Nearly one-third of the world population has latent tuberculosis infection, according to a medical review article by Dr. Suhail Ahmad of Kuwait University. Tuberculosis (TB) is caused by the bacteria Mycobacterium tuberculosis. Only 10 percent or so of people exposed to the bacteria develop active disease. Of the rest, approximately 10 percent are able to clear the pathogen completely. In the remaining cases, tuberculosis bacilli remain in a dormant, non-replicating state. This latent tuberculosis infection can develop into active disease later if the immune system is weakened by immunomodulatory drugs or HIV infection.
Ahmad identified several factors sustaining high global rates of tuberculosis infection:
1. HIV infection, which allows the tuberculosis bacteria to multiply with little resistance from the immune system
2. The emergence of antibiotic-resistant strains of TB
3. Population expansion
4. Low rates of case detection and cure in impoverished countries
5. Diabetes mellitus
6. War, famine, homelessness, and social decay
Latent tuberculosis infection can be detected by the tuberculin skin test (which has a high rate of false positives) and by more specific blood tests which are also more expensive. Treatment options include antibiotic regimens for 2 months to 12 months, depending on the dose and number of drugs.
In the United States, the Advisory Council for the Elimination of Tuberculosis, Centers for Disease Control and Prevention (CDC), set a goal for elimination of tuberculosis by 2010. This goal was not met. In 2010, the number of new active tuberculosis cases reported to the CDC was 11,181. Dr. R. Pratt and colleagues noted that TB disproportionately affects foreign-born persons, African Americans, and Hispanics.
Another group at risk is patients who take tumor necrosis factor (TNF) blockers for inflammatory and autoimmune conditions, according to Dr. J. Harris and Dr. J. Keane of the School of Biochemistry and Immunology, Dublin, Ireland. Rheumatoid arthritis, psoriatic arthritis, Crohn's disease, and ulcerative colitis are commonly treated with these drugs. Harris and Keane recommended that patients who are candidates for TNF blockers should be tested for latent TB and treated if necessary.
References:
1. Ahmad S, “New approaches in the diagnosis and treatment of latent tuberculosis infection”, Respiratory Research 2010; 11: 169. http://www.ncbi.nlm.nih.gov/pubmed/21126375
2. Centers for Disease Control and Prevention, “Trends in tuberculosis – United States, 2010” MMWR Morbidity and Mortality Weekly Report 2011 March 25; 60(11): 333.
http://www.ncbi.nlm.nih.gov/pubmed/21430636
3. Harris J et al, “How tumor necrosis factor blockers interfere with tuberculosis immunity”, Clinical & Experimental Immunology 2010 July 1; 161: 1. http://www.ncbi.nlm.nih.gov/pubmed/20491796
Reviewed August 4, 2011
by Michele Blacksberg R.N.
Edited by Jody Smith
Linda Fugate is a scientist and writer in Austin, Texas. She has a Ph.D. in Physics and an M.S. in Macromolecular Science and Engineering. Her background includes academic and industrial research in materials science. She currently writes song lyrics and health articles.