Tuberculosis, Respiratory

Risk: TB is more common in men and blacks. Miliary TB mostly affects patients aged 65 years and older (Lessnau). Native Americans are more likely to develop TB. TB and lung cancer have been identified as comorbid diagnoses in 5% of cases, but whether having TB alone increases the risk of cancer has not been clearly documented (Agrawal).

Since 1985, however, the number of TB cases has increased. Reasons for this increase include the HIV/AIDS epidemic, increased numbers of immigrants from countries where TB is prevalent, increased poverty, illicit drug use, poor compliance with treatment programs, and more individuals residing in nursing homes.

Incidence and Prevalence: Roughly 15 million patients have TB in the US; annually less than 0.1% of patients have cavitary smears that are positive for TB (Agrawal). Approximately 10% of all infected patients are likely to develop reactivation of TB with the highest risk of doing so occurring within the first 2 years of primary infection (Agrawal). At one time, TB was the leading cause of death in the US, but improvements in hygiene, nutrition, and medical care during the early part of the twentieth century dramatically reduced the incidence of TB. Worldwide 1.5% of TB patients have the miliary form (Lessnau). In other parts of the world, 19% to 43% of people have TB with or without any symptoms with an annual incidence rate of roughly 4% (Agrawal).

History: Individuals with early symptoms may report fatigue, weight loss, fever, night sweats, and loss of appetite. As the disease progresses, there may be chest pain with a productive cough. Sputum also increases and may eventually be streaked with blood (hemoptysis). Shortness of breath may indicate damage in the lungs.

Physical exam: Individuals with TB are often chronically ill, but may present with only minimal signs and symptoms. Chest sounds may be abnormal, especially over the upper lobes of the lungs. Weight loss and muscle wasting ("consumption") may be present.

Tests: A tuberculin skin test (Mantoux test) is used to identify individuals infected with the TB bacteria 6 to 8 weeks after exposure. A positive test, however, does not indicate that the individual has active TB, only that there has been an infection by the bacteria sometime in the past. Because this test can report false negative with a recent infection (less than 2 to 3 months previously) or in immunocompromised individuals (HIV), it should be repeated if a person has recent exposure to TB. Once the individual has had a positive skin test, further skin testing is not recommended due to skin damage at the reaction site. Those with a positive skin test should be tested by chest x-ray.

An x-ray identifies the characteristic lesions in the lungs and may also reveal fluid in the pleural space (pleural effusion) or an enlarged heart (pericarditis). An x-ray of the kidneys using injected dye outlines the kidneys, revealing abnormal masses or cavities that may be caused by TB. A chest CT is a better test than a chest x-ray and has increased sensitivity and specificity. Ultrasound can be helpful in imaging the liver. Head CT and MRI can reveal lesions in the brain that are infected with TB.

To confirm the diagnosis, a culture is used to identify the TB bacteria. Material for culture may include a sample of material expelled from the lungs (sputum), infected fluid drawn from the chest, abdomen, joint, or around the heart, or a small piece of infected tissue (biopsy). Because TB bacteria grow very slowly, this culture can take up to 4 weeks. Cultures are also used in sensitivity tests to determine what drugs will best combat the bacteria. A polymerase chain reaction (PCR) may be performed on a sample of spinal cord fluid to identify tuberculous meningitis. Tuberculosis of the female reproductive organs may be identified through examination of the pelvis using a laparoscope or from scrapings inside the uterus.

Newer and more rapid DNA tests are beginning to be used for diagnosis. These tests use techniques that amplify the tuberculosis bacterial DNA and can speed the time for diagnosis to 2 days.

Individuals with TB should also be tested for HIV infection since TB often occurs early in the course of HIV infection. People who have come into close contact with the patient, such as spouse and family members, need tuberculin skin testing. If their close contacts have a positive skin test, a chest x-ray is indicated to rule out the spread of disease to the lungs.