Surveillance based on molecular epidemiology for Haemophilus influenzae isolates between 1998 and 2000 in Japan

Results of clinical isolates collected by the Community-Acquired BacteriaI Infections Working Group

Abstract

The 6, 692 samples used in this study were sent to our laboratory by 187 medical institutions participating in the Community-Acquired Bacterial Infections Working Group between 1998 and 2000 in Japan. Acute otitis media (n=1, 425), acute upper respiratory tract infection (n=961), and acute bronchitis (n=390) were prevalent in 4, 030 cases, duplicates excluded. We also included 175 pneumonia cases in this study. The proportion of Haemophilus influenzae isolates in all cases was about 34%. The prevalence of H. influenzae isolates peaked in those aged 1 year and gradually decreased with age until children entered school. In contrast, average prevalence in adults was 10%. We conducted molecular-level epidemiological studies for 1, 408 strains using PCR to identify resistant genes in H. influenzae. Our 4 sets of primers are as follows:(i) p6 gene of p6 membrane protein, (ii) TEM-1 type β-lactamase gene (bla), (iii) normal PBP 3 gene (ftsI), and (iv) mutational ftsI gene detected in β-lactamase-nonproducing ampicillin (ABPC) resistant H. influenzae (BLNAR). H. influenzae strains were classified into 6 types based on PCR:(i)β-lactamase-nonproducing ABPC-susceptible strains (BLNAS; n=826) with no any resistant genes, (ii) TEM-1 type β-lactamase-producing ABPC resistant strains (BLPAR; n=81), (iii)β-lactamase-nonproducing and low-level ABPC-resistant strains (Low-BLNAR;n=352) possessing Asn -526→Lys-526 amino acid substitution, (iv) BLNAR strains (n: 109) possessing Asn-526→Lys-526 and 3 amino acids substitutions detected around the Ser-Ser-Asn conserved motif, (v)β-lactamase-producing amoxicillin-clavulanate resistant strains (BLPACR-I; n=36) possessing TEM-1 and Low-BLNAR resistant genes, and (vi)β-lactamase-producing amoxicillin-clavulanate resistant strains (BLPACR II: n=4) possessing TEM-1 and BLNAR resistant genes. ABPC MIC₉₀s in Low-BLNAR was 2μg/mL and in BLNAR was 8μg/mL. Susceptibility of oral and intravenous cephalosporins MICs to these resistant strains apparently decreased more than that of ABPC and meropenem. In oral cephalosporins, only cefditoren MIC₉₀ was excellent<1μg/mL against BLNAR. BLNAR increased significantly from 3.2% in 1998, 6.6% in 1999, and 13.5% in 2000. Insufficient serum concentrations after oral cephalosporins prescribed for immunological immature pediatric patients accelerate the increase of BLNAR strains. Selection of proper antibiotics based on rapid, accurate bacteriological examinations, and Hib vaccination against H. influenzae must be taken to prevent resistant microorganisms from increasing.