Novel Approaches to TB Diagnosis
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Contact Information:

 

Aparna Chhibber 2006 chhibber@stanford.edu

 

Stanford University
Parasites & Pestilence: Infectious Public Health Challenges
Prof. D. Scott Smith, ssmith@stanford.edu


 
 
 


 
 
Tuberculosis: A Global Emergency

Tuberculosis was declared to be a global emergency by the World Health Organization in 1993. WHO estimates that in 2005, roughly nine million people develop active TB, and two million will die. It is estimated that a third of the global population is infected, and about 40 million new infections occur every year. While incidence of TB has declined overall since the 1980s, in many parts of the world, TB rates are on the rise again. Even within the United States, while rates of TB have declined since 1992, 14,000 cases were reported in 2003. About 75% of cases occur in large urban centers. [Cellistis]

Control of TB infection is thus of primary concern around the world and within the United States, especially in metropolitan areas; effective means of detection of TB cases is vital for an effective TB control program. Control programs in the United States (and other low endemic countries) consist primarily of targeted screening of certain sectors of the population, followed by treatment of individuals with active or latent TB infection. In more highly endemic countries, control programs typically examine high risk individuals for active TB followed by treatment. [Pai] Adequate diagnostic techniques are thus required for effective TB control. Current diagnostic techniques widely in use have been employed for over a hundred years. Recently, several new techniques for TB diagnosis have been developed that may significantly improve the efficiency and efficacy of TB control, eventually reducing the disease burden of Tuberculosis in the United States and around the world.

Image from WHO through ReliefWeb: http://www.reliefweb.int/rw/RWB.NSF/db900SID/HMYT-6BKSCZ?OpenDocument
 
M. Tuberculosis Infection
 

M. tuberculosis, a bacterial agent, is spread from person to person by aerosolized droplet infection. The most common site of infection is in the lungs, but many other organs in the body may be susceptibe as well, such as blood, lymph glands, brain, spine, kidneys or other organs. Infections in extrapulmonary sites are not contagious, but can be dangerous for the individual. Roughly 50% of tuberculosis infections are pulmonary. Typical symptoms of pulmonary tuberculosis include fatigue, fever, weight loss, lymphadenopathy, ongoing productive cough, hemoptysis, chest pain; extrapulomnary tuberculosis will produce different symptoms.  

Infection with M. Tuberculosis can result in active infection or latent infection (LMTB). Active infection will be associated with the standard TB signs and symptoms, LTBI is defined as the presence of M. tuberculosis without any symptoms or chest abnormalities. While only active infections are contagious, a portion of latent infections, particularly in individuals at high risk for active TB disease, will become active and thus contagious at some point in an individual's lifetime, and thus control programmes are very concerned with detection of LMTB. Once detected, TB infections are quite curable with strict adherance to a combination drug program including isoniazid (INH), rifampin (RIF), ethambutol, and pyrazinamide. [CDC TB]

Risk factors for the development of active TB disease include:

  • age (young children or elderly)
  • HIV positive or AIDS
  • Close contacts of infected individuals
  • substance abuse
  • diabetes mellitus
  • silicosis
  • cancer of the head or neck
  • leukemia or Hodgkin's disease
  • severe kidney disease
  • low body weight
  • certain medical treatments (such as corticosteroid treatment or organ transplants)
  • specialized treatment for rheumatoid arthritis or Crohn’s disease
    Banner image from Sudan Tribune: www.sudantribune.com/ IMG/arton11330.jpg