– A recurrent, chronic, infectious pulmonary and extrapulmonary disease characterized by formation of granulomas with caseation, fibrosis, and cavitation.
Causes and Incidence
Tuberculosis (TB) is caused by spore-forming mycobacteria (Mycobacterium tuberculosis, M. bovis, or M. africanum). In developed countries the infection is airborne and is spread by inhalation of infected droplets. In underdeveloped countries (Africa, Asia, South America), transmission also occurs by ingestion or by skin invasion, particularly when bovine TB is poorly controlled. The incidence varies widely by country, age, race, sex, and socioeconomic status. Those at greatest risk are children under age 3 and adults over age 65; blacks and Hispanics; males; silicone and asbestos workers (particularly those who smoke); malnourished individuals; people living in unsanitary, crowded conditions; those in institutional settings; drug and alcohol abusers; the chronically ill; and immunosuppressed individuals. The incidence of TB has risen precipitously in the United States with the advent of HIV infection and among certain immigrant populations. The annual incidence in the United States is currently estimated at 14 per 100,000 people.
TB has three stages: (1) primary (initial) infection; (2) latent (dormant) infection; and (3) recrudescent (postprimary) disease. During the first stage, the mycobacteria invade the tissues at the port of entry (usually the lungs) and multiply over a period of approximately 3 weeks. They form a small inflammatory lesion in the lung before traveling to the regional lymph nodes and throughout the body, forming additional lesions. The number of lesions formed depends on the number of invading bacteria and the general resistance of the host. This stage is generally asymptomatic.
Lymphocytes and antibodies mount a fibroblastic response to the invasion that encases the lesions, forming noncaseating granulomas. This marks the latent stage, and the individual may remain in this stage for weeks to years, depending on the body’s ability to maintain specific and nonspecific resistance. Stage three occurs when the body is unable to contain the infection, and a necrotic and cavitation process begins in the lesion at the entry port or in other body lesions. Caseation occurs and the lesions may rupture, spreading necrotic residue and bacilli throughout the surrounding tissue. Disseminated bacteria form new lesions, which in turn become inflamed and form noncaseating granulomas and then caseating necrotic cavities. The lungs are the most common site for recrudescent disease, but it may occur anywhere in the body. Untreated disease has many remissions and exacerbations.
Manifestations vary with the systems involved. Symptoms are rarely seen until the recrudescent stage. Individuals are communicable whenever bacilli are present in the sputum.
Weight loss, fatigue, generalized weakness, anorexia; slight fever with chills and night sweats; nonproductive cough that eventually becomes productive with mucopurulent sputum; tachycardia; dyspnea on exertion; hemoptysis
Pericarditis with precordial chest pain, fever, ascites, edema, and distention of neck veins
Peritonitis with acute abdominal pain, abdominal distention, vomiting, anorexia, weight loss, night sweats; gastrointestinal bleeding, bowel obstruction
Meningitis with headache, vomiting, fever, declining consciousness, and neurologic deficit
Joint pain, swelling, tenderness, deformities; limitation of motion
Urgency, frequency, dysuria, hematuria, pyuria; infertility, amenorrhea, vaginal bleeding and discharge; salpingitis with lower abdominal pain
Enlarged lymph nodes
Complications include massive destruction of lung tissue, leading to pneumothorax, pleural effusion, pneumonia, and respiratory failure; brain abscess; cardiac tamponade; vertebral collapse and paralysis; liver failure; renal failure; and generalized, massive dissemination of disease that usually is fatal. New drug-resistant strains of tuberculosis are emerging, leading to more frequent progression to complications.
Skin tests (purified protein derivative/Mantoux)
Positive reaction indicates past infection and presence of antibodies; it is not indicative of active disease
Positive for causative agent within 2 to 3 weeks of onset of active disease; it is not positive during latency
Acid-fast sputum smear
Positive for acid-fast bacillus
Positive for causative agent
Pleural needle biopsy
Positive for causative agent
May reveal cavitation, calcification, parenchymal infiltrate; not diagnostically definitive
Drainage of pulmonary abscesses; correction of complications such as intestinal obstruction or urethral stricture.
Antiinfective drugs in combinations of primary drugs or primary and secondary drugs to combat causative agent (new strains of bacillus are occurring that are resistant to traditional primary drugs); antiinfective drugs (isoniazid) as chemoprophylaxis in individuals who have converted from a negative to a positive skin test, particularly those with HIV or other immune-suppressed conditions, insulindependent diabetics, those on prolonged corticosteroid therapy, small children, and health care workers who are regularly exposed.
Sputum precautions until negative sputums are evident (10 to 14 days after start of drug therapy); management usually on an outpatient basis unless the disease is in an advanced state with complications; instruction about the importance of uninterrupted drug therapy and the need for periodic recultures of sputum throughout drug therapy, which may last a year or longer; skin testing and examination of close contacts at the time of initial diagnosis and again in 2 to 3 months; long-term medical follow-up to prevent recurrence.