Population dynamics of methicillin-susceptible and -resistant Staphylococcus aureus in remote communities.

OBJECTIVES: Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) was first reported in remote regions of Western Australia (WA) in 1992 and is now the predominant MRSA isolated in the State. To gain insights into the emergence of CA-MRSA, 2146 people living in 11 remote WA communities were screened for colonization with S. aureus. METHODS: Antibiogram analysis, contour-clamped homogeneous electric field electrophoresis, multilocus sequence typing, Panton-Valentine leucocidin determinant detection and accessory genetic regulator typing were performed to characterize the isolates. MRSA was further characterized by staphylococcal cassette chromosome mec typing. RESULTS: The S. aureus population consisted of 13 clonal complexes and two Singleton lineages together with 56 sporadic isolates. Five lineages contained MRSA; however, these were not the predominant methicillin-susceptible S. aureus (MSSA) lineages. There was greater diversity amongst the MSSA while the MRSA appeared to have emerged clonally following acquisition of the staphylococcal cassette chromosome mec. Three MRSA lineages were considered to have been endemic in the communities and have subsequently become predominant lineages of CA-MRSA in the wider WA community. People colonized with MSSA tended to harbour clones of a different genetic lineage at each anatomical site while people colonized with MRSA tended to harbour clones of the same lineage at each site. Overall, the isolates were resistant to few antimicrobials. CONCLUSIONS: Although the evidence suggests that in WA CA-MRSA strains arose in remote communities and have now disseminated into the wider community, there is no evidence that they arose from the predominant MSSA clones in these communities.

2004 Lowbury Lecture: the Western Australian experience with vancomycin-resistant enterococci - from disaster to ongoing control.

The first hospital outbreak of a vancomycin-resistant enterococcus (VRE) in Western Australia (WA) started in the Royal Perth Hospital in July 2001 and initially involved the Intensive Care Unit (ICU) and the Nephrology and Dialysis Units. The outbreak was caused by vancomycin-resistant Enterococcus faecium (VREF) of the vanB genotype. Pulsed-field gel electrophoresis and plasmid analysis of the isolates demonstrated a single-strain outbreak. Despite the isolation of carriers and implementation of all the additional precautions recommended to control VRE, VREF spread rapidly. Two months after the index patient was detected, the epidemic strain had spread to 22 wards and units and one outpatient unit (Satellite Dialysis). Four patients were infected and 64 were colonized. A Hospital VRE Executive Group, which included the Chief Executive and Directors of Clinical Services and Nursing, was formed to eradicate the outbreak and to prevent the epidemic strain from becoming endemic in the hospital. The WA Department of Health agreed to provide substantial extra funding to enable the hospital to use expensive enhanced infection control practices, as follows. Control was handicapped by the slowness of conventional laboratory methods, which took four to five days to identify VRE and allowed environmental contamination and nosocomial transmission to occur before carriers were detected and isolated. A laboratory procedure to make rapid provisional identification of VRE within 30-48h was developed by performing multiplex polymerase chain reaction (PCR) for vanA and vanB genes directly on 24-h selective enrichment broth cultures. On average, four rectal swabs, each collected on separate days, were needed to detect >90% of carriers. In total, 1977 ward contacts were screened after discharge from hospital and 54 (2.73%) were found to be carrying VREF. The electronic labelling and active follow-up of ward contacts resulted in a significant number of carriers being detected who otherwise posed a risk of initiating further outbreaks in hospital if they were re-admitted. The outbreak was terminated after five months and the cost of the enhanced infection control practices was 2,700 000 Australian dollars (1,000,000 pounds sterlings). Ongoing control has been facilitated by targeted active surveillance cultures: on admission to high-risk units (ICU, Burns, Nephrology, Haematology, Bone Marrow Transplant Unit), on transfer out of the ICU to other hospital units, by monthly screening of patients regularly attending Dialysis Units, and by opportunistic laboratory screening of inpatient faecal specimens submitted for Clostridium difficile culture and toxin. Vigilance needs to be maintained as the epidemic strain of VREF remains in the Perth community. Ward contacts of the first outbreak have caused small outbreaks in two hospitals, and seven to 19 sporadic new carriers have been detected annually since the first outbreak. The key elements of the VRE control programme are as follows: To date, this programme has prevented VRE from becoming established in any WA hospital.

Detection of Helicobacter pylori antigen in faeces by enzyme immunoassay.

The detection of Helicobacter pylori antigen directly in faecal specimens may offer an alternative non-invasive method for determining the presence of H. pylori infection. This study compared the performance of the Premier Platinum HpSA enzyme immunoassay (HpSA) with histology and CLOtest, a rapid urease test. Of 134 patients undergoing upper gastrointestinal endoscopy, 37 (28%) were H. pylori-positive by histology and CLOtest. Using the HpSA test, H. pylori was detected in 35 H. pylori-positive patients (95% sensitivity) and one H. pylori-negative patient (99% specificity). The positive and negative predictive values for HpSA were 97 and 98%, respectively. HpSA is a rapid, easily performed, non-invasive method for detecting H. pylori.

Case of Staphylococcus schleiferi endocarditis and a simple scheme to identify clumping factor-positive staphylococci.

Staphylococcus schleiferi is a coagulase-negative staphylococcus infrequently reported as a human pathogen. We report a case of prosthetic valve endocarditis attributed to this organism, contrast it to another Staphylococcus species that gives similar clumping factor results (S. lugdunensis), and propose a simple, effective identification scheme for identification of clumping factor-positive staphylococci.

Community strain of methicillin-resistant Staphylococcus aureus involved in a hospital outbreak.

Western Australia (WA) has been able to prevent methicillin-resistant Staphylococcus aureus (MRSA) strains from outside of the state from becoming established in its hospitals. Recently, a single-strain outbreak of MRSA occurred in a WA metropolitan teaching hospital following admission of an infected patient from a remote community. The strain responsible for the outbreak was unrelated to any imported strains and spread rapidly in the hospital. Screening of two remote communities in the region from which the index case came revealed that 42% of the people in one community and 24% in the other carried MRSA. Isolates were typed by resistance pattern, plasmid analysis, contour-clamped homogeneous electric field electrophoresis, bacteriophage pattern, and coagulase gene restriction fragment length polymorphism. It was found that of the people carrying MRSA, 39% in the former community and 17% in the latter community were carrying an MRSA strain which was indistinguishable from the strain that caused the hospital outbreak.

Investigation of a cluster of Staphylococcus aureus invasive infection in the top end of the Northern Territory.

INTRODUCTION: Staphylococcus aureus invasive infection remains a serious condition associated with considerable morbidity and mortality. Following notification of five cases at Royal Darwin Hospital (RDH), we searched for related cases, determined their epidemiological characteristics and attempted to identify the source of this apparent cluster. METHODS: We reviewed RDH microbiology records between June 1996 and April 1997 for S. aureus isolates with similar antibiograms to notified cases. We used antibiotic resistance patterns, bacteriophage typing and two molecular typing techniques to subtype implicated isolates. Hospital records were reviewed for admission details and associated costs were estimated. RESULTS: Fifty-four cluster-related isolates occurred in 47 separate presentations. The peak incidence was in the wet season. The most important risk factor for staphylococcal invasive infection was the presence of skin sores/scabies in 17/54 cases (31%), followed by intravascular line use in 14/54 (26%), open trauma in 11/54 (20%), underlying end stage renal failure and alcoholism each in ten of 54 (18%). The mean admission length was 30 days and antibiotics were given for an average of 23 days. Death due to S. aureus infection occurred in eight of 47 (17%) presentations. S. aureus pneumonia was community acquired in 12/13 patients (92%) and six of 13 (46%) died. Ten of 13 (80%) pneumonia patients had at least one other focus of S. aureus infection. The cost of antibiotics and hospital bed per presentation was approximately $16,000. Presentations with skin sores/scabies cost considerably more ($31,000). No common epidemiologic features were found for community or hospital acquired cases. CONCLUSION: Considerable mortality and cost was attributable to cases of S. aureus invasive infection during this cluster; particularly those with community acquired pneumonia or skin sores/scabies. Staphylococcal antibiotic cover should be considered early for unwell patients presenting to hospital with pneumonia and other signs of potential S. aureus infection. It is appropriate to target public health efforts to prevent skin sores and to provide adequate treatment when they occur.

Diagnosis of Chlamydia trachomatis and Neisseria gonorrhoeae. Genitourinary infections in males by the Amplicor PCR assay of urine.

The Amplicor CT/NG polymerase chain reaction (PCR) test on urine specimens from males was prospectively evaluated against established specimens and laboratory methods for diagnosing Chlamydia trachomatis and Neisseria gonorrhoeae genitourinary infections, in patients from a remote region of Western Australia. Seventy-three males who were tested for both C. trachomatis and N. gonorrhoeae by both conventional methodology and Amplicor PCR on urine were enrolled in the study. Established testing comprised enzyme immunoassay/immunofluorescence antigen testing (EIA/IF) for C. trachomatis and microscopy and/or culture for N. gonorrhoeae on urethral swabs. Positive test results were confirmed using a set of criteria that included supplemental PCR testing and clinical history. Overall, 13.7% of patients were resolved as positive for C. trachomatis and 52.1% as positive for N. gonorrhoeae. The sensitivity and specificity of the Amplicor CT/NG PCR on male urine specimens for C. trachomatis were 80.0% (8/10) and 95.2% (60/63), compared with 60.0% (6/10) and 100.0% (63/63) for EIA/IF on urethral swabs. For N. gonorrhoeae, the sensitivity and specificity of the Amplicor CT/NG PCR on male urine specimens were both 100% (38/38 and 35/35, respectively) compared with 86.8% (33/38) and 100% (35/35) for microscopy and/or culture on urethral swabs. The results of this study indicate that the Amplicor CT/NG multiplex PCR test for C. trachomatis and N. gonorrhoeae performed on urine in males provides a highly sensitive, specific, and robust method for the diagnosis of both C. trachomatis and N. gonorrhoeae, for the early detection of both symptomatic and asymptomatic infected individuals.

A rapid (20 h) solid screening medium for detecting methicillin-resistant Staphylococcus aureus.

Methicillin aztreonam mannitol salt agar is a sensitive and reliable solid screening medium for detecting methicillin-resistant Staphylococcus aureus (MRSA). With this medium an incubation period of only 20 h is sufficient to either produce visible colonies of MRSA or to exclude MRSA (no staphylococcal colonies). Coagulase testing (requiring a further 6 h) enables coagulase-positive isolates to be provisionally reported as 'possible MRSA' 26-30 h after the swabs were collected. The medium supports growth of intrinsically resistant staphylococci including low-expression-class MRSA (methicillin minimum inhibitory concentration (MIC) 8-16 mg/L), but methicillin susceptible staphylococci and beta-lactamase hyperproducers are suppressed.

Colony variation in Staphylococcus lugdunensis.

Staphylococcus lugdunensis is being increasingly reported as a pathogen with an outcome resembling that of S. aureus rather than coagulase-negative staphylococci. Recent local isolates exhibited colonial variation that delayed identification and interpretation of clinical significance. Until now previous descriptions have not emphasized colonial variation as an important identifying characteristic of S. lugdunensis.

Evaluation of a commercial polymerase chain reaction assay for the detection of Chlamydia trachomatis.

Cell culture has traditionally been considered the most sensitive method for detecting Chlamydia trachomatis from clinical specimens, but depends upon the organisms being viable at the time of cell inoculation. Furthermore, cell culture is slow and labor intensive. Even when a special transport medium is used, there is a progressive loss of viability of C. trachomatis during transport. The detection of C. trachomatis by cell culture is more rapid when immunofluorescence is used to detect early antigen, but requires considerable experience to interpret. The Amplicor C. trachomatis system is a commercial polymerase chain reaction (PCR)-based assay combined with nucleic acid hybridization for the direct detection of C. trachomatis in urine and swabs of appropriate sites, with results available within 6 h. All specimens for C. trachomatis received by the Royal Perth Hospital Department of Microbiology during the period 1 July 1994 to 30 June 1995 that were suitable for culture and Amplicor PCR were tested by both methods (2029 specimens). Discordant results were obtained in nine cases and resolved by additional testing. Seventy-one specimens were confirmed as true positives, of these Amplicor PCR correctly detected 67 (sensitivity 94.4%) and culture correctly detected 62 (sensitivity 87.3%). The Amplicor PCR assay was found to be more sensitive and as specific as culture. It had the added advantages of ease of use, rapid availability of results, standardization and was more suited than culture to processing large number of specimens.

Detection of antibodies to Bartonella henselae in clinically diagnosed cat scratch disease.

OBJECTIVE: To determine the usefulness of an indirect immunoflourescence antibody test for antibodies to Bartonella henselae in diagnosing cat scratch disease (CSD). DESIGN AND SETTING: Retrospective case survey of 354 patients whose sera were tested for antibodies to B. henselae at Royal Perth Hospital, Perth, and the Institute of Clinical Pathology and Medical Research, Sydney. In 1994; and measurement of the background prevalence of antibodies to B. henselae. MAIN OUTCOME MEASURES: Prevalence of antibodies to B. henselae, odds of a positive titre (> or = 64) in patients with and without specific risk factors for CSD and clinical features of the disease; prevalence of antibodies to B. henselae in randomly selected blood donors. RESULTS: Demographic, clinical and cat contact data were available for 303 patients. Sixty-four (21.1%) had a positive titre, as did 53 of 98 (54%) patients with a history of cat contact and lymphadenopathy. This proportion increased to 62% (38 of 61 patients) in patients with a history of cat scratch or bite and to 90.3% (28 of 31) in those with cat contact, lymphadenopathy and histological evidence of granulomatous lymphadenitis. Patients who developed lymphadenopathy after cat contact were significantly more likely to have a positive titre than those without this history (odds ratio [OR], 20.8; 95% confidence interval [95% Cl], 9.6-46; P < 0.0001). Inclusion of a history of a cat scratch or bite significantly raised the odds of being seropositive (OR, 13.7; 95% Cl, 6.8-28.1; P < 0.0001), and the presence of granulomas on lymph node biopsy further increased the odds (OR, 124.4; 95% Cl, 19.4-1073; P < 0.0001). The prevalence of antibodies to B. henselae in random blood donors in New South Wales was about 5% (five of 102 sera samples). CONCLUSIONS: The immunofluorescence antibody test for B. henselae can be expected to be positive in just over half the patients with clinically suspected CSD, and it has a positive predictive value of 83%. In a significant number of cases the diagnosis cannot be made on the basis of the results of immunofluorescence antibody testing alone and further investigations, including lymph node biopsy, may be required.

Bartonella henselae is a causative agent of cat scratch disease in Australia.

We report the first isolation of Bartonella henselae from the blood and fleas of a cat of a patient with cat scratch disease (CSD) in Australia. A 49-year-old man presented with a history that 3 weeks after he had removed fleas from his cat he had developed fever, lethargy and anorexia for 3 days. This was followed by the appearance of axillary lymphadenopathy. There was no history of a bite or scratch and no primary lesion on the skin. Two fine needle aspirates of the axillary lymph node showed granulomatous lymphadenitis with no organisms seen by Warthin-Starry silver staining or electron microscopy. No organism was cultured from the patient's lymph node aspirates or blood cultures processed by lysis centrifugation. However, the polymerase chain reaction (PCR) using p24E and p12B primers gave a 280 bp band indistinguishable from Bartonella henselae when using DNA extracted from the lymph node aspirates and the patient's blood leucocytes. DNA sequencing of the PCR product from the patient's blood showed that the DNA was from Bartonella henselae. The patient's serum had a titre of 1024 in an indirect immunofluorescence antibody test for Bartonella henselae. Bartonella henselae was subsequently cultured from fleas and blood taken from the patient's cat. This case provides evidence that Bartonella henselae is a causative agent of CSD in Australia and supports a possible role for fleas in transmission of the disease.

Changing epidemiology of methicillin-resistant Staphylococcus aureus in Western Australia.

OBJECTIVE: To assess the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in Western Australia. DESIGN: Retrospective review of statutory notification data. SETTING: Western Australia (WA), 1993. OUTCOME MEASURES: Notification rates, antibiotic resistance patterns and classification of isolates as imported or WA MRSA strains on the basis of antibiotic susceptibility. RESULTS: There were 204 notifications of MRSA, 78% of which were classified as WA MRSA. Three outbreaks of MRSA infection and colonisation occurred in separate WA hospitals. Notification rates per 100,000 were highest in the rural regions: the Kimberley (86.32), Goldfields (62.47), Mid West (37.21) and Pilbara (27.38) regions; and lowest in the metropolitan regions (5.52). All MRSA isolates were susceptible to vancomycin. Most imported strains were susceptible to amikacin, bacitracin, chloramphenicol, framycetin, fusidic acid and novobiocin, but only 23% to gentamicin. WA MRSA strains remained predominantly susceptible to all antibiotics tested, except beta-lactams, erythromycin and tetracycline, but a few strains resistant to rifampicin (1%) and fusidic acid (3%) appeared in the second half of 1993. CONCLUSIONS: The epidemiology of MRSA in WA is changing rapidly, with increases in both the numbers of notifications and the proportion from country regions. A new strain of MRSA (WA MRSA) that is less resistant to antibiotics than imported MRSA has emerged and is threatening the State's success in preventing establishment of MRSA in its hospitals.

Emergence of high-level mupirocin resistance in methicillin-resistant Staphylococcus aureus in Western Australia.

Six mupirocin-resistant Staphylococcus aureus were isolated from patients living in the northern part of Western Australia (WA). They were all resistant to methicillin, tetracycline, trimethoprim and cadmium and harboured similar 41.4 kb plasmids. Transfer and curing experiments with one of the isolates, WBG7569, demonstrated that the 41.4 kb plasmid encoded resistance to mupirocin, tetracycline, trimethoprim and cadmium. The isolates were compared by pulsed-field gel electrophoresis with methicillin-resistant S. aureus (MRSA) previously isolated from the Kimberley region in the northern-most part of WA (WA MRSA). The mupirocin-resistant isolates were found to be closely related to WA MRSA suggesting that they were WA MRSA which had acquired a new multiple-resistance plasmid encoding high-level mupirocin resistance.

Genetic analysis of community isolates of methicillin-resistant Staphylococcus aureus in Western Australia.

Methicillin-resistant Staphylococcus aureus (MRSA) obtained from patients who had not been hospitalized outside Western Australia (WA) were studied for antimicrobial resistance and plasmid content and by pulsed-field gel electrophoresis. They were found to be of several types, none of which appeared to be related to MRSA which have been previously studied. It appears that new MRSA strains have emerged in communities in the far north of WA and are being isolated at an increasing frequency in Perth hospitals 2000 km south.