Medical outcomes and antimicrobial costs with the use of the American Thoracic Society guidelines for outpatients with community-acquired pneumonia.

CONTEXT: The American Thoracic Society (ATS) published guidelines based on expert opinion and published data--but not clinically derived or validated--for treating adult outpatients with community-acquired pneumonia.

OBJECTIVE: To compare medical outcomes and antimicrobial costs for patients whose antimicrobial therapy was consistent or inconsistent with ATS guidelines.

DESIGN: Multicenter, prospective cohort study.

SETTING: Emergency departments, medical clinics, and practitioner offices affiliated with 3 university hospitals, 1 community teaching hospital, and 1 health maintenance organization.

PARTICIPANTS: A total of 864 immunocompetent, adult outpatients with community-acquired pneumonia: 546 aged 60 years or younger with no comorbidity and 318 older than 60 years or with 1 comorbidity or more.

MAIN OUTCOME MEASURES: Patients' antimicrobial therapy was classified as being consistent or inconsistent with the ATS guidelines. Mortality, subsequent hospitalization, medical complications, symptom resolution, return to work and usual activities, health-related quality of life, and antimicrobial costs were compared among those treated consistently or inconsistently with the guidelines.

RESULTS: Outpatients aged 60 years or younger with no comorbidity who were prescribed therapy consistent with ATS guidelines (ie, erythromycin with some exceptions) had 3-fold lower antimicrobial costs ($5.43 vs $18.51; P<.001) and no significant differences in medical outcomes. Outpatients older than 60 years or with 1 comorbidity or more who were prescribed therapy consistent with ATS guidelines (ie, second-generation cephalosporin, sulfamethoxazole-trimethoprim, or beta-lactam and beta-lactamase inhibitor with or without a macrolide) had 10-fold higher antimicrobial costs ($73.50 vs $7.50; P<.001); despite trends toward higher mortality and subsequent hospitalization, no significant differences in medical outcomes were observed.

CONCLUSION: Our findings support the use of erythromycin as recommended by the ATS guidelines for outpatients aged 60 years or younger with no comorbidity. Although the antimicrobial therapy recommended in outpatients older than 60 years or with 1 comorbidity or more is more costly, this observational study provides no evidence of improved medical outcomes in the small subgroup who received ATS guideline-recommended therapy.