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(too-bĕr″kyŭ-lō′sĭs, tū- )
[tubercle + -osis]
ABBR: TB An infectious disease caused by the tubercle bacillus, Mycobacterium tuberculosis, and characterized pathologically by inflammatory infiltration, formation of tubercles, caseation, necrosis, abscesses, fibrosis, and calcification. It most commonly affects the respiratory system, but other parts of the body such as the gastrointestinal and genitourinary tracts, bones, joints, nervous system, lymph nodes, and skin may also become infected. Fish, amphibians, birds, and mammals (esp. cattle) are subject to the disease. Three types of the tubercle bacillus exist: human, bovine, and avian. Humans may become infected by any of the three types, but in the U.S. the human type predominates. Infection usually is acquired from contact with an infected person or an infected cow or through drinking contaminated milk. In the U.S., about 10 to 15 million persons have been infected with tuberculosis. In 2005 about 14,000 active cases were reported in the U.S.; in 2009, 11,545 new cases were reported; and in 2013 nearly 10,000 new cases in the U.S. were reported. Worldwide, about 2 billion people harbor the infection; about 9 million have active disease; an estimated 1.4 million die from TB each year. The percentage of drug-resistant TB cases varies internationally.
Tuberculosis usually affects the lungs, but the disease may spread to other organs, including the gastrointestinal and genitourinary tracts, bones, joints, nervous system, lymph nodes, and skin. Macrophages surround the bacilli in an attempt to engulf them but cannot, producing granulomas with a soft, cheesy (caseous) core. From this state, lesions may heal by fibrosis and calcification and the disease may exist in an arrested or inactive stage. Depending on the person’s immune status and other factors, the disease may become reactivated as pulmonary TB or disseminated infection. Reactivation or exacerbation of the disease or reinfection gives rise to the chronic progressive form.
The incidence of TB declined steadily from the 1950s to about 1990, when the AIDS epidemic, an increase in the homeless population, an increase in immigrants from areas where TB is endemic, and a decrease in public surveillance caused a resurgence of the disease. Populations at greatest risk for TB include patients with HIV, immigrants from Asia, and elsewhere, the urban homeless, alcoholics and other substance abusers, those incarcerated in prisons and psychiatric facilities, nursing home residents, patients taking immunosuppressive drugs, and people with chronic respiratory disorders, diabetes mellitus, renal failure, or malnutrition. People from these risk groups should be assessed for TB if they develop pneumonia; all health care workers should be tested annually.
Currently the only vaccine available to prevent tuberculosis is the bacille Calmette-Guérin (BCG) vaccine. It has limited effectiveness but is used in regions of the world where TB is endemic.
TUBERCULOSIS anteroposterior x-ray of a patient diagnosed with advanced bilateral pulmonary tuberculosis (SOURCE: Centers for Disease Control and Prevention)
TUBERCULOSIS Reported tuberculosis cases in the United States, 1982-2010 (adapted from Centers for Disease Control and Prevention); SEE: immunological therapy; SEE: tuberculin skin test; SEE: BCG vaccine
Approx. 4 to 12 weeks elapse between the time of infection and the time a demonstrable primary lesion or positive tuberculin skin test (TST) occurs.
Pulmonary TB produces chronic cough, sputum, fevers, sweats, and weight loss. TB may also cause neurological disease (meningitis), bone infections, urinary bleeding, and other symptoms if it spreads to other organs. TB is a major cause of infertility around the world.
Tests for diagnosing latent infection with tuberculosis include a positive TST or a blood assay. A presumptive diagnosis of active disease is made by finding acid-fast bacilli in stained smears from sputum or other body fluids. The diagnosis is confirmed by isolating M. tuberculosis in cultures or rapid nucleic acid test probes.
Regimens for TB have been developed for patients, depending on their HIV status, the prevalence of multidrug-resistant disease in the community, drug allergies, and drug interactions. Uncomplicated TB in the non-HIV-infected patient is typically treated with a four-drug regimen for 6 months. Regimens change: prescribers should consult published guidelines for current standards of care. Common drugs include isoniazid (INH), rifampin (RIF), ethambutol (EMB), pyrazinamide, ciprofloxacin, and rifapentin. Medications are typically given in combinations rather than alone. A long course of therapy may be prescribed for patients co-infected with HIV/AIDS or for patients with drug-resistant bacilli. Multiply drug-resistant TB (MDR-TB) is tuberculosis resistant to either INH or RIF. Extensively drug-resistant TB (XDR-TB) is resistant to INH or RIF, any fluoroquinolone (such as ciprofloxacin), and at least one parenteral TB drug. Both MDR-TB and XDR-TB have very high mortality rates.
SEE: multi-drug resistant tuberculosis
All patients with HIV should be tested for TB, and all patients with TB should be tested for HIV, because about one fourth of all patients with one disease will be infected with the other.
All patients suspected of or confirmed to have TB should be placed in airborne isolation until they are no longer infectious. Health care professionals and visitors should wear particulate respirators when in the patient’s room. Patients should be taught to cough and sneeze into tissues, and to dispose of secretions in a lined bag taped to the side of the bed or in a covered disposal. The patient should wear a mask when outside the isolation room for any reason. Patients should be observed for complications such as hemoptysis, bone or back pain, and bloody urine. The patient and family or other support persons should be taught about the importance of regular follow-up visits, of following and completing the treatment regimen exactly as prescribed, of adverse effects to be reported, and of signs and symptoms of recurring TB. Persons who have been exposed to an infected patient should receive a TB test; chest x-rays and prophylactic INH also may be prescribed.
TUBERCULOSIS Pleural fluid with plasma cells (×1000)