Clinical significance of pneumococcal resistance and factors influencing outcomes.

Despite increasing penicillin and macrolide resistance worldwide, the clinical relevance of this phenomenon is still unknown. Debate continues as to whether increasing resistance among pneumococci to beta-lactam agents, macrolides, and fluoroquinolones has been accompanied by an increase in the rate of treatment failure. In vitro findings do not appear to be predictive of in vivo outcomes. Studies have failed to demonstrate significantly higher mortality for patients infected with penicillin-resistant rather than penicillin susceptible pneumococcal strains. Treatment failures are associated solely with the highest levels of resistance. Antimicrobial resistance appears to affect other markers of morbidity, but only statistically nonsignificant trends toward increased mortality have been demonstrated. Whether macrolide resistance among invasive pneumococcal isolates is clinically relevant or a matter of limited influence remains to be determined.