The latest national surveillance data show that tuberculosis (TB) rates reached an all-time low in the United States in 2005, but progress to eliminate TB is slowing.(1) Furthermore, the increasing occurrence of drug-resistant TB, including extensively drug-resistant cases, presents significant challenges to treatment and control of the disease both in the United States and abroad.
A total of 14,093 TB cases were reported in the United States in 2005, down from 14,516 cases in 2004. The 2005 national TB case rate 4.8 cases per 100,000 persons was the lowest since reporting began in 1953. However, the decline of 3.8 percent in the national TB case rate from 2004 to 2005 was one of the smallest declines in more than a decade.
At the same time, persons with multi-drug-resistant (MDR) TB TB that is resistant to at least two first-line therapies (isoniazid and rifampin) -- increased 13.3 percent in the United States from 2003 to 2004, the most recent years for which those data are available. This was the largest single-year increase in MDR TB since 1993.
MDR TB, which is difficult and costly to treat, and can be fatal, now accounts for 1.2 percent of all TB cases for which drug-susceptibility data are available. Closely following MDR TB trends in the coming years will be critical in determining whether the 2005 increase represents a nationwide trend, and in understanding the implications of resistance for TB treatment and control.
Other new CDC research reports for the first time on the worldwide emergence of extensively drug-resistant (XDR) TB or TB that is resistant to at least two main first-line drugs and additionally to three or more of the six classes of second-line drugs.(2) From 2000 to 2004, 2 percent of TB patients whose isolates were tested in a survey of a worldwide laboratory network were classified as XDR TB. Over the five-year period in this survey, XDR TB increased from 5 percent of MDR TB cases in 2000 to 6.5 percent in 2004 (excluding South Korea). In the industrialized nations in this survey (including the United States), XDR TB increased from 3 percent of MDR TB cases in 2000 to 11 percent in 2004.
The emergence of XDR TB is cause for concern because it is widely distributed geographically, including in the United States, and renders patients virtually untreatable with available drugs.
Importantly, the emergence of MDR TB 15 years ago was a harbinger of a pandemic; this scenario must be prevented from happening with XDR TB.
TB is a serious threat both in the United States and abroad. Globally, more than one-third of the worlds population is infected with the bacteria that cause TB, and each year approximately 9 million people become ill with the disease, and 2 million of those die. The ability of the disease to develop resistance to treatments and to travel easily across borders makes worldwide TB control efforts critical.
The CDC is working with partners around the world to ensure that adequate resources and tools are in place to prevent further drug resistance. These efforts include strengthening national TB programs and health care professionals to diagnose and ensure completion of TB treatment, developing global policy recommendations, improving standards for second-line drug testing, designing new treatment regimens, and improving tests to diagnose the disease. The CDCs global efforts also include working with officials in Mexico and other countries to improve TB control on the U.S. borders, improving overseas screening for immigrants and refugees and providing diagnoses and care to recent arrivals from countries that have a high incidence of TB.
1. CDC. Trends in Tuberculosis United States, 2005. MMWR;55(10):TK-TK.
2. CDC. Worldwide emergence of Mycobacterium tuberculosis with extensive resistance to second-line drugs. MMWR;55(10):TK-TK.