Apparent lower rates of streptococcal toxic shock syndrome and lower mortality in children with invasive group A streptococcal infections compared with adults.

Since 1985 there have been worldwide reports of increases in severe invasive Group A streptococcal (IGAS) infections. We reviewed the charts of all children with IGAS infections (defined as isolation of Group A streptococcus from a normally sterile site) presenting to our institution over a 7-year period (January, 1985, to December, 1991) and the literature. Streptococcal toxic shock syndrome required hypotension and multisystem organ involvement. Twenty-four patients (mean age, 4.96 +/- 4.4 years) were identified with IGAS infection. One patient (presenting in 1989) met the criteria for probable streptococcal toxic shock syndrome and none died. Eight of 19 Group A streptococcal isolates tested were streptococcal pyrogenic exotoxin (SPE) A producers, most (90%) had the speC gene and all had the speB gene and produced the toxin. No M or T type predominated. The low rates of streptococcal toxic shock syndrome and fatalities among children with IGAS infection are consistent with other pediatric but not with adult series. The apparent differences in outcome of IGAS between children and adults were not explained by the virulence factors we examined and may warrant further investigation.

Comparative activity of several antimicrobial agents against nosocomial Gram-negative rods isolated across Canada.

In 1992, a surveillance study was performed in Canada to determine the susceptibility of nosocomial Gram-negative rods to several wide spectrum antimicrobials. Consecutive isolates from 10 institutions, as well as additional strains of selected species of Enterobacteriaceae that are known to possess the Bush group 1 beta-lactamase, were tested for susceptibility to 12 antimicrobials. Third-generation cephalosporin resistance was found to be as high as 29% in Enterobacter cloacae that possesses the Bush group 1 beta-lactamase and less than 4% in those isolates not possessing this enzyme. Cefepime equalled or exceeded the activity of the third-generation cephalosporins against the species of Enterobacteriaceae that demonstrated resistance to the third-generation cephalosporins.

Epidemiological typing of Moraxella catarrhalis by pulsed field gel electrophoresis.

Pulsed field gel electrophoresis (pfge) was used to compare 59 strains of Moraxella catarrhalis to evaluate pfge for the epidemiological typing of this organism. pfge-generated patterns were compared with those obtained by small fragment restriction enzyme analysis (rea) and species-specific probe hybridization. The strains used in the study were isolated from various geographic locations and included proven epidemiologically related strains. pfge yielded more unique patterns than dna-dna hybridization - 30 versus 18, respectively - but fewer than rea, which generated 45 unique patterns. Strains that demonstrated the same rea pattern or dna-dna hybridization pattern did not always demonstrate the same pfge pattern. For example, in 23 epidemiologically unrelated strains that shared six rea patterns, pfge differentiated the isolates into 12 patterns. Conversely, strains that demonstrated the same pfge pattern did not always demonstrate the same rea pattern or hybridization pattern. For example, in 42 strains that shared 13 pfge patterns, rea differentiated the isolates into 31 patterns and dna-dna hybridization differentiated them into 16 patterns. However, compared with rea, pfge yielded less complex patterns that were more easily comparable, and compared with dna-dna hybridization, pfge was technically easier.

Canadian survey of antimicrobial resistance in Klebsiella spp. and Enterobacter spp. The Canadian Antimicrobial Resistance Study Group.

Increasing antimicrobial resistance has been reported for Klebsiella spp. and Enterobacter spp. The in-vitro activities of 14 antimicrobial agents against 656 clinical isolates of Klebsiella spp. and 630 isolates of Enterobacter spp. collected from seven cities in Canada were determined by microbroth dilution. There was no regional variation in the susceptibility patterns. Klebsiella spp. remain highly susceptible to most antimicrobials, only one isolate was resistant to third-generation cephalosporins. However, many isolates of Enterobacter spp. (> 16%) were resistant to the third-generation cephalosporins with marked cross-resistance to piperacillin (63.1%), piperacillin/tazobactam (44.9%), and aztreonam (76.6%). Gentamicin, tobramycin, imipenem, ciprofloxacin, cefepime, and cefpirome were consistently active against most isolates of Enterobacter spp. including those resistant to the third-generation cephalosporins.

Comparative in vitro activity of cefdinir (CI-983; FK-482) against staphylococci, gram-negative bacilli and respiratory tract pathogens.

The in vitro activity of cefdinir (CI-983; FK-482), a new oral cephalosporin, was compared with that of other antimicrobial agents against clinical isolates of staphylococci, gram-negative bacilli and common respiratory tract pathogens. Cefdinir (MIC90 less than or equal to 2.0 micrograms/ml) was more active than cefixime (MIC90 greater than 64 micrograms/ml) and equally as active as cefuroxime (MIC90 2.0 micrograms/ml) against oxacillin-susceptible staphylococci. Cefdinir was active against Haemophilus influenzae, including beta-lactamase producers (MIC90 0.5 microgram/ml), Moraxella catarrhalis (MIC90 less than or equal to 0.12 microgram/ml), Streptococcus pneumoniae (MIC90 less than or equal to 0.06 microgram/ml) and Streptococcus pyogenes (MIC90 less than or equal to 0.06 microgram/ml). The activity of cefdinir against gram-negative bacilli was variable; organisms with chromosomal cephalosporinases were often resistant.

Community-acquired pneumonia: the future of the microbiology laboratory: focused diagnosis or syndromic management?

The traditional classification of community-acquired pneumonia into typical and atypical pneumonia to facilitate successful empirical treatment is no longer optimal. An accurate prediction of cause and adequate empirical therapy cannot be provided with this approach in severely ill patients. There is an increasing spectrum of recognized treatable pathogens presenting as community-acquired pneumonia including Legionella species, Chlamydia pneumoniae, and Pneumocystis carinii in addition to the traditional community pathogens. The variability of presentation in severely ill or compromised hosts makes clinical prediction of cause inadequate. A more rational approach may involve the classification of patients by the severity of illness and underlying disease with little or no microbiological workup in mild illness unless the results will contribute to the epidemiological surveillance of resistance because these investigations have not been shown to affect outcome in this setting. Etiologic diagnosis should be more aggressively sought and the microbiology laboratory can be best used by providing the efficient and rapid diagnosis of this expanded range of pathogens in more severely ill patients. The mounting antimicrobial resistance of common pathogens such as Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus will require not only a critical review of empirical therapy, but an increased emphasis on epidemiological monitoring of resistance by laboratories and effective communication with clinicians.

Broth microdilution testing of Haemophilus influenzae with haemophilus test medium versus lysed horse blood broth. Canadian Haemophilus Study Group.

Broth microdilution testing of 702 community-acquired isolates of Haemophilus influenzae from across Canada was performed with both Mueller-Hinton broth supplemented with 3% lysed horse blood broth (LHB) (BBL Microbiology Systems, Cockeysville, Md.) and haemophilus test medium (HTM). The prevalence of beta-lactamase production was found to be 26% with no regional variation. MICs determined with LHB tended to be higher than those with HTM, but interpretive errors due to these differences were observed only rarely with trimethoprim-sulfamethoxazole (n = 5), cefaclor (n = 8), and cefamandole (n = 3). The interobserver variability in MIC determinations was found to be greater when LHB was used than when HTM was used. There was no difference in intraobserver variability between the two medium formulations. beta-Lactamase-positive isolates developed false resistance to amoxicillin-clavulanate 2 weeks after microdilution panels of both types of medium were stored at -20 degrees C but not when panels were stored at -70 degrees C. In conclusion, this study supports the use of HTM rather than LHB for sensitivity testing of H. influenzae because of its lower rate of interobserver variability and its ability to support the growth of these organisms, which is comparable to that of LHB.

Surveillance of susceptibility testing methodologies for Haemophilus influenzae in Canada, including evaluation of disk diffusion test.

We surveyed 75 clinical laboratories to determine if National Committee for Clinical Laboratory Standards (NCCLS) were being used for the susceptibility testing of Haemophilus influenzae. Of the 66 laboratories that performed susceptibility testing, all claimed to follow current NCCLS guidelines. However, upon further questioning, only 23, all of which used disk diffusion testing, accurately interpreted and followed the guidelines. Proficiency testing of 22 of these laboratories found that an unacceptable number of interpretive errors (> 10%) occurred. These results query the merit of routine disk diffusion susceptibility testing of H. influenzae to beta-lactam agents.

Detection of vancomycin resistance in Enterococcus species.

Enterococcus faecalis and Enterococcus faecium isolates that are resistant to vancomycin have recently been identified in North America and Europe. Of 155 clinical isolates of enterococci (113 E. faecium and 42 E. faecalis), we found that 98 were resistant, 52 were moderately susceptible, and 5 had intermediate susceptibilities to vancomycin by using broth microdilution susceptibility testing according to the National Committee for Clinical Laboratory Standards (NCCLS) (Approved Standard M7-A2). Using NCCLS disk diffusion methodology (Approved Standard M2-A4), we evaluated the NCCLS supplemental M100-S3 revisions for zone diameter interpretive standards and incubation conditions and found 5.8% minor errors. A total of 234 isolates, which included an additional 79 E. faecium isolates that were moderately susceptible to vancomycin, were used to evaluate the Vitek GPS-TA card (bioMerieux, Inc., Hazelwood, Mo.) and the Pos MIC type 6 panel (MicroScan; Baxter Health Care Corp., West Sacramento, Calif.) for the detection of vancomycin resistance. The Vitek card was 100% specific and 72% sensitive, whereas the MicroScan panel with the Walk/Away system was 98% specific, with a sensitivity of 93% which increased to 99% when readings were performed manually. An agar screen plate method was evaluated with vancomycin concentrations of 6, 8, 10, or 12 micrograms/ml; plates were inoculated so as to obtain a final concentration of 10(5) CFU per spot. This method was found to be 100% sensitive and specific at all concentrations.

Determination of antimicrobial susceptibilities of Canadian isolates of Haemophilus influenzae and characterization of their beta-lactamases. Canadian Haemophilus Study Group.

Susceptibility testing of 1,688 Haemophilus influenzae isolates found 484 ampicillin-resistant strains; 474 strains (28.4%) were beta-lactamase positive, and 5 strains (0.4%) were non-beta-lactamase producers. Restriction enzyme digestion of the beta-lactamase amplicon determined that, of 157 strains, 11 (7.0%) contained ROB-1 beta-lactamase and 146 (93.0%) contained a TEM-type beta-lactamase.