Pneumocystis pneumonia has long been recognized as a cause of morbidity and mortality in immunocompromised populations, particularly those with HIV infection. Pneumocystis colonization-that is, detection of the organism or its DNA, without signs or symptoms of pneumonia-has recently been described, and accumulating evidence suggests that it may be an important clinical phenomenon. Sensitive molecular techniques such as polymerase chain reaction are frequently used to identify Pneumocystis colonization. Low levels of Pneumocystis in the lungs may stimulate pulmonary inflammation and may play a role in the development of lung diseases such as chronic obstructive pulmonary disease. In this review, we discuss evidence for the occurrence of Pneumocystis colonization in animals as well as the epidemiology and risk factors for Pneumocystis colonization in various human populations. We also evaluate the clinical significance of Pneumocystis colonization and its relationship to lung disease.

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Nocturnal symptoms in asthma are frequently underdiagnosed. Obstructive sleep apnea may be prevalent in nocturnal asthma. The Gly16 polymorphism of the beta2-receptor is common in nocturnal asthma. Gastric suppression treatment in patients with both gastroesophageal reflux disease and nocturnal asthma improved the peak expiratory flow rate. Continuous positive airway pressure improves nocturnal symptoms but not lung function tests.

Aspiration pneumonia is prevalent in community-acquired pneumonia. Further studies are needed to elucidate the effects of sympathetic nervous system and aspiration pneumonitis as primers for lung infection. Predicting aspiration risk is difficult and newer diagnostic tools are necessary. Antimicrobials used in aspiration pneumonia have similar success rates although the development of resistant organisms must be monitored.