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Introduction

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Pulmonary tuberculous diseases are contagious infections caused by bacterial organisms or bacilli of the Mycobacterium family (Mycobacteriaceae). The most common species is tuberculosis but other types produce similar pathologic changes. The disease is spread by the aerolization of respiratory secretions, and infection occurs by inhalation of the tubercle bacilli (TB). Not everyone infected with TB will become sick immediately. Most patients are asymptomatic because of the host's immune-cell-mediated defense mechanisms, which entrap and wall off the bacilli, thereby containing the infection. The isolated bacilli may form granulomas which may lie dormant for years. Others will experience a short illness associated with malaise, low-grade fever, cough, and weight loss. If the body's immunity becomes compromised, a full-blown infection may ensue. Most frequently, these patients will develop extensive pulmonary infiltrates with a febrile illness and dyspnea associated with the concomitant pneumonia. If the walled-off granulomas break down, cavities form and accumulate secretions causing a productive cough. Infection of the pleural lining (pleurisy) may result in chest wall pain or pleural effusions with shortness of breath. Spontaneous pneumothorax may occur as a consequence of excessive coughing and will present with acute dyspnea. Long-standing infections may result in parenchymal destruction, bronchiectasis with erosion into adjacent pulmonary arteries (Rasmussen's aneurysm)1, and massive hemoptysis.2 These large cavities may lead to secondary fungal infection with Aspergillus (see Chapter 102). In some patients, extensive lung destruction can produce chronic lung collapse and contraction.

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Incidence

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The World Health Organization estimates that one-third of the world's population is currently infected with TB bacillus and 5% to 10% of those infected become infectious or sick at some stage during their lifetime. Individuals with HIV/AIDS are most at risk for developing the full-blown infection. The largest number of new cases of TB in 2010 occurred in southeast Asia (35%); however, the incidence of new cases in sub-Saharan Africa is nearly twice that of southeast Asia with 350 cases per 100,000 people. In 2009, over 1.7 million individuals died from TB. Although the incidence of TB appears to be stable or falling, adjusted for population growth, the number of new cases is rising annually (Table 105-1).3

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Table Graphic Jump Location
Table 105-1Estimated TB Incidence, Prevalence, and Mortality, 2009

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