Increasing frequency of penicillin-resistant pneumococci: Epidemiological aspects and case-control study

At the Hadassah University Hospital, Mt. Scopus, Jerusalem, the frequency of patients with relatively penicillin-resistant pneumococci (RPRP) isolates has increased from 0.9 to 10.8% during the years 1979-82. Infants and children were particularly involved. Significantly more RPRP isolates were found in those < 14 years old than in those who were older (P < 0.005). The determination of susceptibility or relative resistance to penicillin was based on the disk sensitivity method, which remained unchanged throughout the study period. The minimal inhibitory concentration (MIC) to penicillin G was also determined for 20 RPRP isolates and was found to be in the range of relative resistance to penicillin (0.25 to 0.50 μg/ml) in all 20 isolates. A case-control study of 16 index patients examined antibiotic usage during the 60 days preceding pneumococcal isolation. Total antibiotic usage was high in both groups (18.8 vs. 8.8 days, P = 0.2); β-lactam antibiotic usage was significantly higher in the RPRP group than in the control group (13.3 vs. 4.2 days, 0.01 < P < 0.02). General prescribing practices, even in non-isolated areas where there is no need for public health programs to dispense prophylactic antibiotics, may produce sufficiently high antibiotic exposures to aid the emergence of RPRP strains.