Tuberculosis - Causes, Symptoms and Treatments
An acute or chronic infection caused by Mycobacterium tuberculosis, tuberculosis (TB) is characterized by pulmonary infiltrates, formation of granulomas with caseation, fibrosis, and cavitation. Globally, tuberculosis is the leading cause of morbidity and mortality. There are 8 to 10 million new cases each year. People living in crowded, poorly ventilated conditions are most likely to become infected.
In patients with strains that are sensitive to the usual antitubercular agents, the prognosis is excellent with correct treatment. However, in those with strains that are resistant to two or more of the major antitubercular agents, mortality is 50%.
Causes of Tuberculosis:
After exposure to M. tuberculosis, roughly 5% of infected people develop active tuberculosis within 1 year; in the remainder, microbes cause a latent infection. The immune system usually controls the tubercle bacillus by killing it or walling it up in a tiny nodule (tubercle). However, the bacillus may lie dormant within the tubercle for years and later reactivate and spread.
Although the primary infection site is the lungs, mycobacteria commonly exist in other parts of the body. A number of factors increase the risk of infection reactivation: gastrectomy, uncontrolled diabetes mellitus, Hodgkin's disease, leukemia, silicosis, acquired immunodeficiency syndrome, and treatment with corticosteroids or immunosuppressives.
Tuberculosis is transmitted by droplet nuclei produced when infected persons cough or sneeze. Persons with a cavity lesion are particularly infectious because their sputum usually contains 1 million to 100 million bacilli per ml. After inhalation, if a tubercle bacillus settles in an alveolus, infection occurs. Cell-mediated immunity to the mycobacteria, which develops about 3 to 6 weeks later, usually contains the infection and arrests the disease.
If the infection reactivates, the body's response characteristically leads to caseation - the conversion of necrotic tissue to a cheeselike material. The caseum may localize, undergo fibrosis, or excavate and form cavities, the walls of which are studded with multiplying tubercle bacilli. If this happens, infected caseous debris may spread throughout the lungs by the tracheobronchial tree.
Sites of extrapulmonary TB include pleura, meninges, joints, lymph nodes, peritoneum, genitourinary tract, and bowel.
Signs and symptoms of Tuberculosis:
In primary infection, after an incubation period of from 4 to 8 weeks, TB is usually asymptomatic but may produce nonspecific symptoms, such as fatigue, weakness, anorexia, weight loss, night sweats, and low-grade fever.
In reactivation, symptoms may include a cough that produces mucopurulent sputum, occasional hemoptysis, and chest pains.
Diagnosis of Tuberculosis:
Diagnostic tests include chest X -rays, a tuberculin skin test, and sputum smears and cultures to identify M. tuberculosis. The following procedures aid diagnosis:
1. Auscultation detects crepitant rales, bronchial breath sounds, wheezes, and whispered pectoriloquy.
2. Chest percussion detects a dullness over the affected area, indicating consolidation or pleural fluid.
3. Chest X-ray shows nodular lesions, patchy infiltrates (mainly in upper lobes), cavity formation, scar tissue, and calcium deposits; however, it may not be able to distinguish active from inactive TB.
4. Tuberculin skin test detects TB infection. Intermediate-strength purified protein derivative (PPD) or 5 tuberculin units (0.1 ml) are injected intracutaneously on the forearm. The test results are read in 48 to 72 hours; a positive reaction (induration of 5 to 15 mm or more, depending on risk factors) develops 2 to 10 weeks after infection in both active and inactive TB. However, severely immunosuppressed patients may never develop a positive reaction.
5. Stains and cultures (of sputum, cerebrospinal fluid, urine, drainage from abscess, or pleural fluid) show heatsensitive, nonmotile, aerobic, acid-fast bacilli.
Treatment of Tuberculosis:
Antitubercular therapy with daily oral doses of isoniazid, rifampin, and pyrazinamide (and sometimes ethambutol) for at least 6 months usually cures tuberculosis. After 2 to 4 weeks, the disease generally is no longer infectious. The patient can resume his lifestyle while taking medication.
Patients with atypical mycobacterial disease or drug-resistant TB may require treatment with second-line drugs, such as capreomycin, streptomycin, para-aminosalicylic acid, cycloserine, amikacin, and quinolone drugs. Because of the consequences of inadequate or incomplete treatment, direct observed therapy (DOT) to prevent noncompliance is increasingly being employed.
Special considerations of Tuberculosis:
1. Isolate the infectious patient in a quiet, well-ventilated room until he's no longer contagious.
2. Teach the patient to cough and sneeze into tissues and to dispose of all secretions properly. Place a covered trash can nearby or tape a waxed bag to the side of the bed for used tissues.
3. Instruct the patient to wear a mask when outside his room. Visitors and hospital personnel should wear masks when they are in the patient's room.
4. Remind the patient to get plenty of rest and to eat balanced meals. If the patient is anorectic, urge him to eat small meals throughout the day. Record weight weekly.
6. If the patient receives ethambutol, watch for optic neuritis; if it develops, discontinue the drug. If he receives rifampin, watch for hepatitis and purpura. Also observe the patient for other complications such as hemoptysis.
7. Emphasize the importance of regular follow up examinations, and instruct the patient and his family concerning the signs and symptoms of recurring TB.
8. Advise persons who have been exposed to infected patients to receive tuberculin tests and, if necessary, chest X-rays and prophylactic isoniazid.
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