TB

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Tuberculosis (TB) is an ancient disease that was relatively uncommon here in the U.S until the 1980s. Despite the fact that it was rare, there were some famous historical figures, for example Doc Holliday, who suffered from it. It gave rise to sanitariums in the late nineteenth and early twentieth century as it was thought that fresh air, rather than the highly polluted air then present in cities, would help cure it. There was no treatment for it until the advent of antibiotics in the mid twentieth century. Because those who had it lost a great deal of weight, it was called consumption.

TB is an urban disease and is spread much the same way as coronavirus, that is by droplets spewed into the air by coughing. However, TB is difficult to catch and usually requires multiple or prolonged contacts with an infected person. In most healthy people, should they catch TB, their immune system can keep it in check for years, if not decades. This is called latent TB. People with latent TB have no symptoms.

TB is caused by a bacterium called Mycobacterium tuberculosis, or M tuberculosis. A related bacterium, M leprae, causes leprosy. In the 1980s, with the advent of HIV/AIDS, a virulent, highly resistant strain of TB called M avium intracellularae, made its appearance in these individuals who had severely compromised immune systems due to AIDs. Mycobacteria have hardy, strong cell walls which makes them very resistant to many antibiotics. In addition, they grow very slowly in culture media. In a culture, it takes M tuberculosis about 20 days for one cell division cycle. For comparison, it takes E coli about 20 minutes.

As noted above, TB infection without symptoms is called latent TB. Worldwide, there are about 2 billion individuals with latent TB. A skin test called a PPD test, where a fluid containing protein (Purified Protein Derivative) from M tuberculosis is injected under the skin, can detect latent TB. Because the immune system of someone with latent TB has been activated, there will be redness and swelling at the injection site. Because treatments like chemotherapy, steroids, and anti-rejection medications following an organ transplant can weaken the immune system and convert latent TB into active TB, a PPD test to detect latent TB will be given before starting treatment. BCG (bacillus Calmette Guerin), a TB vaccine, can cause a false-positive PPD. It is used in Europe and most of the world, but not here in the U.S. because it can cause a positive PPD and is ineffective when given to adults.

The symptoms of active TB include cough for more than three weeks, hemoptysis (coughing up blood), chest pain with breathing and coughing, weight loss, fatigue, night sweats, fever, chills, and loss of appetite. Active TB causes pneumonia, which can be heard with a stethoscope and seen on chest X ray. TB can spread outside the lungs to the spine, kidneys, and brain. Because of its strong cell wall and slow growth rate, TB is difficult to treat and treatment can last well over a year. Treatment includes antibioticssuch as isoniazid (INH), rifampin, ethambutol, and pyrazinamide. The CDC recommends that those at risk for latent TB, namely those with HIV/AIDS, IV drug addicts, those in contact with an infected person, those who work in prisons and healthcare facilities, and those from areas where TB is common (Latin America, Africa, and Asia), should be screened with a PPD.

For more information go to: www.cdc.gov/tb 

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By Peter Galvin, MD

 

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