Treatment of Outpatient Community-Acquired Pneumonia: Risk Factors for Drug-Resistant Streptococcus pneumoniae and Effect on Antibiotic Selection

Background: Increased fluoroquinolone use has been associated with the development of resistance.  Judicious use of this important drug class is critical to slow the emergence of further resistance.  The Infectious Diseases Society of America (IDSA) guideline for the management of community-acquired pneumonia (CAP) recommends a respiratory fluoroquinolone for the outpatient treatment of CAP in patients who have risk factors for drug-resistant Streptococcus pneumoniae (DRSP).  

Objective:  To assess risk factors for DRSP, antimicrobial choices, and clinical outcomes in patients with outpatient CAP in relation to IDSA guideline recommendations.

Methods:  We performed a retrospective cohort study of adults discharged from our emergency department or urgent care center with a primary ICD-9 diagnosis of pneumonia from April 2009 through October 2009.   Analyses were stratified according to the presence of risk factors for DRSP as specified in the IDSA guideline. Outcomes including treatment failure, recurrent infection, hospitalization for pulmonary infection, and mortality were assessed during a 30-day follow-up period.   

Results:  175 patients were treated for pneumonia; however, only 114 (65%) met objective criteria for CAP.  Of the 175 patients, current tobacco use (79, 42%), asthma (28, 16%), alcohol abuse (24, 14%), diabetes mellitus (18, 10%), use of a proton pump inhibitor (20, 11%), and chronic obstructive pulmonary diseases (16, 9%) were the most common risk factors for pneumonia.  68 (39%) patients met at least one criteria for DRSP, most commonly COPD (16, 9%), alcohol abuse (24, 14%), diabetes mellitus (18, 10%), and antibiotic usage within 90 days (15, 9%).  There were no significant differences in antimicrobial choices for patients with and without risk factors for DRSP (table). 

Antimicrobial choice	No risk for DRSP n = 107	Risk factor for       DRSP present         n = 68	P
Azithromycin	68 (64%)	36 (53%)	0.16
Doxycycline	29 (27%)	19 (28%)	0.90
Levofloxacin	9 (8%)	9 (13%)	0.31
β-lactam	2 (2%)	2 (3%)	0.64
Other	0 (0%)	3 (4%)	0.06

Nine (5%) patients experienced treatment failure (5, 3%) or recurrence of infection (5, 3%).  Severe adverse events including hospitalization for pulmonary infection (2, 2% vs. 4, 6%, p = 0.21) and death (0, 0% vs. 0, 0%) were uncommon in patients with and without risk factors for DRSP, respectively.   

Conclusions:  Risk factors for DRSP in patients treated for outpatient CAP are common; however, the presence of these risk factors did not significantly alter antimicrobial choices.  Despite this, severe adverse outcomes were uncommon.  Whether the use of fluoroquinolones is justified by improved outcomes is an important question that requires further study.