Archive for May 4th, 2011
Wednesday, May 4th, 2011
Productive cough, shortness of breath, and fever are symptoms of tuberculosis and pneumonia caused by certain common types of bacteria; these symptoms may also be caused by PCP, certain viruses, Kaposi’s sarcoma in the lung, and several other unusual conditions.
Tuberculosis (TB)-The most common symptoms of TB are cough, bloody sputum, shortness of breath, fever, weight loss, chest pain with breathing, and night sweats. As with PCP, the tempo of tuberculosis is generally slow, usually progressing over a period of weeks or months. During this time the person is usually fatigued, has night sweats, and loses weight. TB can occur in the lung, but it can spread to almost any part of the body. People with HIV infection often have TB relatively early in the course of the infection, when the CD4 count is fairly high: TB
apparently has enough clout that it does not require a severely weakened immune system to cause disease.
TB, which is caused by a bacterium called Mycobacterium tuberculosis, can be active or inactive. When it is active, the bacterium is reproducing and the person has symptoms of TB. When it is inactive, Mycobacterium tuberculosis is dormant in the lung, much the way
Pneumocystis carinii is dormant in the lung. People with inactive TB have no symptoms, and all cultures for Mycobacterium tuberculosis are negative.
The only way to find out whether a person has been infected with Mycobacterium tuberculosis is the skin test most people are familiar with, done on the forearm. The skin test is a shallow injection of a protein called a purified protein derivative, or PPD, made from Mycobacterium tuberculosis. If the area around the injection become red and thickened two or three days later, the person’s immune system has already responded to the bacterium. In other words, a positive skin test means that Mycobacterium tuberculosis is in the body and the person has TB, either active or inactive. The only other evidence of infection might be a chest x-ray showing the scars of previous infections with TB that the person may be unaware of. Most, though not all, people with active TB have had inactive TB for several years previously.
If the skin test is positive, it is followed by sputum tests for TB and x-rays. If the sputum test is also positive, if symptoms are ascribed to TB, or if the x-ray shows new changes, the person has active TB. Otherwise, the TB is inactive.
It is especially important for people with HIV infection to have a skin test. Inactive TB can be treated with a drug, isoniazid (INH), that will prevent active TB. Active TB is treated more aggressively, with three or more drugs.
Mycobacterium tuberculosis must be distinguished from a related microbe called Mycobacterium avium-intracellulare, or MAI. MAI causes infections in many organs throughout the body. This distinction between Mycobacterium tuberculosis and MAI is important, not only for deciding what the treatment should be, but also for preventing transmission. Mycobacterium tuberculosis, the only contagious mycobacterial infection, can be transmitted from one person to another by close contact over a period of several months. For this reason, the people most likely to be infected are those who live with the infected person. But an infected person who has been treated with drugs against TB for several days is unlikely to transmit the infection to others. This means that once treatment has started, the likelihood that it will be spread to others is reduced or nil. The standard recommendation for testing those people who have been exposed to TB for long periods is to do the skin test, and if it is positive, to follow it with chest x-rays.