Drug-resistant TB poses new threat to HCWs

Strain is 'practically untreatable'

An extensively drug-resistant strain of tuberculosis (XDR-TB) is virtually untreatable and poses a threat to worldwide TB control. Protecting health care workers from this new threat will require vigilant adherence to infection control principles, TB experts say.

Currently, the strain is extremely rare in the United States, representing just 3% of the 1.2% of TB cases that are reported to be multidrug resistant. Yet a recent outbreak in South Africa among HIV-infected individuals revealed its deadly potential: the TB strain killed 52 of 53 infected patients in a single rural hospital.1

XDR-TB is defined as TB that is resistant to isoniazid and rifampicin, the preferred drugs to treat tuberculosis, as well as at least one injectable second-line drug (capreomycin, kanamycin, and amikacin) and one fluoroquinolone.2

"You can just imagine that [if] any health care worker would become infected with one of these extensively drug resistant organisms, there's a very good chance of having a form of TB that's practically untreatable," says Reynard McDonald, MD, medical director of the Global TB Institute at the New Jersey Medical School in Newark.

Only about 10% of those who are TB-infected eventually develop the disease, but the risk is highest for the immunosuppressed, including people who are HIV-positive, transplant patients, or taking steroids.

The infection control precautions used for XDR-TB are the same as for other strains, says Peter Cegielski, MD, MPH, team leader for drug resistant tuberculosis in the international branch of the Division of TB Elimination at the Centers for Disease Control and Prevention in Atlanta.

However, because of the potential risk, "individuals who are particularly susceptible might want to take measures to work in areas where they're less likely to come into contact with TB patients," Cegielski notes.

Health care workers should be educated about the risk of multidrug-resistant TB and XDR-TB and reminded of the importance of rapid TB diagnosis, protective measures, and treatment of latent TB infection, he says.

How would you treat a health care worker with a known exposure to XDR-TB? That would be a troubling question, says McDonald. "If they were involved in the management of someone who clearly had XDR-TB and they converted their skin test after coming into contact with that patient, you [might] think their tuberculin skin test conversion was related to XDR," he says.

"… If they were immunosuppressed, you most certainly would want to try to give them protection, but what in the world would you use? There is no data to guide you about what is appropriate treatment for these individuals," he says.

Meanwhile, public health officials seek better surveillance data on multidrug-resistant TB to help assess and monitor the spread of XDR-TB. "It's critical that health care workers fulfill their responsibility for ensuring that tuberculosis cases are reported properly, including the results of test for suspectibility," says Cegielski. "It appears that the data we have are incomplete."

Overall, tuberculosis in the United States is at its lowest level since reporting began in 1953. In 2005, there were 14,097 cases, or a rate of 4.8 cases per 100,000 people. Multidrug-resistant TB also has declined significantly since CDC and others began combating a resurgence of TB in the early 1990s. However, the decline in TB cases has slowed significantly in recent years.

XDR-TB now has been detected in 27 countries, including Canada, Japan and Norway, and the World Health Organization has convened a Global Task Force on XDR-TB.

"We need to be continue to be vigilant [regarding] tuberculosis in health care settings, both inpatient and outpatient," says Cegielski. "Individuals with prolonged cough — more than two weeks — should be treated as potentially infectious cases."

XDR-TB threatens to derail the public health goal of eliminating tuberculosis in the United States and globally. "Clearly, better drugs and newer drugs are urgently needed," he says.

References

1. Gandhi NR, Moll A, Sturm AW, et al. Extensively drug-resistant tuberculosis as a cause of death in patients coinfected with tuberculosis and HIV in a rural area of South Africa. Lancet 2006; 368:1,575-1,580.

2. Centers for Disease Control and Prevention. Notice to Readers: Revised definition of Extensively Drug-Resistant Tuberculosis. MMWR 2006; 55:1,176.