Patients with drug-resistant TB may account for high proportion of new infections

Study reveals that inadequate treatment can leave people highly infectious<em> - News Release </em>

Issued by PLoS Medicine
Tuesday 16 September 2008

Inadequate treatment of antibiotic-resistant tuberculosis (TB) can leave patients highly infectious, and small numbers of such patients may drive transmission of the disease in the very health care facilities intended to treat it, according to research published in PLoS Medicine.

Every year, more than nine million people develop tuberculosis — a contagious infection usually involving the lungs — and nearly two million people die from the disease. The bacteria that cause TB are spread in airborne droplets when people with the disease cough or sneeze.

Adapting a detection system used in classic 1950s experiments, Rod Escombe of Imperial College London, and colleagues in Perú and the UK investigated airborne infectious tuberculosis in a hospital in Lima. By venting air from an HIV-tuberculosis ward through a guinea-pig enclosure on the hospital roof, and genetically matching the strains of TB infecting the guinea pigs to those cultured from patients, the investigators were able to determine which patients and strains accounted for most of the guinea pig infections.

They found that only 8.5 percent of the 118 admissions to the HIV-TB ward during the 505-day study accounted for 98 percent of the guinea pig TB infections. Ninety percent of the infections were traced to patients with TB that was resistant to multiple antibiotics, and a small number of such patients were found to have coughed out very high numbers of infectious bacteria.

This study demonstrates the potentially high infectiousness of inadequately treated patients with multiply drug-resistant tuberculosis (MDR-TB) and HIV infection, and suggests that rapid, routine testing for antibiotic susceptibility should improve TB control by ensuring that patients with drug-resistant TB are identified and treated effectively and quickly.

The bacteria that cause TB are spread in airborne droplets when people with the disease cough or sneeze.

The results also confirm the importance of implementing TB infection control measures (for example, provision of isolation rooms, and adequate natural or mechanical ventilation of tuberculosis wards, crowded waiting rooms or emergency departments where tuberculosis patients may be found) to prevent airborne TB transmission in health-care facilities, particularly in areas where many patients are HIV positive and/or where MDR-TB is common.

Dr Rod Escombe, from the Department of Infectious Diseases and Immunity at Imperial College London and one of the authors of the study, said: "We need to identify which patients have drug-resistant TB as soon as possible, so that we can treat them promptly with the correct medicines and prevent them from spreading infection. In many developing countries, the diagnosis of drug resistant TB is often only made once drugs have failed, but by this late stage the patients can potentially have infected countless other people.

Our study also suggests that some of the waiting rooms and clinics which have been set up to help TB and HIV patients might be inadvertently facilitating the spread of drug-resistant TB, because of the way they are designed. It is crucial that the spaces where patients congregate aren’t overly crowded and poorly ventilated, and that there is a lot of fresh air circulating around the room. This way, if someone who's infected with drug-resistant TB coughs, we can minimise the chances of healthy staff or visitors becoming infected , or patients with normal TB acquiring drug resistant disease."

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Paper information: Escombe AR, Moore DAJ, Gilman RH, Pan W, Navincopa M, et al. (2008) "The infectiousness of tuberculosis patients coinfected with HIV." PLoS Med 5(9): e188. doi:10.1371/journal.pmed.0050188