The impact of penicillin resistance on the outcome of invasive Streptococcus pneumoniae infection in children

Background: Invasive infections caused by Streptococcus pneumoniae with reduced susceptibility to penicillin are increasing in prevalence in Australia. Aims: To determine the impact of reduced susceptibility of S. pneumoniae to penicillin on morbidity, mortality and treatment of invasive infection. Methods: Retrospective case note review of children with invasive S. pneumoniae infection over a 26 month period. Penicillin minimum inhibitory concentrations (MIC) were determined by E test. Primary clinical outcome measures included days to defervescence, duration of hospital stay, complication rates and mortality. The secondary outcome of financial cost was examined. Comparisons between outcomes of patients with infections caused by susceptible and non-susceptible strains were performed with Student's t test, Pearson chi(2), Mann-Whitney U tests and multiple logistic regression. Results: Sixty-eight episodes of invasive pneumococcal disease were reviewed: 14 isolates (21.1%) had reduced susceptibility or resistance to penicillin (PNSSP, MIC 0.125 mg/L-1.5 mg/L). Ten patients had meningitis, 21 had pneumonia, 22 had bacteraemia with another focus and 15 had bacteraemia without an obvious focus. PNSSP were more common in patients with meningitis and pneumonia. No patients died. Overall, patients with infections caused by PNSSP had significantly longer hospitalisation and longer time to defervescence. Complication rates were not significantly different between groups. Outcome differences were no longer significant when meningitis patients were excluded from the analysis. The PNSSP group received more expensive intravenous antibiotics and their infections were significantly more costly to treat. Conclusions: Infections with penicillin non-susceptible S. pneumoniae are associated with higher morbidity than infections with penicillin susceptible strains, and treatment of these infections is more expensive, due to higher drug costs and longer hospital stay.