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Pulmonary tuberculosis

Definition

Pulmonary tuberculosis (TB) is a contagious bacterial infection caused by Mycobacterium tuberculosis (M. tuberculosis). The lungs are primarily involved, but the infection can spread to other organs.

Causes, incidence, and risk factors

Tuberculosis can develop after inhaling droplets sprayed into the air from a cough or sneeze by someone infected with M. tuberculosis. The disease is characterized by the development of granulomas (granular tumors) in the infected tissues.

The usual site of the disease is the lungs, but other organs may be involved. The primary stage of the infection is usually asymptomatic (without symptoms). In the United States, the majority of people will recover from primary TB infection without further evidence of the disease.

Primary pulmonary TB develops in the minority of people whose immune systems do not successfully contain the primary infection. In this case, the disease may occur within weeks after the primary infection. TB may also lie dormant for years and reappear after the initial infection is contained.

Infants, the elderly, and individuals who are immunocompromised -- for example, those with AIDS, those undergoing chemotherapy, or transplant recipients taking antirejection medications -- are at higher risk for progression to disease or reactivation of dormant disease. In pulmonary TB, the extent of the disease can vary from minimal to massive involvement. Without effective therapy, the disease becomes progressively worse.

The risk of contracting TB increases with the frequency of contact with people who have the disease, with crowded or unsanitary living conditions and with poor nutrition. Recently, there has been an increase in cases of TB in the U.S. Factors that may contribute to the increase in tuberculous infection in a population are:

Increase in HIV infection
Increase in number of homeless individuals (poor environment and poor nutrition)
The appearance of drug-resistant strains of TB

Incomplete treatment of TB infections (such as failure to take medications for the prescribed length of time) can contribute to the emergence of drug-resistant strains of bacteria.

Individuals with immune systems damaged by AIDS have a higher risk of developing active tuberculosis -- either from new exposure to TB or reactivation of dormant mycobacteria. In addition, without the aid of an active immune system, treatment is more difficult and the disease is more resistant to therapy.

In the U.S., there are 10 cases of TB per 100,000 people, but it varies dramatically by area of residence and socio-economic class. Also see:

Disseminated tuberculosis (affects the whole body)
Atypical mycobacterial infection

Symptoms

Limited to minor cough and mild fever, if apparent
Fatigue
Unintentional weight loss
Coughing up blood
Fever and night sweats
Phlegm-producing cough

Additional symptoms that may be associated with this disease:

Wheezing
Excessive sweating, especially at night
Chest pain
Breathing difficulty

Signs and tests

Examination of the lungs by stethoscope can reveal crackles (unusual breath sounds). Enlarged or tender lymph nodes may be present in the neck or other areas. Fluid may be detectable around a lung. Clubbing of the fingers or toes may be present.

Tests may include:

Chest x-ray
Sputum cultures
Tuberculin skin test
Bronchoscopy
Thoracentesis
Chest CT
Interferon (IFN)-gamma blood test. This type of test looks for an immune response to proteins produced by M. tuberculosis. In December 2004, the FDA approved the QuantiFERON-TB Gold (QFT-Gold) test as an alternate to the traditional tuberculin skin test (TST).
Rarely, biopsy of the affected tissue (typically lungs, pleura, or lymph nodes)

Treatment

The goal of treatment is to cure the infection with antitubercular drugs. Daily oral doses of multiple drugs -- which may include combinations of rifampin, isoniazid, pyrazinamide, ethambutol, or occasionally others -- are continued until culture results show the drug sensitivity of the mycobacterial infection. This helps to guide the selection of drug therapy.

Treatment is typically continued for 6 months, but longer courses may be required for AIDS patients or those whose disease responds slowly. For atypical tuberculosis infections, or drug-resistant strains, other drugs and different lengths of therapy may be indicated to treat the infection.

Hospitalization may be indicated to prevent the spread of the disease to others until the contagious period has been resolved with drug therapy. Normal activity can be continued after the contagious period.

Support Groups

The stress of illness may be helped by joining a support group where members share common experiences and problems. See lung disease - support group.

Expectations (prognosis)

Symptoms may improve in 2 to 3 weeks. A chest x-ray will not show this improvement until later. Prognosis is excellent if pulmonary TB is diagnosed early and treatment is begun.

Complications

Pulmonary TB can cause permanent lung damage if not treated early.

All medications used to treat TB have some toxicity. Rifampin and isoniazid may both cause a non-infectious hepatitis. Rifampin may also cause an orange or brown coloration of tears and urine.

Those taking ethambutol should have their vision monitored, as this drug sometimes affects the eye. Any rash, abdominal pain, jaundice, or tingling in toes or fingers may be a sign of drug toxicity and should be reported to your doctor immediately.

Other complications include drug resistance to particular TB strains and a relapse of the disease in some patients.

Calling your health care provider

Call your health care provider if you have been exposed to tuberculosis, or if symptoms of TB develop.

Call your health care provider if symptoms persist despite treatment.

Also call if new symptoms develop, including indications that complications are developing.

Prevention

TB is a preventable disease, even in those who have been exposed to an infected person. Skin testing (PPD) for TB is used in high risk populations or in individuals who may have been exposed to TB, such as health care workers.

A positive skin test indicates prior TB exposure. Preventive therapy should be discussed with your doctor. Individuals exposed to tuberculosis should be skin tested immediately and a follow-up test should be done at a later date, if the initial test is negative.

Prompt treatment is extremely important in controlling the spread of tuberculosis for those who have already progressed to active TB disease.

A BCG vaccination to prevent TB is given in some countries with a high incidence of TB, but its effectiveness remains controversial. It is not routinely used in the United States. People who have had BCG may still be skin tested for TB and results of testing (if positive) discussed with one's doctor.

References

Ferrara G, Losi M, Meacci M, et al. Routine Hospital Use of a New Commercial Whole Blood Interferon-(gamma) Assay for the Diagnosis of Tuberculosis Infection. Am J Respir Crit Care Med. 2005 Sep 1;172(5):631-5. Epub 2005 Jun 16.

US Centers for Disease Control. Treatment of Tuberculosis. MMWR 2003; 52.

Diagnostic Standards: Classification of TB in Adults and Children. Am J Respir Crit Care Med 2000; 161.