Predicting Antimicrobial Resistance in Invasive Pneumococcal Infections

Background. The prevalence of multiantimicrobial resistance among Streptococcus pneumoniae continues to increase worldwide. In patients presenting with infection possibly due to pneumococci, recognition of risk factors that would identify those likely to have an antibiotic-resistant isolate might assist clinicians in choosing the most appropriate empirical therapy. Methods. A prospective cohort study of invasive pneumococcal infection was conducted in Toronto, Canada. Risk factors for antimicrobial resistance were evaluated by means of univariate and multivariate modeling. Results. A total of 3339 patients with invasive pneumococcal infection were identified between 1995 and 2002. Multivariate modeling revealed that risk factors for infection with penicillin-resistant as opposed to penicillin-susceptible pneumococci were year of infection (odds ratio [OR], 1.28; P < .001), absence of chronic organ system disease (OR, 1.72; P = .03), and previous use of penicillin (OR, 2.47; P = .006), trimethoprim-sulfamethoxazole (TMP-SMX; OR, 5.97; P < .001), and azithromycin (OR, 2.78; P = .05). Infection with TMP-SMX-resistant pneumococci was associated with absence of chronic organ system disease (OR, 1.64; P = .001) and with previous use of penicillin (OR, 1.71; P = .03), TMP-SMX (OR, 4.73; P < .001), and azithromycin (OR, 3.49; P = .001). Infection with macrolide-resistant isolates was associated with previous use of penicillin (OR, 1.77; P = .03), TMP-SMX (OR, 2.07; P = .04), clarithromycin (OR, 3.93; P < .001), and azithromycin (OR, 9.93; P < .001). Infection with fluoroquinolone-resistant pneumococci was associated with previous use of fluoroquinolones (OR, 12.1; P < .001), current residence in a nursing home (OR, 12.9; P < .001), and nosocomial acquisition of pneumococcal infection (OR, 9.94; P = .003). Conclusions. Knowledge of antimicrobial use during the 3 months before infection is crucial for determining appropriate therapy for a patient presenting to the hospital with an illness for which S. pneumoniae is a possible cause. Nosocomial acquisition and nursing home acquisition are significant risk factors for infection with fluoroquinolone-resistant pneumococci.