Manejo clínico de las neumonías adquiridas en la comunidad

Abstract

Streptococcus pneumoniae is the most common cause of CAP, at a rate of 9.6% to 48.8% of cases with an etiologic diagnosis. Mycoplasma pneumoniae is one of the primary causes of pneumonia in young patients, mainly those under 20 years old. Chlamydia pneumoniae can affect young patients and adults with underlying diseases, causing 5%-15% of CAP episodes. Chlamydia psittaci and Coxiella burnetii are uncommon causes of CAP, as are viral influenza and respiratory syncytial virus, which can cause pneumonia in adults during the cold months. Legionella pneumophila accounts for 2%-6% of CAP in the majority of series of hospitalized patients. Haemophilus influenzae is an infrequent cause of pneumonia in adults, affecting mainly elderly people and patients with underlying diseases, such as chronic airway obstruction and tobacco use. Moraxella catarrhalis mainly affects patients with underlying bronchopulmonary disease, such as chronic airway obstruction. Staphylococcus aureus is also an uncommon causal agent, accounting for 1.7% of 2145 cases of pneumonia,5 although it is more frequent in patients with severe CAP. Aerobic gram-negative bacilli, such as Klebsiella spp. (1.2% of 2458 cases of CAP) and Escherichia coli (0.8%) are infrequent causes of CAP5. In severe cases, the frequency of enterobacteria is higher, causing 11.8% of the episodes. Pseudomonas aeruginosa is a quite infrequent causal agent, accounting for 0.5% of cases without criteria of severity and with an etiologic diagnosis, and 3.8% of severe cases5. The frequency of CAP involving anaerobic microorganisms is unknown, though it has been estimated at about 10%. The most common predisposing factor is the aspiration of oropharyngeal secretions during episodes of altered mental status or other circumstances favoring this event, such as dysphagia, intestinal obstruction, periodontal disease, tonsillectomy or dental extractions. In series of patients with severe community pneumonia, the most frequent agents are S. pneumoniae, followed by Legionella spp. and H. influenzae6 and other gram-negative bacilli, and aspiration pneumonia, whereas in series of cases treated on an outpatient basis, pneumococcus, Chlamydia spp. and M. pneumoniae predominate. The relationships among the various etiologic agents and predisposing factors are summarized in Table 1.