Tuberculosis 'Superbug' Not Stateside Threat, Says FP Expert

A dozen cases of so-called totally drug-resistant tuberculosis (TDR-TB) were reported in India in January, but what's considered TDR-TB in India may be treatable elsewhere.

According to the World Health Organization (WHO), the "superbug" cases in India, although severe, do not meet the definition of "totally drug-resistant." Instead, the organization defined this new strain as extensively drug-resistant tuberculosis (XDR-TB).

Family physician Paul Hunter, M.D., who is associate medical director for the City of Milwaukee Health Department, explained that XDR-TB is resistant to at least four of the core anti-TB drugs, the two most powerful of which are isoniazid and rifampicin. This type of TB also may show resistance to any of the fluoroquinolones (e.g., ofloxacin and moxifloxacin) and to any one of three injectable second-line drugs (i.e., amikacin, capreomycin and kanamycin).

"According to the WHO, XDR-TB takes substantially longer to treat than ordinary (drug-susceptible) TB, and requires the use of second-line anti-TB drugs, which are more expensive and have more side effects than the first-line drugs used for drug-susceptible TB," Hunter told AAFP News Now. "TDR basically means you're using everything available at your site and it is ineffective, but that term doesn't mean anything (in this case) because what is available in India is different from what we have available here."

Hunter, who also is an assistant professor of family medicine at the University of Wisconsin, Madison, School of Medicine and Public Health, said that the chances are low that a virtually untreatable form of TB would spread to the United States because immigration regulations require screening for TB infection via skin or blood testing, and people with untreated, active tuberculosis are not permitted to enter the country.

"If someone did slip through the net, that patient would need to be isolated for a significant period of a time and receive complicated regimens of multiple, expensive antibiotics with significant side effects," Hunter said. "This would probably be done at a tuberculosis hospital by experts from one of the four Regional Training and Medical Consultation Centers for tuberculosis."

The bigger issue for stateside physicians, he added, is latent tuberculosis infection (LTBI), which occurs when a person has been exposed to Mycobacterium tuberculosis but does not have symptoms and cannot transmit the bacteria to others. It is only if a person develops active TB that he or she then can spread the disease to others.

"That is where family doctors can really get involved and make the most difference," Hunter said. "FPs are a vital part of the public health response to TB because they can screen high-risk patients with skin and blood testing and follow up positive tests with chest X-rays to rule out active tuberculosis. By following the legal mandates to report known or suspected contagious TB to local health departments, FPs can activate the public health resources needed to prevent transmission of tuberculosis.

"With support from their health systems and local health departments, FPs can efficiently and effectively treat latent TB infection," he added. "FPs can also be crucial in coordinating the care of patients whose active tuberculosis is being managed by other physicians with expertise in treating active TB."

Although only about 10 percent of people with LTBI will develop active TB, some people, such as those with weakened immune systems, are at higher risk of progression to active disease. On Dec. 9, 2011, the CDC released new LTBI treatment recommendations that outline a 12-week combination regimen consisting of isoniazid and rifapentine administered once per week as directly observed therapy (DOT) in patients meeting specific criteria. According to the agency, the new therapeutic regimen "is as effective for preventing TB as other regimens and is more likely to be completed than the U.S. standard regimen of nine months of isoniazid daily without DOT."

Above all, said Hunter, "You have to make sure you don't treat active disease using a single medication or the wrong combination of medications, because that is what leads to drug-resistant TB. If you do it wrong, you're going to push your patients toward drug resistance.

"Don't be a cowboy; follow the national guidelines."