eMedicine Specialties > Infectious Diseases > Mycobacterial Infections

Tuberculosis

Author: Thomas Herchline, MD, Professor of Medicine, Wright State University Boonshoft School of Medicine; Medical Director, Public Health, Dayton and Montgomery County, Ohio
Coauthor(s): Judith K Amorosa, MD, FACR, Clinical Professor and Program Director, Department of Radiology, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School; Consulting Staff, Department of Radiology, Robert Wood Johnson University Hospital
Contributor Information and Disclosures

Updated: Nov 11, 2009

Introduction

Background

Tuberculosis (TB) is the most common cause of infectious disease–related mortality worldwide. The World Health Organization estimates that 2 billion people have latent TB, while another 3 million people worldwide die of TB each year.1

Although TB rates are decreasing in the United States, the disease is becoming more common in many parts of the world. In addition, the prevalence of drug-resistant TB is also increasing worldwide. Co-infection with HIV has been an important factor in the emergence and spread of resistance.2 New TB treatments are being developed,3 and new TB vaccines are currently under investigation.4

Pathophysiology

Humans are the only known reservoir for Mycobacterium tuberculosis. TB is transmitted by airborne droplet nuclei, which may contain fewer than 10 bacilli. TB exposure occurs by sharing common airspace with an individual who is in the infectious stage of TB. When inhaled, droplet nuclei are deposited within the terminal airspaces of the lung. Upon encountering the bacilli, macrophages ingest and transport the bacteria to regional lymph nodes.

The bacilli have 4 potential fates: (1) They may be killed by the immune system, (2) they may multiply and cause primary TB, (3) they may become dormant and remain asymptomatic, or (4) they may proliferate after a latency period (reactivation disease). Reactivation TB may occur following either (2) or (3) above.

Frequency

United States

The US Centers for Disease Control and Prevention (CDC) has been recording detailed epidemiologic information on TB since 1953. The incidence of TB has been declining since the early 20th century because various factors, including basic infection-control practices (isolation). Beginning in 1985, a resurgence of TB was noted. The increase was observed primarily in ethnic minorities and especially in persons infected with HIV. TB control programs were revamped and strengthened across the United States.

After peaking at 25,287 cases in 1993, the number of reported cases began to fall again. In 2007, 13,293 cases of TB were reported.5 This corresponds to a rate of 4.4 cases per 100,000 population. The overall frequency of TB is 9.7 times higher in foreign-born persons than in native-born persons, accounting for a steadily increasing proportion of all reported TB cases. In 2007, 7,690 cases of TB (58.5% of all US cases) were reported among foreign-born persons. More than half (52%) of TB cases involving foreign-born individuals in 2007 were reported in persons from 4 countries: Mexico (24%), the Philippines (12.4%), India (8%), and Vietnam (7.4%). An estimated 10-15 million people in the United States have latent TB infection.

International

An estimated 20-33% of the world's population is infected with M tuberculosis. Countries with the highest prevalence include Russia, India, Bangladesh, Pakistan, Indonesia, Philippines, Vietnam, Korea, China, Tibet, Hong Kong, Egypt, most sub-Saharan African countries, Brazil, Mexico, Bolivia, Peru, Colombia, Dominican Republic, Ecuador, Puerto Rico, El Salvador, Nicaragua, Haiti, Honduras, and areas undergoing civil war (eg, Balkan countries). The prevalence of TB in countries in Eastern Europe is intermediate. The prevalence of TB is lowest in Costa Rica, western and northern Europe, the United States, Canada, Israel, and most countries in the Caribbean. Multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) are becoming increasingly significant.6 Genotyping studies have shown that between 63% and 75% of TB cases progress to XDR-TB through acquisition of resistance.7

Mortality/Morbidity

The case-fatality rate for TB was 50% for untreated patients before the advent of antibiotic therapy. TB-related deaths worldwide are estimated at 3 million per year. In the United States, the mortality rate of TB dropped from 12.4 deaths per 100,000 population in 1953 to 0.2 deaths per 100,000 population in 2004; this is approximately 4% per newly identified case.

  • MDR-TB cases are associated with a higher mortality rate. The mortality rate is also higher in patients with underlying diseases that predispose to active TB.
  • The mortality rate associated with untreated congenital TB is 50%. Congenital TB can mimic congenital syphilis or cytomegalovirus (CMV) infection.

Race

Based on 2007 CDC data, the frequency of TB in Hispanics, blacks, and Asians were 7.6, 8.5, and 23.5 times higher than in whites, respectively.1 However, race is not clearly an independent risk factor, as foreign-born persons account for 77% of TB cases among Hispanics and 96% of TB cases among Asians, but only 29% of TB cases among blacks. Risk is best defined based on social, economic, and medical factors.

Sex

Despite the fact that TB rates have declined in both sexes in the United States, certain differences exist. TB rates in women decline with age, but, in men, rates increase with age. Men are more likely to have a positive tuberculin skin test result. The reason for these differences may be social rather than biological in nature.

Age

  • In the United States, more than 60% of TB cases occur in persons aged 25-64 years; however, the age-specific risk is highest in persons older than 65 years.1
  • TB infection in infants and young children (≤5 y) always indicates recent transmission. Untreated TB in this age group may result in life-threatening meningitis or disseminated disease.
  • Elderly individuals with TB may not display typical signs and symptoms of TB infection because they may not mount a good immune response. Active TB infection in this age group may manifest as nonresolving pneumonitis. Obesity in elderly patients has been associated with a lower risk for pulmonary TB.8

Clinical

History

  • Pulmonary tuberculosis (TB): Typical symptoms of pulmonary TB include a productive cough, fever, and weight loss. Patients with pulmonary TB occasionally present with hemoptysis or chest pain. Other systemic symptoms include anorexia, fatigue, and night sweats.
  • Tuberculous meningitis: Patients with tuberculous meningitis may present with a headache that is either intermittent or persistent for 2-3 weeks. Subtle mental status changes may progress to coma over a period of days to weeks. Fever may be low-grade or absent.
  • Skeletal TB: The most common site of skeletal TB involvement is the spine (Pott disease). Symptoms include back pain or stiffness. Lower-extremity paralysis occurs in up to half of patients with undiagnosed Pott disease. Tuberculous arthritis usually involves only one joint. Although any joint may be involved, the hips and knees are affected most commonly, followed by the ankle, elbow, wrist, and shoulder. Pain may precede radiographic changes by weeks to months.
  • Genitourinary TB: Reported symptoms of genitourinary TB include flank pain, dysuria, and frequency. In men, genital TB may manifest as epididymitis or a scrotal mass. In women, genital TB may mimic pelvic inflammatory disease. TB is the cause of approximately 10% of sterility cases in women worldwide and approximately 1% in industrialized countries.
  • Gastrointestinal TB: Any site along the gastrointestinal tract may become infected. Symptoms of gastrointestinal TB are referable to the site infected, including the following: nonhealing ulcers of the mouth or anus; difficulty swallowing with esophageal disease; abdominal pain mimicking peptic ulcer disease with stomach or duodenal infection; malabsorption with infection of the small intestine; and pain, diarrhea, or hematochezia with infection of the colon.
  • Tuberculous lymphadenitis (scrofula): The most common site of tuberculous lymphadenitis is in the neck along the sternocleidomastoid muscle. It is usually unilateral and causes little or no pain. Advanced cases of tuberculous lymphadenitis may suppurate and form a draining sinus.
  • Cutaneous TB: Direct inoculation may result in an ulcer or wartlike lesion. Contiguous spread from an infected lymph node typically results in a draining sinus. Hematogenous spread may result in a reddish brown plaque on the face or extremities (lupus vulgaris) or tender nodules or abscesses.

Physical

Physical examination findings associated with TB depend on the organs involved.

  • Patients with pulmonary TB have abnormal breath sounds, especially over the upper lobes or areas involved.
  • Signs of extrapulmonary TB differ depending on the tissues involved. Signs may include confusion, coma, neurologic deficit, chorioretinitis, lymphadenopathy, and cutaneous lesions (see History).
  • Postnatal TB is contracted via the airborne route. The most common findings of postnatal TB include adenopathy and a lung infiltrate. However, the chest radiographic findings may be normal in infants with disseminated disease. Many experts increase the treatment duration to 9 or 12 months because of the possible impaired immune system in children younger than 12 months. Bacille Calmette-Guérin (BCG) vaccine is not recommended in infants in the United States but is commonly used around the world.

Causes

M tuberculosis is a slow-growing organism, requiring 4-8 weeks for visible growth on solid medium. The organism grows in parallel groups called cords (as seen in the image below). It retains many stains after decoloration with acid-alcohol, which is the basis of acid-fast stains.

Tuberculosis. Acid-fast bacillus smear showing ch...

Tuberculosis. Acid-fast bacillus smear showing characteristic cording in Mycobacterium tuberculosis.

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Tuberculosis. Acid-fast bacillus smear showing ch...

Tuberculosis. Acid-fast bacillus smear showing characteristic cording in Mycobacterium tuberculosis.


More on Tuberculosis

Overview: Tuberculosis
Differential Diagnoses & Workup: Tuberculosis
Treatment & Medication: Tuberculosis
Follow-up: Tuberculosis
Multimedia: Tuberculosis
References
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References

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Further Reading

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Contributor Information and Disclosures

Author

Thomas Herchline, MD, Professor of Medicine, Wright State University Boonshoft School of Medicine; Medical Director, Public Health, Dayton and Montgomery County, Ohio
Thomas Herchline, MD is a member of the following medical societies: American College of Physicians, American Society for Microbiology, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

Coauthor(s)

Judith K Amorosa, MD, FACR, Clinical Professor and Program Director, Department of Radiology, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School; Consulting Staff, Department of Radiology, Robert Wood Johnson University Hospital
Judith K Amorosa, MD, FACR is a member of the following medical societies: American College of Radiology, American Roentgen Ray Society, Association of University Radiologists, Radiological Society of North America, and Society of Thoracic Radiology
Disclosure: Nothing to disclose.

Medical Editor

John M Leedom, MD, Professor of Medicine, Keck School of Medicine, University of Southern California; Chief, Division of Infectious Diseases, Department of Internal Medicine, Los Angeles County, University of Southern California Medical Center
John M Leedom, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians-American Society of Internal Medicine, American Society for Microbiology, Infectious Diseases Society of America, International AIDS Society, and Phi Beta Kappa
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Aaron Glatt, MD, Professor of Clinical Medicine, New York Medical College; President and CEO, Former Chief Medical Officer, Departments of Medicine and Infectious Diseases, New Island Hospital
Aaron Glatt, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physician Executives, American College of Physicians, American College of Physicians-American Society of Internal Medicine, American Medical Association, American Society for Microbiology, American Thoracic Society, American Venereal Disease Association, Infectious Diseases Society of America, International AIDS Society, and Society for Healthcare Epidemiology of America
Disclosure: Nothing to disclose.

CME Editor

Eleftherios Mylonakis, MD, Clinical and Research Fellow, Department of Internal Medicine, Division of Infectious Diseases, Massachusetts General Hospital
Eleftherios Mylonakis, MD is a member of the following medical societies: American Association for the Advancement of Science, American College of Physicians, American Society for Microbiology, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

Chief Editor

Burke A Cunha, MD, Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital
Burke A Cunha, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

 
 
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