Virulent Drug-Resistant TB Strain Emerges

A “virtually untreatable” form of tuberculosis -- resistant to at least five classes of antibiotics -- is quickly emerging across the globe, according to a federal report released Thursday.

The total number of infections by the new strain is still relatively small, but researchers fear that it will spread rapidly in the TB incubators of Eastern Europe, India and China.

In 2004, the strain accounted for 11% of drug-resistant TB cases in industrialized countries, up from 3% in 2000.

“The time to act is now to prevent a new pandemic,” said Dr. Marcos Espinal, executive secretary of the World Health Organization’s Stop TB Partnership.

The data on the new TB strain, published in the U.S. Centers for Disease Control and Prevention’s Mortality and Morbidity Weekly Report, come at a time when the prevalence of TB in the United States has reached its lowest point since record-keeping began in 1953 -- 4.8 cases per 100,000.

That translates to 14,516 cases in 2005, a 3.8% decline from the previous year, according to a second study in the report.

Even that good news has its dark side, says Dr. Kenneth G. Castro, assistant surgeon general and director of the CDC’s Division of Tuberculosis Elimination.

“This decrease is one of the smallest declines in more than a decade,” suggesting that efforts to control the infection have reached a plateau, he said Thursday in a telephone conference.

Tuberculosis rates declined 3% in California to a historic low of 2,900 cases in 2005, according to Dr. Mark Horton, the state public health officer.

The rate in California was 7.9 cases per 100,000 people, nearly double the national rate, with more than 75% of the cases occurring in people born in other countries.

Los Angeles County had the highest number of cases, 906. San Diego County had 320, Orange County 224 and Riverside County 75. Two hundred Californians died last year of TB.

The evolution of drugresistant strains of Mycobacterium tuberculosis is a result of TB patients failing to complete the six-month course of therapy and of physicians failing to prescribe the proper therapy, Castro said.

The so-called multidrugresistant strains began appearing in the early 1980s. The term refers to bacteria that are resistant to the two first-line therapies normally used to treat the disease, the antibiotics isoniazid and rifampin.

“We let our guard down” with the emergence of multidrug-resistant strains “and we paid dearly for it,” Espinal said.

The new strain, which researchers call “extensively drug-resistant TB,” is resistant not only to those two drugs, but to at least three of the six classes of drugs used for second-tier therapy -- aminoglycosides, polypeptides, fluoroquinolones, thioamides, cycloserine and para-aminosalicylic acid.

Physicians use those drugs to treat multidrug-resistant cases, but the drugs’ use is worrisome because they are more toxic, more expensive and less effective. A course of therapy for multidrug-resistant TB may require two years instead of six months and may even involve surgery to remove severely affected parts of the lung.

Treating patients with extensively drug-resistant TB is even more difficult.

The normal death rate for patients with TB is about 5% to 6%, and fatalities occur mostly among patients who wait too long to seek therapy. The mortality rate is about 20% among those with multidrug-resistant TB and at least 33% among those with extensively drugresistant TB, Castro said.

Worldwide, about 9 million people become ill with tuberculosis each year and 1.7 million die of it.