Penicillin resistance not a factor in outcome from invasive Streptococcus pneumoniae community-acquired pneumonia in adults when appropriate empiric therapy is started

Background. Invasive Streptococcus pneumoniae pneumonia among adults due to penicillin-resistant or intermediate resistant strains was investigated to determine whether these patients responded poorly to common antibiotic regimens compared to pneumonia due to susceptible strains. Methods: During a 21-year period (1983-2003), clinical outcome was analyzed among 3 groups of adults, 19 with resistant, 33 with intermediate, and 133 with susceptible invasive S pneumoniae pneumonia admitted to hospitals in Huntington, West Virginia. Adults with resistant and intermediate infections were matched by age and month of admission to a group of 133 adults with penicillin-susceptible infections. All isolates of resistant and intermediate infections were capsular serotypes/serogroups 6, 9, 14, 19, and 23, and isolates of susceptible infections included 24 different serotypes/serogroups. Case fatality rates were calculated for deaths that occurred during the first 7, first 14, and first 21 days of hospitalization. Minimal inhibitory concentration (MIC) was determined by E-test and capsular serotype by Quellung procedures. Results: The resistant and susceptible groups did not differ in several measures of severity of illness, including admission vital signs, duration of fever, mean total leukocyte count, number of lobes involved, preexisting underlying diseases, and antibiotic treatment regimens. There were no significant differences in case fatality rates between the 3 groups of pneumonia by days in hospital, age, severity of illness, and empiric antibiotic treatment regimen with a cephalosporin and a macrolide, the most common antibiotic regimen. Conclusions: These findings provide evidence that combination antibiotic regimens effective in the treatment of invasive susceptible S pneumoniae pneumonia are equally effective in the treatment of invasive resistant (MIC = 2-4 mu g/mL) and of intermediate (MIC = 0.1-1 mu g/mL) S pneumoniae pneumonia.