Diversity of community acquired MRSA carrying the PVL gene in Queensland and New South Wales, Australia

Emergence and dissemination of community acquired methicillin resistant Staphylococcus aureus (CA-MRSA) strains are being reported with increasing frequency in Australia and worldwide. These strains of CA-MRSA are genetically diverse and distinct in Australia. Genotyping of CA-MRSA using eight highly-discriminatory single nucleotide polymorphisms (SNPs) is a rapid and robust method for monitoring the dissemination of these strains in the community. In this study, a SNP genotyping method was used to investigate the molecular epidemiology of 249 community acquired non-multiresistant MRSA (nm-MRSA) isolates over a 12-month period from routine diagnostic specimens. A real-time PCR for the presence of Panton-Valentine leukocidin (PVL) was also performed on these isolates. The CA-MRSA isolates were sourced from a large private laboratory in Brisbane, Australia that serves a wide geographic region encompassing Queensland and Northern New South Wales. This study identified 16 different STs and 98% of the CA-MRSA isolates were positive for the PVL gene. The most common ST was ST93 with 41% of isolates testing positive for this clone.

Community onset staphylococcus aureus infections in Melbourne

Objective: To investigate the relative importance of methicillin resistant Staphylococcus aureus (MRSA) in the community in Melbourne by describing circulating S. aureus strains and infection characteristics.

Methods: Patients with any community-onset S. aureus infection were identified via clinical specimens submitted to a community-based pathology service in 2006. The referring doctors confirmed community onset and defined site and severity of each infection. Patient isolates were characterised by antibiotic resistance subtype and presence of the Panton-Valentine leukocidin gene (pvl).

Results: Between April and September 2006, 2,094 S. aureus isolates were processed. Of these, 133 (6.4%) were multiresistant MRSA (mMRSA) and 110 (5.3%) were resistant to less than 3 non-betalactam antibiotics (non-multiresistant MRSA or nmMRSA). We followed-up all nmMRSA (34) and mMRSA (15) confirmed community-onset infections, and a random subset of eligible patients with MSSA infections (57), for whom clinical data were available from referring doctors (82% response).

The majority of isolates were from skin infections (99/106), but drainage was performed in less than one third of cases (29/99). Antibiotics were prescribed for 89% (95%CI: 82, 94) of infections. The isolates were resistant to the prescribed antibiotic 100% of the time for mMRSA infections and 80% for nmMRSA. Those with infections caused by MRSA had on average one additional visit to their doctor compared with MSSA infections.

Ten nmMRSA clones were identified, including one new pvl positive nmMRSA. Of the 29 nmMRSA isolates, 14 were pvl positive (48%; 95%CIs: 30%, 66%) compared with 16% of MSSA and 0% mMRSA.

Patients with an infection caused by pvl positive strains (23) were younger ((mean age 23 years (95%CI: 16, 30) compared with the 55 years (95%CI: 50, 61)). Infection site also varied with presence of pvl; more pvl positive infections were found in the axilla (17.9% compared with 0%) and head and neck (35.7% compared with 8.2%), and less for the leg or foot (21.4% compared with 55.7%).

Conclusions: We estimate that 3.5% of community-onset S. aureus infections in Melbourne in 2006 were caused by MRSA, and 70 to 90% of patients with MRSA infections were treated initially with antibiotics to which their isolate was resistant. pvl positive isolates of S. aureus were associated with younger age and axillary or head and neck infections.

Community-onset Staphylococcus aureus infections presenting to general practices in South-eastern Australia

Community-acquired Staphylococcus aureus infections are a public health concern, yet little is known about infections that do not present to hospital. We identified community-onset S. aureus infections via specimens submitted to a community-based pathology service. Referring doctors confirmed eligibility and described infection site, severity and treatment. Isolates were characterized on antibiotic resistance, PFGE, MLST/SCCmec, and Panton–Valentine leukocidin (PVL), representing 106 community-onset infections; 34 non-multiresistant methicillin-resistant S. aureus (nmMRSA) (resistant to <3 non-β-lactam antibiotics), 15 multiply antibiotic-resistant MRSA (mMRSA) and 57 methicillin-sensitive S. aureus (MSSA). Most (93%) were skin and soft tissue infections. PVL genes were carried by 42% of nmMRSA isolates [95% confidence interval (CI) 26–61] and 15% of MSSA (95% CI 8–28). PVL was associated with infections of the trunk, head or neck (56·4% vs. 24·3%, P= 0·005) in younger patients (23 vs. 52 years, P< 0·001), and with boils or abscesses (OR 8·67, 95% CI 2·9–26·2), suggesting underlying differences in exposure and/or pathogenesis.

Antimicrobial resistance in Staphylococcus aureus in Australian teaching hospitals, 1989-1999

An annual survey of antimicrobial resistance in clinical isolates of Staphylococcus aureus was conducted in 21 Australian teaching hospital microbiology laboratories in eight major cities from 1989 to 1999. A total of 19,000 isolates were tested for susceptibility to 18 antimicrobials, with 3795 being methicillin-resistant (MRSA). Resistance to ciprofloxacin in MRSA increased from 4.9% to 75.9%. The proportion of MRSA resistant to erythromycin decreased significantly (99.0%-88.9%), as did that to trimethoprim (98.4%-82.4%) and to tetracycline (96.5%-80.1%). The proportion of MRSA isolated increased in Sydney, Melbourne, Canberra, Adelaide, Perth, and Darwin, but not in Brisbane. The proportion in Hobart peaked in 1994. MRSA in Perth were predominantly non-multiresistant (nmMRSA) throughout the survey (i.e., resistant to less than three of eight indicator antibiotics) due mainly to local strains that originated in the community. The proportion of nmMRSA increased to modest levels in the other cities. In eastern cities, this was due to the appearance of strains closely related to nmMRSA seen in other countries of the southwestern Pacific.

Emergence of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infection in Queensland, Australia

Objectives: To investigate the incidence and epidemiology of non-multiresistant methicillin-resistant Staphylococcus aureus (nmMRSA) infection in south-east Queensland, Australia. Study design: A retrospective survey was done of hospital records of all patients who had non-multiresistant MRSA isolated at Ipswich Hospital (a 250-bed general hospital, 40 km south-west of Brisbane, Queensland, Australia) between March 2000 and June 2001. Laboratory typing of these isolates was done with antibiogram, pulsed-field gel electrophoresis, bacteriophage typing and coagulase gene typing. Results: There were 44 infections caused by nmMRSA. Seventeen infections (39%) occurred in patients from the south-west Pacific Islands (predominantly Samoa, Tonga and New Zealand). Laboratory typing showed that the isolates in Pacific Islanders were Pacific Island strains, and 16/17 of these infections were community acquired. Twenty-three infections (52%) occurred in Caucasians. Eleven of the isolates from Caucasians (48%) were a new predominantly community-acquired strain that we have termed the ‘R’ pulsotype, nine (39%) were Pacific Island strains, and three (13%) were health care institution-associated strains. Four infections occurred in patients who were not Caucasians or Pacific Islanders. Overall, 34 of all 44 infections (77%) were community' acquired. Conclusions: Non-multiresistant MRSA infection, relatively frequently observed in Pacific Islanders in south-east Queensland, is now a risk for Caucasians as well, and is usually community acquired. Clinicians should consider taking microbiological specimens for culture and antimicrobial susceptibility testing in patients with suspected staphylococcal infections who are not responding to empirical therapy with β-lactam antibiotics.

Methicillin-resistant Staphylococcus aureus in the Australian community: an evolving epidemic

Objective: To describe antimicrobial resistance and molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) isolated in community settings in Australia. Design and setting: Survey of S. aureus isolates collected prospectively Australia-wide between July 2004 and February 2005; results were compared with those of similar surveys conducted in 2000 and 2002. Main outcome measures: Up to 100 consecutive, unique clinical isolates of S. aureus from outpatient settings were collected at each of 22 teaching hospital and five private laboratories from cities in all Australian states and territories. They were characterised by antimicrobial susceptibilities (by agar dilution methods), coagulase gene typing, pulsed-field gel electrophoresis, multilocus sequence typing, SCCmec typing and polymerase chain reaction tests for Panton-Valentine leukocidin (PVL) gene. Results: 2652 S. aureus isolates were collected, of which 395 (14.9%) were MRSA. The number of community-associated MRSA (CA-MRSA) isolates rose from 4.7% (118/2498) of S. aureus isolates in 2000 to 7.3% (194/2652) in 2004 (P=0.001). Of the three major CA-MRSA strains, WA-1 constituted 45/257 (18%) of MRSA in 2000 and 64/395 (16%) in 2004 (P=0.89), while the Queensland (OLD) strain increased from 13/257 (5%) to 58/395 (15%) (P=0.0004), and the south-west Pacific (SWP) strain decreased from 33/257 (13%) to 26/395 (7%) (P=0.01). PVL genes were detected in 90/195 (46%) of CA-MRSA strains, including 5/64 (8%) of WA-1, 56/58 (97%) of OLD, and 25/26 (96%) of SWP strains. Among health care-associated MRSA strains, all AUS-2 and AUS-3 isolates were multidrug-resistant, and UK EMRSA-15 isolates were resistant to ciprofloxacin and erythromycin (50%) or to ciprofloxacin alone (44%). Almost all (98%) of CA-MRSA strains were non-multiresistant. Conclusions: Community-onset MRSA continues to spread throughout Australia. The hypervirulence determinant PVL is often found in two of the most common CA-MRSA strains. The rapid changes in prevalence emphasise the importance of ongoing surveillance.

Correcting for bias when estimating the cost of hospital-acquired infection : an analysis of lower respiratory tract infections in non-surgical patients

Hospital acquired infections (HAI) are costly but many are avoidable. Evaluating prevention programmes requires data on their costs and benefits. Estimating the actual costs of HAI (a measure of the cost savings due to prevention) is difficult as HAI changes cost by extending patient length of stay, yet, length of stay is a major risk factor for HAI. This endogeneity bias can confound attempts to measure accurately the cost of HAI. We propose a two-stage instrumental variables estimation strategy that explicitly controls for the endogeneity between risk of HAI and length of stay. We find that a 10% reduction in ex ante risk of HAI results in an expected savings of £693 ($US 984).

A Petrov-Galerkin method for a singularly perturbed ordinary differential equation with non-smooth data

In this paper, a singularly perturbed ordinary differential equation with non-smooth data is considered. The numerical method is generated by means of a Petrov-Galerkin finite element method with the piecewise-exponential test function and the piecewise-linear trial function. At the discontinuous point of the coefficient, a special technique is used. The method is shown to be first-order accurate and singular perturbation parameter uniform convergence. Finally, numerical results are presented, which are in agreement with theoretical results.