General measures such as avoiding overcrowded and unsanitary conditions are important aspects of prevention. Hospital emergency rooms and similar locations that are used to treat or house TB patients can be treated with ultraviolet light, which has an antibacterial effect.
Vaccination is one major preventive measure against TB. A vaccine called BCG (Bacillus Calmette-Guérin, named after its French developers) is made from a weakened mycobacterium that infects cattle. Vaccination with BCG does not prevent infection by M. tuberculosis, but it does strengthen the immune system of first-time TB patients. As a result, serious complications are less likely to develop. BCG is used widely in developing countries but is not used in the United States. This is because it protects only 75% of recipients, and because everyone who receives the vaccine reacts positively to future TB screening tests. The problem is identifying the one person in four who has a false negative test result. The effectiveness of vaccination is still being studied. It is not clear whether the vaccine's effectiveness depends on the population in which it is used or on variations in its formulation.
Prophylactic use of isoniazid
Isoniazid can be given for the prevention as well as the treatment of TB. Isoniazid is effective when given daily over a period of six to 12 months to people in high-risk categories. The drug appears to be most beneficial to persons under the age of 25. Because isoniazid carries the risk of side effects (liver inflammation, nerve damage, changes in mood and behavior), it is important to administer the drug only to persons at special risk.
High-risk groups for whom isoniazid prevention may be justified include:
Close contacts of persons with active TB, including health care workers.
Newly infected patients whose skin test has turned positive in the past two years.
Anyone who is HIV-positive with a positive PPD skin test. Isoniazid may be given even if PPD results are negative if there is a risk of exposure to active tuberculosis.
Intravenous drug users, even if they are negative for HIV.
Persons who have never been treated for TB, have positive PPD results, and show evidence of old disease on a chest x ray.
People who have an illness or are taking a drug that can suppress the immune system.
Persons with positive PPD results who have had intestinal surgery, have diabetes or chronic kidney failure, have any type of cancer, or are more than 10% below their ideal body weight.
People from countries with high rates of TB who have positive PPD results.
People from low-income groups with positive skin test results.
Persons with a positive PPD reaction who belong to high-risk ethnic groups (African-Americans, Hispanics, Native Americans, Asians, and Pacific Islanders).
L. Fleming Fallon Jr., MD, PhD, DrPH, The Gale Group Inc., Gale, Detroit,