The Who, What, When, and Where of Inpatient Direct Oral Penicillin Challenge-Implications for Health Services Implementation.

Inpatient direct oral challenge programs are increasingly deployed as part of antimicrobial stewardship initiatives to reduce the burden and impacts of penicillin allergy labels on antibiotic prescribing. Using data from a prospective, multicenter cohort inpatient penicillin allergy program, we identify the key targets for delabeling to aid health service implementation.

Penicillin Allergy Delabeling Program: an exploratory economic evaluation in the Australian context.

BACKGROUND: Internationally, clinical and economic advantages of low-risk penicillin delabelling have been explored, supporting changes to healthcare delivery systems where penicillin delabelling is embedded into inpatient usual care. AIMS: To determine if economic advantages of low-risk inpatient penicillin delabelling, described in the international literature, are realised in the Australian context. METHODS: This explorative economic evaluation had prospective patient data collection between January and August 2019, across two Australian health services. Part 1: determine the cost per effectively delabelled patient for Penicillin Allergy Delabeling Program inpatients (PADP cohort) compared with Outpatient Antibiotic Allergy Testing Service outpatients (OAATS cohort). Part 2: a cost analysis to compare hospital costs for inpatients with low-risk penicillin allergy who did (PADP cohort) and did not (usual care cohort) undergo PADP delabelling. RESULTS: Part 1: the PADP (n = 350) and OAATS (n = 27 patients, n = 36 individual visits) cohorts were comparable. In PADP, costs/proportion delabelled was $20.10/0.98, equating to $20.51 per effectively delabelled patient; in OAATS, it was $181.24/0.50, equating to $362. Compared with OAATS, PADP was associated with savings of $341.97 per effectively delabelled patient, indicating the outpatient testing was the dominated strategy, being more costly and less effective. Part 2: the PADP (n = 218) and usual care (n = 32) cohorts were comparable. Significantly favouring the delabelled PADP cohort, the mean difference per patient was -4.41 days (95% confidence interval: -7.64, -1.18) and -$9467.72 (95% confidence interval: -$15 419.98, -$3515.46). CONCLUSIONS: Consistent with international literature, delabelling low-risk penicillin allergies in the inpatient setting had economic advantages in the Australian context. Fully powered economic evaluations are urgently required to consolidate these findings.

The Penicillin Allergy Delabeling Program: A Multicenter Whole-of-Hospital Health Services Intervention and Comparative Effectiveness Study.

BACKGROUND: Penicillin allergies are associated with inferior patient and antimicrobial stewardship outcomes. We implemented a whole-of-hospital program to assess the efficacy of inpatient delabeling for low-risk penicillin allergies in hospitalized inpatients. METHODS: Patients ≥ 18 years of age with a low-risk penicillin allergy were offered a single-dose oral penicillin challenge or direct label removal based on history (direct delabeling). The primary endpoint was the proportion of patients delabeled. Key secondary endpoints were antibiotic utilization pre- (index admission) and post-delabeling (index admission and 90 days). RESULTS: Between 21 January 2019 and 31 August 2019, we assessed 1791 patients reporting 2315 antibiotic allergies, 1225 with a penicillin allergy. Three hundred fifty-five patients were delabeled: 161 by direct delabeling and 194 via oral penicillin challenge. Ninety-seven percent (194/200) of patients were negative upon oral penicillin challenge. In the delabeled patients, we observed an increase in narrow-spectrum penicillin usage (adjusted odds ratio [OR], 10.51 [95% confidence interval {CI}, 5.39-20.48]), improved appropriate antibiotic prescribing (adjusted OR, 2.13 [95% CI, 1.45-3.13]), and a reduction in restricted antibiotic usage (adjusted OR, 0.38 [95% CI, .27-.54]). In the propensity score analysis, there was an increase in narrow-spectrum penicillins (OR, 10.89 [95% CI, 5.09-23.31]) and ß-lactam/ß-lactamase inhibitors (OR, 6.68 [95% CI, 3.94-11.35]) and a reduction in restricted antibiotic use (OR, 0.52 [95% CI, .36-.74]) and inappropriate prescriptions (relative risk ratio, 0.43 [95% CI, .26-.72]) in the delabeled group compared with the group who retained their allergy label. CONCLUSIONS: This health services program using a combination of direct delabeling and oral penicillin challenge resulted in significant impacts on the use of preferred antibiotics and appropriate prescribing.

Matched Case-Control Study of the Long-Term Impact of Beta-Lactam Antibiotic Allergy Testing.

Whereas the short-term impacts of antibiotic allergy testing on delabeling and antibiotic usage have been demonstrated, the long-term impacts have been less well defined. In a single-center matched case-control study from Melbourne, Australia, we demonstrate that a beta-lactam antibiotic allergy testing program has a significant impact on antibiotic usage and infection-related outcomes. This study supports implementation of an antibiotic allergy testing program as a standard of care of antimicrobial stewardship programs.

A Supervised Statistical Learning Approach for Accurate Legionella pneumophila Source Attribution during Outbreaks.

Public health agencies are increasingly relying on genomics during Legionnaires' disease investigations. However, the causative bacterium (Legionella pneumophila) has an unusual population structure, with extreme temporal and spatial genome sequence conservation. Furthermore, Legionnaires' disease outbreaks can be caused by multiple L. pneumophila genotypes in a single source. These factors can confound cluster identification using standard phylogenomic methods. Here, we show that a statistical learning approach based on L. pneumophila core genome single nucleotide polymorphism (SNP) comparisons eliminates ambiguity for defining outbreak clusters and accurately predicts exposure sources for clinical cases. We illustrate the performance of our method by genome comparisons of 234 L. pneumophila isolates obtained from patients and cooling towers in Melbourne, Australia, between 1994 and 2014. This collection included one of the largest reported Legionnaires' disease outbreaks, which involved 125 cases at an aquarium. Using only sequence data from L. pneumophila cooling tower isolates and including all core genome variation, we built a multivariate model using discriminant analysis of principal components (DAPC) to find cooling tower-specific genomic signatures and then used it to predict the origin of clinical isolates. Model assignments were 93% congruent with epidemiological data, including the aquarium Legionnaires' disease outbreak and three other unrelated outbreak investigations. We applied the same approach to a recently described investigation of Legionnaires' disease within a UK hospital and observed a model predictive ability of 86%. We have developed a promising means to breach L. pneumophila genetic diversity extremes and provide objective source attribution data for outbreak investigations.IMPORTANCE Microbial outbreak investigations are moving to a paradigm where whole-genome sequencing and phylogenetic trees are used to support epidemiological investigations. It is critical that outbreak source predictions are accurate, particularly for pathogens, like Legionella pneumophila, which can spread widely and rapidly via cooling system aerosols, causing Legionnaires' disease. Here, by studying hundreds of Legionella pneumophila genomes collected over 21 years around a major Australian city, we uncovered limitations with the phylogenetic approach that could lead to a misidentification of outbreak sources. We implement instead a statistical learning technique that eliminates the ambiguity of inferring disease transmission from phylogenies. Our approach takes geolocation information and core genome variation from environmental L. pneumophila isolates to build statistical models that predict with high confidence the environmental source of clinical L. pneumophila during disease outbreaks. We show the versatility of the technique by applying it to unrelated Legionnaires' disease outbreaks in Australia and the UK.

Hyperexpression of α-hemolysin explains enhanced virulence of sequence type 93 community-associated methicillin-resistant Staphylococcus aureus.

BACKGROUND: The community-associated methicillin-resistant S. aureus (CA-MRSA) ST93 clone is becoming dominant in Australia and is clinically highly virulent. In addition, sepsis and skin infection models demonstrate that ST93 CA-MRSA is the most virulent global clone of S. aureus tested to date. While the determinants of virulence have been studied in other clones of CA-MRSA, the basis for hypervirulence in ST93 CA-MRSA has not been defined. RESULTS: Here, using a geographically and temporally dispersed collection of ST93 isolates we demonstrate that the ST93 population hyperexpresses key CA-MRSA exotoxins, in particular α-hemolysin, in comparison to other global clones. Gene deletion and complementation studies, and virulence comparisons in a murine skin infection model, showed unequivocally that increased expression of α-hemolysin is the key staphylococcal virulence determinant for this clone. Genome sequencing and comparative genomics of strains with divergent exotoxin profiles demonstrated that, like other S. aureus clones, the quorum sensing agr system is the master regulator of toxin expression and virulence in ST93 CA-MRSA. However, we also identified a previously uncharacterized AraC/XylS family regulator (AryK) that potentiates toxin expression and virulence in S. aureus. CONCLUSIONS: These data demonstrate that hyperexpression of α-hemolysin mediates enhanced virulence in ST93 CA-MRSA, and additional control of exotoxin production, in particular α-hemolysin, mediated by regulatory systems other than agr have the potential to fine-tune virulence in CA-MRSA.

Resistance to first-line antibiotic therapy among patients with uncomplicated acute cystitis in Melbourne, Australia: prevalence, predictors and clinical impact.

Background: Australian guidelines recommend trimethoprim or nitrofurantoin as first-line agents for uncomplicated urinary tract infections (UTIs). Laboratory surveillance indicates high rates of trimethoprim resistance among urinary bacterial isolates, but there are scant local clinical data about risk factors and impact of trimethoprim resistance. Objectives: To determine the prevalence, risk factors, mechanism and impact of resistance to first-line antibiotic therapy for uncomplicated UTIs in the community setting. Methods: A prospective observational study from October 2019 to November 2021 in four general practices in Melbourne, Australia. Female adult patients prescribed an antibiotic for suspected or confirmed uncomplicated acute cystitis were eligible. Primary outcome was urine isolates with resistance to trimethoprim and/or nitrofurantoin. Results: We recruited 87 participants across 102 UTI episodes with median (IQR) age of 63 (47-76) years. Escherichia coli was the most common uropathogen cultured (48/62; 77%); 27% (13/48) were resistant to trimethoprim (mediated by a dfrA gene) and none were resistant to nitrofurantoin. Isolates with resistance to a first-line therapy were more common among patients reporting a history of recurrent UTIs [risk ratio (RR): 2.08 (95% CI: 1.24-3.51)] and antibiotic use in the previous 6 months [RR: 1.89 (95% CI: 1.36-2.62)]. Uropathogen resistance to empirical therapy was not associated with worse clinical outcomes. Conclusions: Resistance to trimethoprim is common in uncomplicated UTIs in Australia but may not impact clinical outcomes. Further research is warranted on the appropriateness of trimethoprim as empirical therapy, particularly for patients with antimicrobial resistance risk factors.

Evolution of multidrug resistance during Staphylococcus aureus infection involves mutation of the essential two component regulator WalKR.

Antimicrobial resistance in Staphylococcus aureus is a major public health threat, compounded by emergence of strains with resistance to vancomycin and daptomycin, both last line antimicrobials. Here we have performed high throughput DNA sequencing and comparative genomics for five clinical pairs of vancomycin-susceptible (VSSA) and vancomycin-intermediate ST239 S. aureus (VISA); each pair isolated before and after vancomycin treatment failure. These comparisons revealed a frequent pattern of mutation among the VISA strains within the essential walKR two-component regulatory locus involved in control of cell wall metabolism. We then conducted bi-directional allelic exchange experiments in our clinical VSSA and VISA strains and showed that single nucleotide substitutions within either walK or walR lead to co-resistance to vancomycin and daptomycin, and caused the typical cell wall thickening observed in resistant clinical isolates. Ion Torrent genome sequencing confirmed no additional regulatory mutations had been introduced into either the walR or walK VISA mutants during the allelic exchange process. However, two potential compensatory mutations were detected within putative transport genes for the walK mutant. The minimal genetic changes in either walK or walR also attenuated virulence, reduced biofilm formation, and led to consistent transcriptional changes that suggest an important role for this regulator in control of central metabolism. This study highlights the dramatic impacts of single mutations that arise during persistent S. aureus infections and demonstrates the role played by walKR to increase drug resistance, control metabolism and alter the virulence potential of this pathogen.

Antimicrobial resistance and its detection in Staphylococcus saprophyticus urinary isolates.

The aim of this study was to describe the antibiotic susceptibility of clinical Staphylococcus saprophyticus isolates collected prospectively from urine specimens over a 2-month period from September to October 2022 at a single centre in Melbourne, Australia. Species identification was performed by MALDI-TOF MS. All isolates underwent phenotypic antibiotic susceptibility testing by disc diffusion using European Committee on Antimicrobial Susceptibility Testing (EUCAST) and Clinical and Laboratory Standards Institute (CLSI) guidelines and VITEK2, and mecA polymerase chain reaction. A total of 302 S. saprophyticus isolates from 298 patients were included in this study. Most specimens (91.1%) were referred by community general practitioners from non-hospitalised patients. Antimicrobial resistance to non-ß-lactam antibiotics was uncommon; trimethoprim susceptibility was 97%; trimethoprim/sulfamethoxazole, 98%; nitrofurantoin, 100%; and ciprofloxacin, 100% (100% ciprofloxacin susceptible, increased exposure by EUCAST breakpoints). Methicillin resistance (by mecA detection) was the most common form of urinary antibiotic resistance at 5.6%. VITEK2 susceptibility testing for methicillin resistance had a poor specificity of 61.8% (95% CI 55.8-67.4%) compared to mecA detection. These findings indicate that empiric antibiotic recommendations of trimethoprim, trimethoprim/sulfamethoxazole, and nitrofurantoin for treatment of urinary S. saprophyticus remain appropriate.

Study protocol for PREPARE: a phase II feasibility/safety randomised controlled trial on PeRiopErative Penicillin AlleRgy TEsting.

INTRODUCTION: Patient-reported antibiotic allergy labels (AALs) are common. These labels have been demonstrated to have a negative impact on use of appropriate antibiotics and patient-related health outcomes. These patients are more likely to receive suboptimal antibiotics, have increased rates of surgical site infections and are more likely to be colonised with multidrug-resistant organisms. Increasing recognition that antibiotic allergy forms a key part of good antimicrobial stewardship has led to calls for greater access to antibiotic allergy assessment.PREPARE is a pilot randomised controlled trial of beta-lactam allergy assessment and point of care delabelling in perioperative patients utilising a validated antibiotic allergy assessment tool that has been repurposed into a smartphone application. The aim of the study is to assess the feasibility and safety of this approach in the perioperative outpatient setting. METHODS AND ANALYSIS: Adult participants requiring elective surgery and are likely to require prophylactic intravenous antibiotics will be recruited. During the intervention phase, participants will be randomised to the intervention or control arm, with control patients receiving usual standard of care. Those randomised to intervention undertake a risk assessment via the smartphone application, with those deemed low risk proceeding to direct oral provocation with either a penicillin or cephalosporin. Study outcomes will be evaluated in the postintervention phase, 30 and 90 days after surgery.Feasibility of intervention delivery and recruitment will be reported as proportions with respective 95% CIs. Participants who experience an antibiotic adverse event will be reported by group with respective 95% CIs and compared using modified Poisson regression model with robust SE estimation. ETHICS AND DISSEMINATION: This protocol has received approval from the Austin Health human research and ethics committee, Heidelberg, Victoria, Australia (HREC/17/Austin/575). Results will be disseminated via publication in peer-reviewed journals as well as presentation at international conferences. TRIAL REGISTRATION NUMBER: ACTRN12620001295932.

Efficacy of a Clinical Decision Rule to Enable Direct Oral Challenge in Patients With Low-Risk Penicillin Allergy: The PALACE Randomized Clinical Trial.

Importance: Fewer than 5% of patients labeled with a penicillin allergy are truly allergic. The standard of care to remove the penicillin allergy label in adults is specialized testing involving prick and intradermal skin testing followed by an oral challenge with penicillin. Skin testing is resource intensive, limits practice to specialist-trained physicians, and restricts the global population who could undergo penicillin allergy delabeling. Objective: To determine whether a direct oral penicillin challenge is noninferior to the standard of care of penicillin skin testing followed by an oral challenge in patients with a low-risk penicillin allergy. Design, Setting, and Participants: This parallel, 2-arm, noninferiority, open-label, multicenter, international randomized clinical trial occurred in 6 specialized centers, 3 in North America (US and Canada) and 3 in Australia, from June 18, 2021, to December 2, 2022. Eligible adults had a PEN-FAST score lower than 3. PEN-FAST is a prospectively derived and internationally validated clinical decision rule that enables point-of-care risk assessment for adults reporting penicillin allergies. Interventions: Patients were randomly assigned to either direct oral challenge with penicillin (intervention arm) or a standard-of-care arm of penicillin skin testing followed by oral challenge with penicillin (control arm). Main Outcome and Measure: The primary outcome was a physician-verified positive immune-mediated oral penicillin challenge within 1 hour postintervention in the intention-to-treat population. Noninferiority was achieved if a 1-sided 95% CI of the risk difference (RD) did not exceed 5 percentage points (pp). Results: A total of 382 adults were randomized, with 377 patients (median [IQR] age, 51 [35-65] years; 247 [65.5%] female) included in the analysis: 187 in the intervention group and 190 in the control group. Most patients had a PEN-FAST score of 0 or 1. The primary outcome occurred in 1 patient (0.5%) in the intervention group and 1 patient (0.5%) in the control group, with an RD of 0.0084 pp (90% CI, -1.22 to 1.24 pp). The 1-sided 95% CI was below the noninferiority margin of 5 pp. In the 5 days following the oral penicillin challenge, 9 immune-mediated adverse events were recorded in the intervention group and 10 in the control group (RD, -0.45 pp; 95% CI, -4.87 to 3.96 pp). No serious adverse events occurred. Conclusions and Relevance: In this randomized clinical trial, direct oral penicillin challenge in patients with a low-risk penicillin allergy was noninferior compared with standard-of-care skin testing followed by oral challenge. In patients with a low-risk history, direct oral penicillin challenge is a safe procedure to facilitate the removal of a penicillin allergy label. Trial Registration: ClinicalTrials.gov Identifier: NCT04454229.