TB

Alternative names
Pulmonary tuberculosis; Tuberculosis - pulmonary; Consumption

Definition
Pulmonary tuberculosis is a contagious bacterial infection caused by Mycobacterium tuberculosis (TB). 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 Mycobacterium 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. In the United States, the majority of people will recover from primary TB infection without further evidence of the disease.

Pulmonary TB develops in the minority of people whose immune systems do not successfully contain the primary infection. The disease may occur within weeks after the primary infection, or it may lie dormant for years before causing disease.

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, but without effective therapy, the disease becomes progressive.

The risk of contracting TB increases with the frequency of contact with people who have the disease, and with crowded or unsanitary living conditions and poor nutrition. An increased incidence of TB has been seen recently in the United States. Factors that may contribute to the increase in tuberculous infection are:

     
  • Increase in HIV infection  
  • Increasing 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 damaged immune systems from 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.

The incidence of tuberculosis in the U.S. has been around 10 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

     
  • Initially not apparent, or limited to minor cough and mild fever  
  • Fatigue  
  • Weight loss  
  • Coughing up blood  
  • Fever and night sweats  
  • Cough producing phlegm

Additional symptoms that may be associated with this disease:

     
  • Wheezing  
  • Sweating, excessive  
  • Chest pain  
  • Breathing difficulty

Signs and tests
Examination of the lungs by stethoscope (auscultation) can reveal crackles. Enlarged or tender lymph nodes may be present in the neck or other areas. Fluid may be detectable around a lung (pleural effusion). Clubbing of the fingers or toes may be present.

Tests often include:

     
  • Chest X-ray  
  • Sputum cultures  
  • Tuberculin skin test  
  • Bronchoscopy  
  • Thoracentesis  
  • Chest CT  
  • Rarely, biopsy of the affected tissue (typically lungs, pleura, or lymph nodes) is required

Treatment
The goal of treatment is to cure the infection with antitubercular drugs. Daily oral doses of multiple drugs that may include combinations of rifampin, isoniazid, pyrazinamide, ethambutol, or occasionally others, are continued until culture results (if available) showing the drug sensitivity of the mycobacterial infection help to guide the selection of drugs.

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 durations 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 resolved on drug therapy. Normal activity can be continued after the contagious period.

Support Groups

The stress of illness can often 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, with improvement seen in the chest X-ray lagging behind clinical improvement. 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 may rarely affect 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) is a screening test for TB used in high risk populations or in those who may have been exposed to TB (such as all health care workers).

A positive test indicates prior TB exposure and indications for preventive therapy should be discussed with your doctor. Individuals exposed to tuberculosis should be skin tested immediately and the skin test repeated 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.

Johns Hopkins patient information

Last revised: December 7, 2012
by Mamikon Bozoyan, M.D.

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