Pulmonary Tuberculosis

Etiology, Prevalence, and Epidemiology

Tuberculosis (TB) is a chronic recurrent contagious infection caused by Mycobacterium tuberculosis. M. tuberculosis is an aerobic, nonmotile, non–spore-forming rod that is highly resistant to drying, acid, and alcohol. It is transmitted person to person via droplet nuclei containing the organism and spread mainly by coughing. The contagiousness of a patient with TB increases with greater extent of disease, the presence of cavitation, the frequency of coughing, and the virulence of the organism. The risk of developing active TB is the greatest in patients with altered host cellular immunity. These include extremes of age, malnutrition, cancer, immunosuppressive therapy (including steroids and anti–tumor necrosis factor drugs), human immunodeficiency virus (HIV) infection, end-stage renal disease, and diabetes.

In 2014 9.6 million people were estimated to develop TB, and 1.5 million died of the disease, 0.4 million of whom were HIV positive. Of the estimated 9.6 million new cases in 2014, 58% were in Southeast Asia and Western Pacific regions and 28% in the Africa region. During 2014 a total of 9407 confirmed TB cases (3.1 cases per 100,000 population) were reported in the United States. Slightly more than half (54%) of US cases were in foreign-born persons. It is estimated that 43 million lives were saved between 2000 and 2014 through effective diagnosis and treatment. To keep the efforts for global elimination of TB, from 2016 the World Health Organization hopes to end the global TB epidemic by implementing the End TB Strategy, which serves to reduce the number of TB deaths by 90% by 2030, cut new cases by 80%, and ensure that no family is burdened with catastrophic costs resulting from TB.

HIV infection is the strongest known risk factor for progression from latent to active TB. Globally, 12% of the 9.6 million new TB cases in 2014 were HIV positive, and TB killed 0.4 million HIV-positive people. The majority of these patients live in countries with limited health care resources—Africa and Asia. The incidence of TB in these countries is increasing. Immune restoration induced by highly active antiretroviral therapy (HAART) in developed countries has considerably improved the outcome of HIV-positive patients and reduced the prevalence of opportunistic infection and TB in these patients. However, HIV-associated TB continues to occur in countries where HAART is widely used and is seen in patients on antiretroviral treatment. Furthermore, HAART may result in paradoxical worsening of TB manifestations in patients with immune reconstitution inflammatory syndrome (IRIS) (see Chapter 15 ).

Clinical Presentation

Patients with active pulmonary TB may be asymptomatic, have mild or progressive dry cough, or present with multiple symptoms, including fever, fatigue, weight loss, night sweats, and productive cough. Elderly patients with pulmonary TB may have different clinical presentations, including more frequent dyspnea and comorbid medical conditions, such as cardiovascular disease, diabetes, and chronic obstructive pulmonary disease.