Direct isolation of Francisella spp. from environmental samples.

AIMS: To develop a selective medium for isolation of F. tularensis, F. novicida and F. philomiragia from environmental samples. METHODS AND RESULTS: A selective media, cysteine heart agar with 9% chocolatized sheep blood, containing polymyxin B, amphotericin B, cyclohexamide, cefepime and vancomycin (CHAB-PACCV) was developed and evaluated for growth of Francisella spp. No differences were observed in recovered colony forming units (CFUs) for F. tularensis, F. novicida and F. philomiragia on CHAB-PACCV vs nonselective CHAB. Growth of non-Francisella species was inhibited on CHAB-PACCV. When environmental samples were cultured on CHAB and CHAB-PACCV, only CHAB-PACCV allowed isolation of Francisella spp. Three new Francisella strains were isolated directly from seawater and seaweed samples by culture on CHAB-PACCV. CONCLUSIONS: CHAB-PACCV can be used for direct isolation of Francisella spp from environmental samples. SIGNIFICANCE AND IMPACT OF THE STUDY: Francisella spp. show a close association with environmental sources. Future utilization of CHAB-PACCV for isolation of Francisella spp. directly from environmental samples should prove valuable for investigating outbreaks and human infections attributed to environmental exposure.

Prospective study of 125 cases of Staphylococcus aureus bacteremia in children in New Zealand.

BACKGROUND: Staphylococcus aureus bacteremia is a common complication of S. aureus infection. There are few pediatric studies defining the incidence and associated morbidity and mortality of S. aureus bacteremia and no such New Zealand studies. We conducted a prospective study of S. aureus bacteremia in children in New Zealand. METHODS: From July 1, 1996 to December 31, 1998, we included all children < 16 years of age with S. aureus bacteremia in Auckland and Christchurch. Relevant information regarding patient demographics, clinical course and outcome and laboratory results was recorded. RESULTS: One hundred twenty-five cases of true S. aureus bacteremia were identified. There were 4 deaths within 30 days of the onset of bacteremia. Fourteen (11%) of the children were < 1 month of age. Maori children (relative risk, 2.0; 95% confidence interval, 1.3 to 3.2) were twice as likely and Pacific Island children (relative risk, 2.5; 95% confidence interval, 1.6 to 3.8) 2.5 times as likely as white children to acquire S. aureus bacteremia. The peak incidence of S. aureus bacteremia was observed in Pacific Island children < 1 year of age (105 cases/100,000 children/year). Twenty-seven percent of cases were related to intravenous catheters. Seventy percent of cases were community-acquired. Ninety-eight percent of non-catheter-related cases in children > 1 month of age were community-acquired. There was a low rate of methicillin resistance (6%). CONCLUSIONS: S. aureus bacteremia is largely community-acquired in children in New Zealand and is more common in Pacific Island and Maori populations. Although there is a low associated mortality, a significant number are potentially preventable cases secondary to intravenous catheters.

Prospective study of 424 cases of Staphylococcus aureus bacteraemia: determination of factors affecting incidence and mortality.

BACKGROUND: Staphylococcus aureus bacteraemia (SAB) is a common complication of S. aureus infection and is associated with a high mortality. AIMS: To document prospectively the pattern of illness associated with SAB in New Zealand and, by recording patient demographic factors and clinical features, to identify risk factors associated with a poor outcome. METHODS: From 1 July 1996 to 31 December 1997, adults with SAB were prospectively studied in six tertiary care hospitals. All information obtained from patients' records was recorded on worksheets and transferred to a computerized spreadsheet for analysis. RESULTS: There were 424 patients with SAB. Maori (relative risk (RR)= 1.8, 95% confidence interval (CI) = 1.3-2.6) and Pacific Island people (RR = 4.0, 95% CI = 3.1-5.3) were significantly more likely than people of European descent to acquire SAB, but not to die from the infection. Fifty per cent of cases were community acquired. A source was identified for 85%: intravenous catheter (31%), primarily hospital acquired, and skin/soft tissue (22%), primarily community acquired, were the most common foci. The 30-day mortality was 19%, 83% of whom died within 2 weeks. Risk factors for a poor outcome were: increasing age above 60, female sex (RR = 1.4, 95% CI = 1.0-2.1), diabetes mellitus (RR = 1.5, 95% CI = 1.0-2.4), immunosuppression (RR = 1.5, 95% CI = 1.0-2.4), pre-existing renal impairment (RR = 1.8, 95% CI = 1.2-2.7), malignancy (RR= 2.2, 95% CI = 1.4-3.5), lung as a source (RR = 2.8, 95% CI = 1.9-4.2) and unknown source (RR = 2.3, 95% CI = 1.5-3.3). Mortality was also accurately predicted by two multifactor scoring systems. There was a low rate of methicillin resistance (5%). CONCLUSIONS: Staphylococcus aureus bacteraemia is more likely to occur in certain ethnic groups, while mortality is associated with other identifiable risk factors and continues to be high. Intravenous catheters remain the most common and most preventable cause of SAB.

A comparison of seven tests for serological diagnosis of tuberculosis.

Seven serological tests, two immunochromatographic tests, ICT Tuberculosis and RAPID TEST TB, and five enzyme-linked immunosorbent assays, TUBERCULOSIS IgA EIA, PATHOZYME-TB complex, PATHOZYME-MYCO IgG, PATHOZYME-MYCO IgA, and PATHOZYME-MYCO IgM, were evaluated simultaneously with 298 serum samples from three groups of individuals: 44 patients with active tuberculosis, 204 controls who had undergone the Mantoux test (89 Mantoux test-positive and 115 Mantoux test-negative controls), and 50 anonymous controls. The sensitivities of the tests with sera from patients with active tuberculosis were poor to modest, ranging from 16 to 57%. All the tests performed equally with sera from subgroups of those with active tuberculosis, those with pulmonary (33 patients) versus extrapulmonary (11 patients) disease, and those who were smear positive (24 patients) versus smear negative (12 patients) (P > 0.05). The specificities of the tests ranged from 80 to 97% with sera from the Mantoux test controls and 62 to 100% with sera from the anonymous controls. The TUBERCULOSIS IgA EIA had the highest sensitivity (57%) with sera from patients with active tuberculosis, with a high specificity of 93% with sera from the Mantoux test controls, but a very poor specificity of 62% with sera from the anonymous controls. Overall, ICT Tuberculosis followed by PATHOZYME-MYCO IgG had the best performance characteristics, with sensitivities of 41 and 55%, respectively, with sera from patients with active tuberculosis and specificities of 96 and 89%, respectively, with sera from the Mantoux test controls and 88 and 90%, respectively, with sera from the anonymous controls. By combining all the test results, a maximum sensitivity of 84% was obtained, with reciprocal drops in specificities to 55 and 42% for the Mantoux test controls and anonymous controls, respectively. The best combination was that of ICT Tuberculosis and PATHOZYME-MYCO IgG, with a sensitivity of 66% and a specificity of 86% for the Mantoux test controls and a sensitivity and specificity of 78% for the anonymous controls. While a negative result by any one of these tests would be useful in helping to exclude disease in a population with a low prevalence of tuberculosis, a positive result may aid in clinical decision making when applied to symptomatic patients being evaluated for active tuberculosis.

Prospective vancomycin audit in Auckland healthcare hospitals.

AIM: In response to emerging vancomycin resistance among gram-positive cocci, it is recommended that hospitals develop guidelines for the appropriate use of glycopeptides and identify situations where glycopeptide use should be discouraged. The aim of this study was to audit the use of vancomycin in Auckland Healthcare hospitals. METHOD: Patients prescribed vancomycin were recorded by pharmacy staff at Auckland, Starship, Green Lane and National Women's Hospitals. Clinical and laboratory information was collected for each course of vancomycin treatment. Standard definitions were used to classify prophylactic, empirical or specific directed therapy as appropriate or inappropriate. Continuing vancomycin when cultures were negative for beta-lactam-resistant, gram-positive organisms and/or initial choice of vancomycin when it was not necessary for the presumed source of infection were reasons for inappropriate empirical use. Reasons for inappropriate specific directed therapy included vancomycin prescribed for methicillin susceptible S. aureus and coagulase-negative staphylococci, or penicillin susceptible viridans streptococci when there was no history of beta-lactam allergy. RESULTS: One hundred and sixty-eight courses of vancomycin were prescribed for 146 patients; 42 in children (<16 years) and 126 in adults. Thirty-two per cent of all vancomycin courses were in renal patients, 26% in surgical specialities, 17% in haematology/oncology patients, 14% in medical specialities and 10% in intensive care unit patients. Eighty-six (51%) courses of vancomycin were considered inappropriate. The majority, 54/86 (63%) of inappropriate use, was for empirical therapy. It was an inappropriate initial choice in 25 instances, the duration of treatment was inappropriate, given no beta-lactam-resistant organisms were isolated in nine instances and both its initial choice and duration were inappropriate in 20 instances. Switching to other antimicrobial agents sooner when culture results and susceptibilities became available would have shortened the duration of 58/86 (67%) of the inappropriate courses. Of the inappropriate courses, 44/86 (51%) were prescribed for renal patients, 22 for empirical use, e.g. for peritoneal dialysis-related peritonitis, wound infections and presumed line infections and 22 for specific therapy of beta-lactam susceptible isolates because of dosing convenience in patients with renal failure. CONCLUSION: Half of the vancomycin use in Auckland Healthcare hospitals could potentially be modified. The majority of inappropriate use (63%) was for empirical therapy. The microbiology laboratory's ability to promptly and accurately report culture and susceptibility results and convey these to the prescribing clinician is important in reducing unnecessary doses. This study identified areas where interventions will be focused to reduce vancomycin use.

Evaluation of the tuberculin gamma interferon assay: potential to replace the Mantoux skin test.

We evaluated an in vitro test of cell-mediated immunity, the tuberculin gamma interferon assay, QuantiFERON-TB (QIFN), in 455 individuals from three groups: group I, 237 immigrants from high-risk countries; group II, 127 health care workers undergoing Mantoux testing; group III, 91 patients being investigated for possible active tuberculosis (79 patients) or Mycobacterium avium-Mycobacterium intracellulare complex infection (12 patients). The QIFN results were compared either to those of the Mantoux test or to microbiological and clinical diagnosis, as appropriate. In each group the correlation between the diameter of induration for the skin test and the magnitude of QIFN response was significant and of moderate strength (Spearman's rank correlation coefficient; rho = 0.59 to 0.61; P < 0.001). For group I, the agreement between QIFN and Mantoux results was 89% for Mantoux-negative and 64% for Mantoux-positive individuals. For group II, when >/=10-mm-diameter induration was taken as positive, the agreement was 81% for Mantoux-negative and 67% for Mantoux-positive individuals. For group III, agreement was 81% for Mantoux-negative and 86% for Mantoux-positive patients. For patients being evaluated for active tuberculosis, the performance of the Mantoux test was not statistically different from that of the QIFN assay. In patients with active tuberculosis, the assay had a sensitivity of 77%, not significantly higher for extrapulmonary than pulmonary cases (83% versus 74%). QIFN sensitivity was not significantly different for smear-negative or smear-positive cases (80% versus 71%). The QIFN assay is a potential replacement for the Mantoux test. The acceptability of these performance values and those of similar evaluations will determine the place this test will have in detecting evidence of mycobacterial infection.

Susceptibility of anaerobic bacteria in Auckland: 1991-1996.

AIM: To determine the antimicrobial susceptibility of local anaerobic bacteria. METHOD: The antimicrobial susceptibility of 357 obligate anaerobes collected between 1991 and 1997 was determined by a standard agar dilution method. Isolates tested included Bacteroides spp. 131, Fusobacterium spp. 12, Prevotella spp. 13, Veillonella spp. 5, Clostridium perfringens 27, other Clostridium spp. 29, Propionibacterium spp. 57, Actinomyces spp. 7, other non-sporing gram-positive bacilli 28 and Peptostreptococcus spp. 48. Ten antimicrobials were tested: penicillin, amoxycillin/ clavulanic acid, pipercillin/tazobactam, ceftriaxone, cefoxitin, cefotetan, imipenem, meropenem, clindamycin and metronidazole. RESULTS: Imipenem, pipercillin/tazobactam, meropenem and amoxycillin/clavulanic acid were active against virtually all anaerobes tested. Metronidazole was active against all anaerobic gram-negative bacteria and Clostridium spp., but had variable activity against other anaerobes. Cefoxitin was the most active cephalosporin against Bacteroides spp., with 76%, 64% and 15% of Bacteroides spp. being susceptible to cefoxitin, cefotetan and ceftriaxone, respectively. Penicillin had poor activity against anaerobic gram negative bacilli. Actinomyces and Propionibacterium spp. were susceptible to all antimicrobials tested except metronidazole. Variable results were obtained with other antimicrobial-organism combinations. Comparison of results with data from a previously published survey showed little change in susceptibility except for increased resistance of Bacteroides fragilis to ceftriaxone and Clostridium species (not C perfringens) to clindamycin. CONCLUSION: Our results update the local susceptibility profile of anaerobic bacteria and may be considered when choosing an antimicrobial agent for prophylaxis or treatment of anaerobic infections.

Detection of decreased penicillin susceptibility in viridans group streptococci.

One hundred consecutive clinically significant viridans group streptococcal isolates had their susceptibility to penicillin determined by the penicillin E-test method. The ability of penicillin 2 and 10 unit disks and the oxacillin 1 microg disk to detect reduced penicillin susceptibility, ie; MIC > or = 0.25 microg/ml, in viridans group streptococci was determined by comparing the zone diameters against the penicillin E-test MICs. The sensitivity, specificity and predictive values of previous, existing and proposed interpretative criteria to detect decreased penicillin susceptibility were determined. Thirty-seven per cent of the isolates had reduced susceptibility to penicillin. The previous 1993 NCCLS interpretative criteria for the penicillin 10 unit disk, ie; resistant < or = 27 mm failed to detect 16 of 37 (43%) isolates with reduced penicillin susceptibility. The 1 microg oxacillin disk using existing meningococcal interpretative criteria, ie; resistant < or = 10 mm, failed to detect 11 of 37 (40%) isolates with reduced penicillin susceptibility. When the oxacillin 1 microg disk pneumococcal interpretative criteria were used, ie; resistant < or = 19 mm, all the isolates with reduced penicillin susceptibility were detected but 42 of 63 (67%) susceptible isolates were misclassified as resistant. Based on our data, we set new interpretative criteria to detect all isolates with decreased penicillin susceptibility for each of the three disks. Using our proposed zone diameters to detect decreased penicillin susceptibility of < or = 27 mm for the penicillin 2 unit disk, < or = 35 mm for the penicillin 10 unit disk, and < or = 17 mm for the oxacillin disk, 34 (54%), 44 (70%),and 21 (33%) of the 63 susceptible isolates, respectively, were misclassified as having decreased penicillin susceptibility. Our data show that the oxacillin 1 microg disk is able to detect decreased susceptibility to penicillin in viridans group streptococci with greater specificity than either penicillin 2 or 10 unit disks.

Surveillance for antimicrobial resistance in enterococci.

AIM: To describe antimicrobial resistance patterns of Enterococcus species in Auckland. BACKGROUND: Antimicrobial resistant enterococci have emerged as major nosocomial pathogens in overseas hospitals. It is recommended that hospitals perform periodic surveys to determine local enterococcal resistance patterns. METHODS: Enterococcal isolates from four patient groups were tested: group I were recovered from routine clinical specimens; group II were stool isolates from patients at risk of having vancomycin resistant enterococci, eg, intensive care unit patients, patients receiving vancomycin, and immunocompromised patients receiving antibiotics; group III were enterococci from stool specimens sent for Clostridium difficile toxin testing; group IV were isolates from stool specimens submitted to a community laboratory for enteric pathogen testing. All enterococci isolated were tested for the presence of beta-lactamase, susceptibility to amoxycillin, teicoplanin, vancomycin, and for high level gentamicin and streptomycin resistance. RESULTS: There were 121 group I enterococcal isolates. 628 stool specimens were cultured. Enterococci were isolated from: 76/148 (51%) group II specimens; 166/279 (60%) group III specimens; and 70/201 (35%) of group IV specimens. Antimicrobial susceptibility testing was performed on 433 isolates; 74% were E faecalis, 12% E faecium, 6% E gallinarum/casseliflavus group and 8% other enterococcal species. No isolate produced beta-lactamase. All E faecalis were susceptible to amoxycillin. Two E faecium and one enterococcus species were resistant to amoxycillin (MICs all 16 mg/L). All isolates were susceptible to teicoplanin. Fourteen E gallinarum/casseliflavus group isolates had intermediate susceptibility to vancomycin (MICs of 8 mg/L). One E faecium had intermediate susceptibility to vancomycin (MIC 8 mg/L). High level gentamicin and streptomycin resistance occurred in 64 (15%) and 50 (12%) isolates respectively. CONCLUSION: Vancomycin resistance is rare and is essentially restricted to species that are rarely clinical pathogens, i.e., E casseliflavus and E gallinarum. Our results have established the local susceptibility profile for enterococcal isolates. This allows comparison with other locations and the detection of emerging trends of resistance.

Assessment of the yield of anaerobic blood cultures.

Because of the declining incidence of anaerobic bacteremia, the predictable sites of anaerobic infection and the increasing importance of aerobic isolates (eg; yeasts), the practice of routinely culturing half the volume of blood collected anaerobically has been questioned. We have assessed the yield of routine anaerobic blood cultures in our clinical setting. Blood culture isolates from November 1994 through October 1995 at Auckland (AKH) and Green Lane/National Women's Hospitals (GL/NWH) were recorded. The medical records of patients with anaerobic bacteremia were examined. For the three month period April to June 1996, all positive blood cultures were analysed with respect to which bottle (aerobic or anaerobic or both) was positive. For the period November 1994 to October 1995, 5.6% and 5.3% of blood cultures at AKH and GLH respectively were positive. At AKH and GLH anaerobes constituted 0.16% and 0.19% of all blood cultures and 3.1% and 3.5% of all positive blood cultures respectively. Twenty-one of 25 (84%) significant anaerobes were from patients in whom anaerobic infection was predictable. More isolates were recovered from aerobic than anaerobic bottles, 178 versus 71, p < 0.001. Aerobic culture also recovered more pathogens (76 versus 38, p < 0.001 more yeasts (10 versus 0) and more Pseudomonas spp. (10 versus 1) than did anaerobic culture. Only obligate anaerobes were isolated more frequently in anaerobic bottles (5 versus 0, p = 0.03). Most instances of anaerobic bacteremia occurred in patients where anaerobes could be expected. We conclude that routine use of two aerobic bottles with clinically directed use of anaerobic blood culture bottle is an appropriate and effective approach in our setting.