Antibiotic Resistance in Community-Acquired Pneumonia Pathogens

The overwhelming majority of cases of community-acquired pneumonia (CAP) can be treated with the standard antibiotic regimens of a macrolide and cephalosporin or a fluoroquinolone. Despite high rates, current levels of β-lactam resistance generally do not result in treatment failure for patients with CAP when appropriate agents and doses are used. Following the introduction of the pneumococcal conjugate vaccines, the incidence of invasive pneumococcal disease declined drastically, coinciding with a decrease in penicillin resistance. Risk factors for methicillin-resistant S. aureus follow two patterns: (1) healthcare-associated risk factors and (2) pneumonia from exotoxin-producing community-acquired strains. The latter is associated with need for antibiotics which inhibit protein synthesis for optimal management. Since 2000, macrolide-resistance in M. pneumoniae has rapidly emerged worldwide, especially in Asian countries. The inability to routinely culture H. influenzae suggests that macrolide and β-lactam resistance, while present, is not a big issue. Unless risk factors for a hospital-associated strain are present, the most common Enterobacteriaceae to cause CAP, including Escherichia coli and Klebsiella, are generally susceptible to usual CAP antibiotics. Given the limited role of antibiotic resistance in CAP, a strong rationale is needed for use of antibiotics other than the standard β-lactam/macrolide or fluoroquinolone regimens.