Incidence of penicillin-resistant streptococcus pneumoniae in Japan, 1993-1995

The Working Group for PRSP was organized through the participation of 40 institutions to investigate the incidence of penicillin (Pc)-resistant Streptococcus pneumoniae (PRSP) in Japan. We collected 2410 S. pneumoniae clinical isolates between October 1994 and March 1995. The susceptibility to Pc, erythromycin, and minocycline was determined by an agar dilution method using Mueller-Hinton agar supplemented with 5% sheep blood. Pc-susceptible S. pneumoniae (PSSP) were defined as bacteria for which the minimum inhibitory concentration (MIC) was ≤0.06μg/mL; Pc-intermediate S. pneumoniae (PISP) as those for which the MIC ranged from 0.125 to 0.25μg/mL; PRSP, as those with a MIC≥0.5μg/mL. The incidence of resistant strains including PISP and PRSP was 41.8% in 1994 and 40.8% in 1995. Logistic regression analysis showed that PRSP was significantly more frequent in infants aged 0 to 2 years old than in the general population and PSSP was significantly more frequent in elderly patients aged 60 or older. The rate of PRSP was significantly higher in the throat than in the sputum. Among 10 regions studied nationwide, PRSP was detected less frequently in the areas of Hokkaido and Hokuriku and more frequently in the areas of Chugoku, Shikoku, and Kyushu. Most PRSP were resistant to erythromycin and minocycline. PSSP serotyping using the capsule-quellung reaction indicated a number of types. In contrast, most PISP and PRSP were serotyped to types 19, 23, and 6.