Influence of penicillin resistance on outcome in adult patients with invasive pneumococcal pneumonia:: is penicillin useful against intermediately resistant strains?

Objectives: To compare outcome between patients with pneumonia due to penicillin-susceptible S. pneumoniae and patients with pneumonia due to penicillin intermediately resistant strains and to study the outcome of patients with pneumococcal pneumonia caused by strains with MICs of 0.12-1 mg/L treated empirically during the first 48 h with beta-lactam antibiotics. Materials and methods: We studied 247 adult patients with invasive pneumococcal pneumonia occurring from 1997 to 2001. The following data were recorded from each patient: socio-demographic characteristics, underlying diseases, clinical presentation, initial severity of pneumonia, initial and subsequent antimicrobial therapy, in-hospital complications, hospital mortality and length of hospital stay. Multivariate analysis was done to identify variables associated with the development of pneumonia caused by a non-susceptible strain. Results: The overall presence of penicillin non-susceptibility was 26.7%; no strain had an MIC >2 mg/L. Overall mortality was 23.5% in patients with pneumonia caused by intermediately resistant pneumococci and 12.7% in those with pneumonia caused by susceptible strains (P=0.075). Mortality during the first 7 days of admission, considered to be pneumonia-related deaths (13.7% versus 9.9%; P=0.448) was similar in both groups. The multivariate analysis showed that serotype 14 (OR, 140.18; 95% CI, 16.95-1159.20), serotype 19 (OR, 7.53; 95% CI, 1.98-28.7), haematological malignancy or splenectomy (OR, 4.46; 95% CI, 1.5-13.23) and HIV infection (OR, 4.54; 95% CI, 1.54-13.44) were the only independent factors associated with pneumonia caused by penicillin intermediately resistant pneumococci. In patients with strains having MICs of 0.1-1 mg/L, overall mortality was similar in the group of penicillin-treated patients (22.2%) to those treated with broad-spectrum beta-lactams (23.5%). Conclusions: There is a non-significant trend to higher mortality in patients with pneumococcal pneumonia caused by intermediately resistant strains; however, they do not have a poorer outcome when they are treated with amoxicillin.