Ever since Andrew Speaker traveled across the Atlantic Ocean with a diagnosed case of tuberculosis (TB) in 2007, the public has been more attuned to the dangers posed by this infectious—and increasingly drug resistant—respiratory disease. Despite generally declining rates of TB in the US, the risks posed by this potentially life-threatening illness are real and significant.
As with many infectious diseases, the worldwide effort to eliminate TB depends upon a robust laboratory infrastructure; TB can only be definitively diagnosed through laboratory testing and only effectively treated after further testing to determine the infecting organism’s susceptibility to available drug therapies.
To commemorate World TB Day, APHL asked two laboratory experts to share their thoughts about the greatest laboratory achievements and challenges with regard to this ancient, evolving scourge. Here’s what they had to say.
Dave Warshauer, PhD, D(ABMM)
Deputy Director, Communicable Diseases
Wisconsin State Laboratory of Hygiene
Ed Desmond, PhD, D(ABMM)
Chief, Mycobacteriology and Mycology Section
Microbial Diseases Laboratory
Center for Infectious Diseases
California Department of Public Health
TB Laboratory Achievements
The traditional method of confirming a case of TB requires several weeks to grow or culture colonies of the rod-shaped TB bacterium, Mycobacterium tuberculosis, in the laboratory. Both of our experts pointed to the development of same-day, DNA-based testing methods—referred to as nucleic acid amplification testing or NAAT—as a “huge” milestone.
Genotyping—recording the genome of different strains of TB—is another important advance.
Previously, acid-fast smear negative patients [those whose specimens tested negative by a less sensitive preliminary test] were often not started on anti-TB medications until the culture became positive and Mycobacterium tuberculosis was isolated several weeks later. Now, more sensitive NAAT methods have led to earlier detection of many TB patients, who are put on treatment sooner. This promotes quicker resolution of the disease for these patients, and reduces the amount of time they are infectious to others.
Another impact of NAAT stems from its ability to predict drug resistance. When NAAT detects M. tuberculosis DNA and mutations associated with drug resistance, the patient can be put on a treatment regimen that is suitable for drug-resistant TB. Studies have shown that this reduces the amount of time that these patients, who may be shedding drug-resistant bacteria, are infectious.
I might add to the list of achievements the contribution of genotyping to tuberculosis control. Over the past ten years, the Centers for Disease Control and Prevention has built up a genotyping laboratory system that now genotypes the cultures from about 80% of culture-positive TB patients. This has enabled TB control programs to discover unsuspected outbreaks and break new ground in finding out where and in what circumstances TB is spread in the population.
TB Laboratory Challenges
TB is such a global problem. We talk about elimination of TB in the United States, but to do that you’ve got to attack the problem globally. We’re not going to eliminate TB even in the US unless we can intervene in the rest of the world, since more than half US cases are in the foreign-born.
Continued support of our public health infrastructure in the United States is a major challenge. For many years now we’ve had level funding for TB, which is a decrease in light of inflation. People can’t always see the value of prevention.
In California, about 75% of TB cases are in the foreign-born. This means that we in public health face a continuing challenge for the control of tuberculosis. In February, 2009, CDC published a plan to combat extensively drug resistant TB in the United States. The CDC task force that developed the plan made several recommendations calling for collaboration to develop TB laboratory capacity in foreign, high-burden countries. These recommendations require the participation of laboratory staff.
The same CDC plan lists as objective 1.1, at the top of the list: “increase awareness of the need to develop necessary capacity and capabilities for the laboratory diagnosis of TB.” TB laboratory capabilities must be developed and not just maintained in order to control the increasing threat of drug-resistant tuberculosis.
It’s important to remember that allowing the public health laboratory infrastructure to deteriorate could lead to public health threats such as increased incidence of tuberculosis. Identifying sufficient resources to sustain and develop public health laboratories is a significant challenge.