Outcomes in lower respiratory tract infections and the impact of antimicrobial drug resistance

Numerous published studies have documented the rapid rise in antimicrobial drug resistance among common respiratory pathogens, particularly Streptococcus pneumoniae. Yet, surprisingly few studies have evaluated the impact of these in vitro findings on clinical outcomes. Outcomes research is the measurement of the impact of illness and the effect of treatment on clinically relevant end-points. Studies of patients with community-acquired pneumonia have established certain expected rates of outcomes, including mortality, clinical complications, and time to resolution of symptoms. Recent studies have identified specific processes of care and treatment choices that have an impact upon these outcomes. However, there are no well-controlled studies that provide definitive estimates of the magnitude of the impact of antimicrobial therapy on these outcomes for patients with community-acquired pneumonia or other respiratory tract infections, such as acute exacerbations of chronic bronchitis. Most studies of the impact of drug resistance on outcomes for patients with respiratory tract infections have focused on the impact of beta-lactam drug resistance on outcomes for patients with community-acquired pneumococcal pneumonia. In general, these studies have demonstrated that outcomes are not affected by current levels of drug resistance, but most studies are hampered by small sample size, inability to control adequately for severity of illness and concordance of therapy, and inclusion of few subjects with high-level drug resistance. Additional studies are urgently needed to assess better whether the current empiric treatment guidelines are adequate or will need to be adjusted as patterns of resistance continue to evolve.