13 Pulmonary tuberculosis

Overview/pathophysiology

Tuberculosis (TB) is an infectious disease caused primarily by Mycobacterium tuberculosis. In the United States an estimated 10 to 15 million persons are infected with this organism, the majority of whom have latent tuberculosis infection (LTBI) in which the bacteria are in the body (usually the lungs) in a dormant form that neither causes disease nor is communicable to other persons. A small proportion of persons (about 10%) with LTBI will develop active TB in their lifetimes.

For many years (from 1953 to 1984), reported cases of TB in the United States decreased almost 6% each year, and there was a general perception that TB was no longer a problem. This decline was due to many factors, including improved living conditions (less crowding and better ventilation), better nutrition, and antituberculosis drugs. As a result, the public health infrastructure to support TB control weakened as other diseases, for example, human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS), became more prominent. It was not until the late 1980s that the link between TB and HIV/AIDS became apparent as was manifested partially by multidrug-resistant (MDR) TB outbreaks occurring in seven hospitals between 1990 and 1992, resulting in many cases of LTBI, TB disease, and death. In addition, reported cases of TB increased 20% between 1985 and 1992. After the hospital outbreaks and other changes in administrative and legislative support to control TB, cases have steadily declined again in most areas of the country. In 2008, there were fewer than 13,000 reported cases of TB in the United States, more than half of which were among foreign-born persons. Worldwide, TB remains a leading cause of death in undeveloped countries, with the World Health Organization estimating that approximately one third of the world’s population is infected with M. tuberculosis.

M. tuberculosis is transmitted by the airborne route via minute, invisible particles called droplet nuclei. When individuals with TB disease of the lungs or throat cough, sneeze, speak, or sing, their respiratory secretions harbor TB organisms that are expelled into the air and transform quickly into tiny droplet nuclei that can remain suspended in air for several hours, depending on the environment (especially ventilation). In order to become infected, another person must breathe the air containing the droplet nuclei. A person’s natural defenses of the nose and upper airway and immune system will often prevent sufficient numbers of organisms from reaching the alveoli to cause infection. In fact, it generally takes 5 to 200 organisms implanted in the alveoli to cause LTBI. When organisms reach the alveoli, they are ingested by macrophages. Some of the bacilli spread through the bloodstream when the macrophages die; however, the immune system response usually prevents the individual from developing TB disease. Although the majority of TB cases are pulmonary (85%), TB can occur in almost any part of the body or as disseminated disease. About half of people with LTBI who develop active TB (5%) will do so within the first year or two after infection. The remainder (5%) will develop active TB within their lifetimes.

Health care setting

Primary care or long-term care, with possible hospitalization (acute care) resulting from complications

Assessment

For an accurate diagnosis of TB, a complete medical and psychosocial history should be taken along with a physical examination that includes a tuberculin skin test or an interferon gamma release assay (IGRA) blood test (there are currently two Food and Drug Administration [FDA]-approved IGRA tests available: the QuantiFERON®-TB Gold (QFT-G) and T-SPOT®), chest x-ray examination, and sputum examination (including acid-fast bacilli [AFB] smears, cultures, and drug sensitivity studies).

Signs and symptoms:

TB is often suspected based on a group of symptoms that may include productive prolonged cough, fever, night sweats, as well as chest pain, hemoptysis, chills, loss of appetite, unintended weight loss over a short period of time, and tiredness.

Note:

Close contacts of the patient require identification so that they can undergo evaluation for the presence of LTBI. TB is reportable to the Public Health Department.

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