The impact of blood cultures on antibiotic therapy in pneumococcal pneumonia

Introduction: The cost-effectiveness of blood cultures in community- acquired pneumonia (CAP) has been questioned. Although penicillin-resistant Streptococcus pneumoniae is an increasing problem, penicillin therapy, where appropriate, reduces cost and may reduce antibiotic resistance. Blood cultures, however, can only reduce cost if physicians are prepared to alter therapy based on the results. We reviewed our experience to determine how often physicians changed management based on blood culture results positive for S pneumoniae. Methods: Retrospective chart review was performed of all CAP admissions between January 1996 and December 1998 with blood culture results positive for S pneumoniae. Results: Seventy-four patients out of 1,805 patients admitted with CAP during this period had pneumococcemia. Penicillin resistance was identified in 15 cases (20.3%; high grade in 4 cases) with cephalosporin resistance in 4 of these eases (1 high grade). Fifty-one patients had initial empiric therapy with a third-generation cephalosporin, and 58 patients had empiric coverage of atypical organisms; no patient received empiric penicillin therapy. Blood culture results altered management in 31 patients (41.9%), but in only 2 cases was this due to antibiotic resistance. Fifty-one patients without penicillin allergy grew penicillin-sensitive pneumococci; only 11 patients (21.6%) were changed to penicillin therapy. Thirteen of 35 patients (37.1%) who were given an additional antibiotic for atypical coverage had this antibiotic ceased. Conclusion: Despite evidence of penicillin-sensitive pneumococcal CAP, physicians were reluctant to narrow antibiotic therapy, potentially adding to treatment cost and reducing the impact of blood culture results on management. The impact of penicillin resistance was reduced by the usual empiric choice of a third-generation cephalosporin. While positive blood culture results can clearly be useful in the management of patients with CAP, their cost-effectiveness needs to be assessed in prospective clinical trials.