Antimicrobial susceptibility of pathogens isolated from more than 10,000 patients with infectious respiratory diseases: a 25-year longitudinal study.

The Study Group on Antimicrobial Susceptibility of Pathogens Isolated from Respiratory Infections was established in 1981 in Japan to elucidate trends in such susceptibilities in patients with infectious respiratory diseases; the Group has conducted nationwide research in collaboration with 21 medical institutions. Examination of more than 10,000 patients by 2005 allowed a summary of study findings. Streptococcus pneumoniae started to become resistant to penicillin G in the 1990s, and the isolation rate of penicillin-intermediate and penicillin-resistant S. pneumoniae (PISP + PRSP) reached almost 60% in 2001. The proportion of PRSP also increased, reaching 19.4%. Thereafter, the rate of PISP + PRSP decreased somewhat to the mid-30% range. Macrolide resistance was also observed; in 2005, the prevalence of strains highly susceptible to erythromycin with MICs <or= 0.06 microg/ml had decreased to 15.5%, whereas the proportion of highly resistant strains with MICs >or= 128 microg/ml exceeded 40%. Among Staphylococcus aureus isolates, the proportion of methicillin-resistant S. aureus (MRSA) strains began to increase rapidly in 1986 and constituted around 60% of all S. aureus strains identified in 1990 and in the following years. In 1993, the prevalence of ampicillin-resistant isolates of Haemophilus influenzae had increased remarkably, presumably related to the outbreak of beta-lactamase-negative ampicillin-resistant (BLNAR) H. influenzae strains, and the proportion of these strains among the isolates surpassed 30% in 2002 and thereafter. For Klebsiella pneumoniae, the antimicrobial activity of first- to fourth-generation cephems improved with each generation. The MIC distribution patterns of Pseudomonas aeruginosa shifted towards higher MICs when compared with the MICs for other pathogens. Broad patterns with no distinct peaks reflected the difficulty in treating P. aeruginosa infection. Regarding Moraxella catarrhalis, beta-lactamase-producing strains already constituted a majority of the isolates in 1990, and the proportion of strains highly susceptible to ampicillin, with MICs <or= 0.06 microg/ml, was less than 10% at that time.