Falling TB Rates Point to Greater Danger for U.S.

Cheryl Clark, September 29, 2010

A report that may send waves of fear to hospital leaders across the country indicates that infectious disease strides in decimating ordinary tuberculosis cases may in fact position the country for an epidemic rise in multidrug-resistant TB.


Johns Hopkins Bloomberg School of Public Health and Stanford University researchers have created computer simulations that show a paradoxical correlation between falling ordinary TB prevalence rates and an increasing risk for more extensive MDR-TB, infection that is resistant to at least two of the primary antibiotics used for treatment. 

"Since countries with good TB control may be more vulnerable, their self interest dictates greater promotion of case detection and DOTS implementation in countries with poor control to control their risk of MDR-TB," wrote David Bishai, MD, senior author and associate professor in the Bloomberg School's department of Population, Family and Reproductive Health and International Health.

The model is published in the Sept. 22 edition of the journal Proceedings of the Library of Science ONE.

Bishai said that when 75% of active TB cases are detected, improving therapeutic compliance from 50% to 75% can reduce the probability of an epidemic from 45% to 15%.
"But paradoxically, improving the case detection rate from 50% to 75% when compliance with directly-observed-treatment is constant at 75% increases the probability of MDR-TB epidemics from 3% to 45%."

Bishai says that the most successful approach to reduce the risk of multi-drug resistant epidemics "would be to ensure that populations around the world combine high rates of case findings that are tightly coupled to high compliance with directly observed drug therapy."

The World Health Organization estimates that between 500,000 to two million people each year worldwide are infected with MDR-TB, but there were only 111 cases reported in the U.S. in 2006.

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