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The "HACEK" organisms are a group of fastidious Gram-negative bacteria that cause a variety of infections, including infective endocarditis. Antimicrobial susceptibility testing is not universally available, and therapy for these infections is often empirical. We report the antimicrobial susceptibilities of 70 clinical HACEK isolates to 18 antimicrobials. All isolates were susceptible to ceftriaxone and levofloxacin, indicating that these agents remain appropriate empirical choices for the treatment of infections with this group of organisms. The "HACEK" group of fastidious Gram-negative organisms includes Haemophilus species (other than Haemophilus influenzae), Aggregatibacter actinomycetemcomitans (formerly Actinobacillus actinomycetemcomitans), Aggregatibacter aphrophilus (formerly Haemophilus aphrophilus), Cardiobacterium hominis, Eikenella corrodens, and Kingella kingae. These organisms are normal flora of the human oral cavity, but are capable of causing disease, most notably infective endocarditis (IE), but also periodontal infections, abscesses, and nonendocarditis bacteremia secondary to focal infections.Since these organisms are fastidious, antimicrobial susceptibility testing is often difficult and impractical, particularly for primary/non-reference laboratories. Therefore, therapy is often chosen empirically based on published reports and guidelines.North American and European IE guidelines recognize that the likelihood of ampicillin resistance in HACEK organisms precludes empirical therapy with ampicillin (1-3). The recommended treatment of IE due to these organisms is therefore a broad-spectrum cephalosporin or a fluoroquinolone. This is based on limited data due to the clinical rarity of infections by these organisms. To our knowledge, only one study has described the antimicrobial susceptibilities of multiple genera of HACEK organisms, which included 42 clinical and American Type Culture Collection (ATCC) strains (4).The Public Health Ontario Laboratory-Toronto (PHOL) is a provincial reference laboratory for antimicrobial susceptibility testing in the province of Ontario, Canada, with a catchment area of 13.5 million people. HACEK organisms are sent to this laboratory from primary, tertiary, and quaternary care centers for identification and/or susceptibility testing. From January 2010 to July 2012, PHOL received 241 HACEK isolates for identification and/or susceptibility testing. Of those, 49 isolates were submitted for identification only and 18 isolates were recovered from autopsy specimens, which do not routinely undergo susceptibility testing. The remaining 174 isolates were submitted for identification and susceptibility testing. Isolates were identified using either traditional biochemical tests or the 16S rRNA molecular assay (5). Antimicrobial susceptibility testing was performed using broth microdilution with cation-adjusted Mueller-Hinton broth (CAMHB) containing 5% (vol/vol) lysed horse blood (LHB) per Clinical and Laboratory Standards Institute (CLSI) M45-A2 guidelines (6). After 48 ...

BackgroundInvasive meningococcal disease (IMD) caused by serogroup B is the last major serogroup in Canada to become vaccine-preventable. The anticipated availability of vaccines targeting this serogroup prompted an assessment of the epidemiology of serogroup B disease in Ontario, Canada.MethodsWe retrieved information on confirmed IMD cases reported to Ontario’s reportable disease database between January 1, 2000 and December 31, 2010 and probabilistically-linked these cases to Public Health Ontario Laboratory records. Rates were calculated with denominator data obtained from Statistics Canada. We calculated a crude number needed to vaccinate using the inverse of the infant (<1 year) age-specific incidence multiplied by expected vaccine efficacies between 70% and 80%, and assuming only direct protection (no herd effects).ResultsA total of 259 serogroup B IMD cases were identified in Ontario over the 11-year period. Serogroup B was the most common cause of IMD. Incidence ranged from 0.11 to 0.27/100,000/year, and fluctuated over time. Cases ranged in age from 13 days to 101 years; 21.4% occurred in infants, of which 72.7% were <6 months. Infants had the highest incidence (3.70/100,000). Case-fatality ratio was 10.7% overall. If we assume that all infant cases would be preventable by vaccination, we would need to vaccinate between 33,784 and 38,610 infants to prevent one case of disease.ConclusionsAlthough rare, the proportion of IMD caused by serogroup B has increased and currently causes most IMD in Ontario, with infants having the highest risk of disease. Although serogroup B meningococcal vaccines are highly anticipated, our findings suggest that decisions regarding publicly funding serogroup B meningococcal vaccines will be difficult and may not be based on disease burden alone.