Key Clinical Questions
When should tuberculosis be suspected in the inpatient setting?
What diagnostic testing should be performed in patients with suspected tuberculosis?
What precautions are necessary for patients with possible tuberculosis? When may they be discontinued?
What treatment regimen should be begun for patients with newly diagnosed tuberculosis? What monitoring is appropriate in patients being treated for tuberculosis?
A global pandemic of tuberculosis (TB) that began three centuries ago continues today, although globally, rates have begun to decline for the first time over the past few years. According to estimates from the World Health Organization, 9.4 million people developed active TB in 2013, and 1.5 million died. Tuberculosis remains the leading cause of death in the HIV-infected, accounting for 26% of acquired immunodeficiency syndrome (AIDS)-related deaths throughout the world. The incidence of TB is highest in Asia, Africa, Latin America, Russia, and Eastern Europe (Figure 200-1). Rates are substantially lower in developed countries, where TB is increasingly a disease of the foreign born. However, some populations in developed nations have a relatively high incidence of the disease, including homeless persons, injection drug users, incarcerated persons, and some aboriginal populations. Another group at risk in developed nations is the elderly. Rates of TB in the developed world 50 years ago were similar to rates in developing countries today. Older patients born and raised in developed nations therefore have a higher likelihood of developing active TB than younger patients, due to the risk of late reactivation of latent infection.
Tuberculosis incidence in 2005, based on World Health Organization data. (Courtesy of the Stop TB Department, WHO; with permission.)
As TB in the developed world has become uncommon, the diagnosis is often overlooked, even when in retrospect it should have been fairly apparent. Unfortunately, because pulmonary TB may be highly contagious, delays in diagnosis may have disastrous implications not only for the patient, but also for family, friends, and other close contacts, including health care workers.
Tuberculosis is caused almost exclusively by Mycobacterium tuberculosis. Rarely, it is caused by the related organism Mycobacterium bovis, acquired from infected cattle or contaminated milk products. M. tuberculosis is transmitted almost exclusively through the respiratory route by microscopic droplet nuclei. These particles are small enough to remain airborne for long periods of time and to be inhaled directly into the terminal alveoli, typically in the lower lung zones. Droplet nuclei are produced when a patient with pulmonary TB speaks, coughs, or sneezes. Rarely, droplet nuclei may arise from other activities, such as irrigation of TB-infected areas during surgery, dressing changes of draining wounds, or emptying of containers of infectious fluid.
M. tuberculosis has adapted to survive within alveolar macrophages, the cells that normally would be expected to eradicate it. Within the ...