Effect of treatment on contagiousness of patients with active pulmonary tuberculosis.

In view of the important consequences with regard to policies for respiratory isolation of hospitalized patients with active tuberculosis, the duration of contagiousness after initiation of effective therapy was reviewed. All relevant English-language literature was reviewed to identify in vitro, animal experimental, and epidemiological evidence regarding contagiousness of patients with active tuberculosis after initiation of therapy. Based on in vitro evidence of numbers of tubercle bacilli initially present and rapidity of reduction with therapy, it can be predicted that patients whose respiratory secretions are initially smear-negative but culture-positive should no longer have viable bacilli detectable by culture within 2 weeks. Based on the same evidence, it can be predicted that, after 2 weeks of therapy, almost all smearpositive patients will remain culture-positive, and more than one half will remain smear-positive. There are few epidemiological studies of this issue, most of which have had major methodological weaknesses. None of the results from these studies can be considered relevant to the hospital environment, where the majority of workers are uninfected and patients are potentially immunocompromised. Animal and in vitro evidence suggest that patients with active tuberculosis remain contagious at least 2 weeks after the initiation of therapy. Patients with smear-positive disease are likely to be contagious much longer. There is no relevant and valid epidemiological evidence regarding this issue (Infect Control Hosp Epidemiol 1997;18:582-586). A combination of the resurgence of tuberculosis (TB), the human immunodeficiency virus epidemic, and emergence of multidrug-resistant strains has resulted in more than a dozen major nosocomial outbreaks of TB in the United States since 1988. In these outbreaks, more than 200 secondary cases of active disease occurred among patients, of whom as many as 80% to 90% died,1-5 and 30% to 40% of exposed healthcare workers had tuberculin conversion.3-5 This has stimulated intense interest in the problem of nosocomial transmission of TB&9 and a critical reexamination of much of the previously accepted dogma in this area.1o-12 There is no debate regarding the need for isolation of patients with newly diagnosed untreated pulmonary TB. However, once effective therapy has been started for these patients, the duration of contagiousness and need for respiratory isolation remain controversial. In the past, a number of authorities have stated that, once patients begin effective antituberculous therapy, there is no longer a risk of transmission.13-15 Recent statements have been more cautious in this regard.9,16,17 To address the question of contagiousness of patients once effective treatment has begun, the evidence regarding contagiousness of untreated and treated patients with active TB was reviewed. The evidence regarding effect of therapy on contagiousness was categorized as in vitro, animal experimental, and epidemiological. From the Montreal Chest Institute and Respiratory Epidemiology Unit, McGill University, Montreal, Quebec, Canada. Supported by the Fonds de Recherche en Sante de Quebec. The author acknowledges the financial support provided by the Fonds de Recherche en Sante de Quebec and the critical review provided by Dr. Kevin Schwartzman. Address reprint requests to Dr Dick Menzies, Montreal Chest Institute, 3650 St Urbain, Montreal, Quebec 42X 2P4, Canada. 96-RF-031. Menzies D. Effect of treatment on contagiousness of patients with active pulmonary tuberculosis. Infect Control Hosp Epidemiol 1997;18:582-586. This content downloaded from 157.55.39.165 on Thu, 14 Jul 2016 04:36:16 UTC All use subject to http://about.jstor.org/terms Vol. 18 No. 8 READERS' FORUM 583