déprimée. Les études épidémiologiques se servant des techniques du polymorphisme des sites de restriction pourraient permettre d’obtenir des réponses plus précises aux questions soulevées dans cet article.
Footnotes
Supported by the Fonds de Recherche en Santé du Québec
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