TUESDAY, Jan. 27 (HealthDay News) -- The almost 20 percent of tuberculosis patients in the United States who say they abuse alcohol or illicit drugs are more contagious and difficult to treat than other TB patients, a new study shows.

Researchers analyzed data from 153,268 patients aged 15 or older. Of those patients, 28,650 (18.7 percent) reported substance abuse. That's a greater percentage than any other established risk factor for TB, including recent immigration to the United States (12.9 percent), HIV infection (9.5 percent), living in a group setting (6.6 percent), homelessness (6.3 percent), or working in a high-risk job (4.3 percent).

Among TB patients not infected with HIV, those who reported substance abuse were 1.8 times more likely to have a more contagious form of TB. Among women with TB, substance abusers were 2.4 times more likely to experience treatment failure.

The findings were published in the Jan. 26 issue of the Archives of Internal Medicine.

"Our results suggest that substance abuse is the most commonly reported modifiable behavior impeding TB elimination efforts in the United States," John E. Oeltmann, of the U.S. Centers for Disease Control and Prevention, and colleagues, wrote in a news release from the journal.

"The relation between substance abuse and increased transmission of (TB) can be explained in several ways, some of which are indirect and revolve around delayed diagnosis and difficulties identifying at-risk contacts, screening them for TB and treating patients with positive findings," the researchers noted. "Persons who abuse substances may have less access to routine medical care, potentially leading to delayed diagnoses. As the disease progresses, patients tend to become more contagious."

The study authors also said substance abusers are less likely to be screened for TB or to begin or complete TB treatment, problems compounded by the fact that substance abusers have weakened immune systems. In addition, TB medications are usually metabolized by the liver, which can be damaged by substance abuse.

"Tuberculosis control and substance abuse programs need to work together to simultaneously treat the diseases of addiction and TB," the researchers concluded.

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