SAN FRANCISCO -- Extensively drug resistant tuberculosis (XDR-TB) continues to be unearthed around the globe, with implications for U.S. clinicians, researchers said here.
SAN FRANCISCO, May 29 -- Extensively drug resistant tuberculosis (XDR-TB) continues to be unearthed around the globe, with implications for U.S. clinicians, researchers said here.
Just two days after a report at the American Thoracic Society meeting of a rampant XDR-TB problem in India, other investigators said at the same forum that Indian immigrants had already boosted the XDR-TB burden in New York.
"With time we will find it in every country," said Charles L. Daley, M.D., of National Jewish Medical and Research Center in Denver, who presented an overview of the issue to pulmonologists. "We just have to look for it."
As of May 1, the WHO indicated 37 nations with XDR-TB, which it defines as resistance to at least rifampicin and isoniazid from among the first line anti-TB drugs (the definition of MDR TB) in addition to resistance to any fluoroquinolone, and to at least one of three injectable second-line anti-TB drugs used in TB treatment (capreomycin, kanamycin, and amikacin).
India has joined the list, according to Sushil Jain, M.B.B.S., D.N.B., of the Hinduja National Hospital in Mumbai, and colleagues, who revealed a high XDR-TB rate emerging there.
They reviewed all 3,904 TB culture samples received at their tertiary care hospital laboratory in 2005.
Among the 32.25% of TB-positive cultures classified as multidrug resistant, 9.3% (38 samples) were extensively drug resistant.
All cases were in patients with pulmonary TB, and therefore transmissible.
Of the 32 patients who could be followed at one year, 39.47% had died.
India's rate is relatively high, according to a survey of international TB laboratories for 2000 to 2004. The rate Dr. Jain reported was lower than only Eastern Europe and Russia (14%) and South Korea (15%).
The survey, published this year in the journal Emerging Infectious Diseases, found a 6% XDR-TB rate among multidrug resistant cases for industrialized nations and Latin America.
However, in industrialized countries like the U.S., most XDR-TB cases come from foreign-born patients, Dr. Daley noted.
A study in Morbidity and Mortality Weekly Report earlier this year reported that foreign-born persons accounted for 76% of XDR-TB cases in the United States from 2000 to 2006, up from 38% from 1993 to 1999.
Dr. Daley cited data showing that most of the cases in the United States have occurred in New York and California.
In the first characterization of New York's XDR-TB burden, researchers reported here that 60% of cases were among immigrants.
These patients were born in India, China, the Ukraine, El Salvador, South Korea, and Malawi, said Shama D. Ahuja, M.P.H., of the New York City Bureau of Tuberculosis Control, and colleagues.
It is likely that all acquired the infections in their country of origin, because only 57 days had elapsed on average from arrival to diagnosis, they said.
Notably, there were no cases of transmission from these patients.
However, as XDR-TB has been recognized as an entity and given a name only in the past year or two, part of the reason for low rates and relatively few countries with cases is because no one has been looking for it, Dr. Daley said.
According to the 2007 MMWR report, there was sufficient data to rule in XDR-TB for only 50% to 65% of TB cases in the United States, he said.
But, it should have come as little surprise that XDR sprang up now, Dr. Daley said.
With the length of TB transmission and resistance acquisition cycles and the lack of any new TB drugs in the past 40 years, "this is the time that XDR should be hitting us," he said.
Now, "it will be a global effort required to control XDR-TB," Dr. Daley concluded.