are excerpts from the article, which was published recently in the open access
year, more than nine million people develop tuberculosis -- a contagious infection
usually of the lungs -- and nearly two million people die from the disease. Tuberculosis
is caused by Mycobacterium tuberculosis. These bacteria are spread in airborne
droplets when people with the disease cough or sneeze."
people infected with M. tuberculosis never become ill -- their immune system
contains the infection. However, the bacteria remain dormant within the body and
can cause tuberculosis years later if host immunity declines. The symptoms of
tuberculosis include a persistent cough, weight loss, and night sweats. Diagnostic
tests for the disease include chest X-rays, the tuberculin skin test, and sputum
cultures (in which bacteriologists try to grow M. tuberculosis from mucus
brought up from the lungs by coughing). Tuberculosis can usually be cured by taking
several powerful antibiotics daily for several months."
have found that a minority of patients actually transmit tuberculosis, that the
infectiousness of transmitters varies greatly, and that effective antibiotic treatment
decreases infectiousness. Since the 1950s, however, multidrug-resistant (MDR)
and more recently extensively drug-resistant (XDR) strains of M. tuberculosis
have become widespread."
of drug-resistant tuberculosis is much more difficult than normal tuberculosis,
requiring even more antibiotics, and for long periods, up to 2 years and beyond.
In addition, HIV weakens the immune system and as a result, HIV-positive people
are much more likely to develop active tuberculosis (and to die from the disease,
which also speeds the development of HIV/AIDS)
than people with a healthy immune system."
these changes altered tuberculosis transmission between people? The answer to
this question might help to optimize the control of tuberculosis infection, particularly
in hospitals. In this study, the researchers investigated current patterns of
tuberculosis infectiousness among HIV-positive patients by recreating the 1950s
guinea pig model for tuberculosis transmission."
the 505 study days, although 97 HIV-positive patients with tuberculosis were admitted
to the ward, just ten patients were responsible for virtually all the characterized
cases of tuberculosis among the guinea pigs. Six of these patients had MDR tuberculosis
that had been suboptimally treated. The average patient infectiousness over the
entire study period was 8.2 quanta per hour-six times greater than the average
infectiousness recorded in the 1950s. Finally, the three most infectious patients
(all of whom had suboptimally treated MDR tuberculosis) produced 226, 52, and
40 quanta per hour."
findings show that a few inadequately treated HIV-positive patients with MDR tuberculosis
caused nearly all the tuberculosis transmission to guinea pigs during this study.
They also show for the first time that tuberculosis infectiousness among HIV-positive
patients is very variable. The increase in the average patient infectiousness
in this study compared to that seen in the 1950s hints at the possibility that
HIV infection might increase tuberculosis infectiousness. However, studies that
directly compare the tuberculosis infectiousness of HIV-positive and HIV-negative
patients are needed to test this possibility."
importantly, this study demonstrates the potentially high infectiousness of inadequately
treated MDR TB patients and their importance in ongoing TB transmission. These
findings suggest that rapid, routine testing of antibiotic susceptibility should
improve tuberculosis control by ensuring that patients with MDR TB are identified
and treated effectively and quickly."
the study authors re-emphasized the importance of implementing environmental control
measures (for example, adequate natural or mechanical ventilation of tuberculosis
wards, crowded waiting rooms, or emergency departments where tuberculosis patients
may be found) to prevent airborne tuberculosis transmission in health-care facilities,
particularly in areas where many patients are HIV positive and/or where MDR tuberculosis
Escombe, DA Moore, RH Gilman, and others. The Infectiousness of Tuberculosis Patients
Coinfected with HIV. PLoS Medicine 5(9): e188. September 2008. (Free