By Dr Ananya Mandal, MD

The U.S. Centers for Disease Control and Prevention (CDC) has released new guidelines on treating so-called “latent” tuberculosis (TB) infection in the United States. They suggest the course of the therapy from about 9 months could be shortened to 3 months.

Experts say latent TB infection occurs when a person is infected with TB bacteria but does not yet have symptoms and so cannot transmit the bacteria to others. However, if the bacteria become active, the person will develop the disease and can also spread it to others. Certain people, including those with weakened immune systems, are more likely to progress from latent to active TB.

“This regimen has the potential to be a game-changer in the United States when it comes to fighting TB,” said CDC Director Thomas Frieden said in a CDC news release. “It gives us a new, effective option that will reduce by two-thirds - from nine months to three months - the length of time someone needs to take medicine to prevent latent TB infection from progressing to active TB disease.”

The CDC report adds that many high-risk people with latent TB feel fine and don't begin the nine-month course of treatment, which typically requires 270 daily doses of the anti-TB drug isoniazid. And many of those who do begin the therapy don't see it through to the end. However, the new regimen streamlines the treatment to 12 once-per-week doses of isoniazid, along with another anti-TB drug called rifapentine.

The regimen is recommended for otherwise healthy people ages 12 and older who are at high risk for developing TB disease. This includes anyone who has had recent exposure to contagious TB, conversion from negative to positive on a test for TB infection or a chest X-ray indicating prior TB disease. People living with HIV who are otherwise healthy and not taking antiretrovirals may also use this regimen if TB preventive treatment is indicated.

Because the safety of the regimen for some patients is unknown, it is not recommended for use among children under age 2, women who are pregnant or planning to become pregnant, and HIV-infected people taking antiretrovirals. Patients whose TB infection is presumed to be the result of exposure to a person with TB disease that is resistant to one of the two drugs should not receive this regimen.

Monitoring for adverse events is critical. Healthcare workers supervising patients who are taking the drugs should educate patients and monitor for possible adverse effects, and report any problems to a clinician. Patients should undergo a clinical assessment at least monthly.

The new guidelines were published in the Dec. 9 issue of the CDC's Morbidity and Mortality Weekly Report.

“If we are going to achieve our goal of TB elimination in the United States, we must ensure that those with latent TB infection receive appropriate evaluation and treatment to prevent their infection from progressing to TB disease and possibly spreading to others,” Dr. Kevin Fenton, director of CDC's National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, said in the news release. “It is critical that we accelerate progress against TB in the United States in order to avoid a resurgence of the disease,” he added.

These new guidelines apply only to the United States, CDC officials said. Further research is likely needed before this regimen could be recommended for countries with a high incidence of TB, particularly those that have high rates of HIV and where there's a greater risk of TB re-infection.

The number of U.S. cases of active TB disease fell to an all-time low of 11,182 in 2010. But about 4 percent of the U.S. population, or 11 million people, have latent infections. TB continues to disproportionately affect people of color and foreign-born persons in this country.

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