Tuberculosis relapse due to low weight gain after initial treatment

Among tuberculosis (TB) patients who were underweight when diagnosed, those who subsequently regained less than five percent of their weight during the first two months of treatment had a significantly increased risk of disease relapse, according to results from a large study.

The research appears in the first issue for August 2006 of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.

Awal D. Khan, Ph.D., of the TB Trials Consortium Study Data and Coordinating Center at the Centers for Disease Control and Prevention in Atlanta, and four associates monitored 857 TB patients for two years. Of this group, 61 (7.1 percent) relapsed.

"In a model adjusted for other relapse risk factors, a weight gain of 5 percent or less between diagnosis and completion of a two-month intensive phase therapy among persons underweight at diagnosis was significantly associated with relapse risk," said Dr. Khan.

(For the study, persons were classified as underweight if they were 10 percent below their ideal body weight.)

The authors pointed to an 18.5 percent relapse rate in persons with greater than 5 percent body weight gain and a 50.5 percent relapse rate in persons who gained less than 5 percent in weight.

The researchers said that the association between weight and disease relapse still held among underweight persons who had abnormal chest x-rays and positive sputum cultures after 2 months of anti-tuberculosis treatment.

"Less than 5 percent weight gain could be a marker of increased tuberculosis disease activity and/or poor response to therapy," said Dr. Khan.

TB is a contagious, potentially fatal infection usually caused by the airborne bacterium Mycobacterium tuberculosis. About 85 percent of TB infections are caused by re-activation of dormant bacteria that have been healed and sealed off at the site of the original infection. TB that affects organs other than the lung frequently comes from that site and is spread through the blood.

"The very high relapse rate of 50.5 percent among underweight persons with a cavity on chest radiograph, positive sputum culture after two months of anti-tuberculosis treatment, and five percent or less weight gain during two-month intensive therapy raises the possibility that such patients should receive therapy that is more intensive or of greater duration," said Dr. Khan. "Conversely, the 0.6 percent relapse rate among persons without any of these risk factors suggests that they could possibly receive a shorter duration of therapy."

In an editorial on the research in the same issue of the journal, Wing Wai Yew, M.B., of the Tuberculosis and Chest Unit at Grantham Hospital in Hong Kong, and Chi Chin Leung, M.B., of the Tuberculosis and Chest Service Center for Health Protection at the Department of Health in Hong Kong, wrote: "Indeed, in the study by Drs. Khan and colleagues, only the early weight change, and not the later or total weight change, was found to have an effect among underweight patients, which was independent of cavity or culture status. Such a specific association also suggests something more than purely the effect of nutrition status on the development of the disease. Among persons who might have lost substantial weight because of the illness, effective control of the pathogen in the induction phase is pivotal to the success of the currently employed short-course regimen, and weight gain is likely an independent indicator of clinical response, in addition to culture conversion."

They continued: "Because of resource constraints, the sputum smear alone is the main monitoring tool for treatment progress for TB control programs in developing countries. As body weight has been well-reported to be associated with risk of disease, severity of disease and the response to treatment, it is surprising that little attention has been paid to such a readily measured and inexpensive markerIf such a relationship between body weight and outcomes can be reproduced in large TB programs under diversified service settings, this relatively simple finding could be translated into very significant clinical benefits, especially in resource-limited settings."