Variability of Airborne Transmission of Mycobacterium tuberculosis: Implications for Control of Tuberculosis in the HIV Era

Abstract

The recent collision of extensively drugresistant (XDR) tuberculosis with HIV infection in South Africa created an outbreak of tuberculosis with a 98% mortality rate and raised the specter of untreatable tuberculosis. Most of these cases of XDR tuberculosis were probably a result of nosocomial transmission because two-thirds of the patients had been recently hospitalized prior to the onset of tuberculosis and at least 2 health care workers died. A World Health Organization Global Task Force on XDR tuberculosis recommended several interventions including accelerated implementation of infection-control measures to reduce transmission and strategies that promote prevention and control of XDR tuberculosis. In this context the article by Escombe et al. in this issue of Clinical Infectious Diseases could not be more relevant. At first glance it might seem that studies of guinea pigs regarding airborne transmission of pulmonary tuberculosis could offer nothing new. Less than 2 decades after Kochs elegant demonstration of Mycobacterium tuberculosis as the etiologic agent of tuberculosis in 1882 Flugge infected guinea pigs by having patients with tuberculosis cough on them. His logical but erroneous interpretation was that tuberculosis was transmitted by large respiratory droplets. Less than 50 years ago Wells his protege´ Richard Riley and their coinvestigators convinced the world that M. tuberculosis is transmitted by the airborne route. To do so they developed a model of guinea pigs in a penthouse exposed to the air exhausted from an experimental tuberculosis ward which was reproduced by Escombe et al.. When I had the pleasure of meeting Richard Riley several years before his death he thought that his work would probably never be reproduced because of its complexity and expense. Escombe and his team are to be congratulated for proving Riley wrong about this. (excerpt)