Kevin L Schwartz

• Medical Doctor at Public Health Ontario

Background Reliable information on the burden of antimicrobial resistance (AMR) is necessary to confront the threat of antimicrobial resistance. We sought to examine the association between AMR and mortality across cultured bacterial bloodstream pathogens in the province of Ontario, Canada. Methods We used linked microbiology data from 114 hospita...

Background Unnecessarily prolonged antibiotic durations may contribute to the development of resistance in both humans and animals. Veterinarians need evidence supporting antibiotic treatment durations. This systematic review and meta-analysis aimed to compare the efficacy of shorter durations of antibiotic treatment to longer durations in treating...

Background Antimicrobial stewardship programs (ASP) are a crucial component of an overarching One Health approach to mitigate antimicrobial resistance (AMR). Adequate resourcing is a predictor of success for hospital ASPs. To understand the progress of hospital ASPs, we conducted periodic surveys tracking the level of resourcing over time. Methods...

Background Shorter courses of antibiotic therapy are increasingly recommended to reduce antibiotic exposure. However quantifying the real-world impact of duration of therapy is hindered by bias common in observational studies. We aimed to evaluate the harms and benefits of longer versus shorter duration of therapy in older adults. Methods This was...

Background Antimicrobial stewardship programs (ASPs) aim to mitigate antimicrobial resistance (AMR) by optimizing antibiotic use including reducing unnecessary broad-spectrum therapy. This study evaluates the impact of ASP funding and resources on the use of broad-spectrum antibiotics in Ontario hospitals. Methods We conducted a cross-sectional st...

Objective To explore the role of local public health organisations in antimicrobial stewardship (AMS) and antimicrobial resistance (AMR) surveillance. Methods A scoping review was conducted. Peer-reviewed and grey literature from countries within the organisation for economic co-operation and development was searched between 1999 and 2023 using th...

We estimated XBB.1.5 vaccine effectiveness against hospitalization/death among adults aged ≥50 years. Compared with non-XBB.1.5 vaccinees, the initial protection of 64% (95%CI, 57%−69%) was reduced when JN/KP-sublineages became predominant, and quickly declined. No significant protection was observed >6 months post-vaccination. Short durability of...

Background To investigate the prevalence of concomitant bacterial infection across common viral infections. Methods This population-based cohort study included patients infected with influenza A and B (FLUA, FLUB) and respiratory syncytial virus (RSV) in Ontario between 2017 and 2019 and patients with SARS-CoV-2 between 2020 and 2021. Specific bac...

Background Antimicrobial resistant (AMR) pathogens represent an ongoing global health burden. Colonization is often a pre-requisite for infection, but the risk of infection after AMR-colonization is not well understood. Using population-level health administrative data, we sought to investigate the risk of infection with the same AMR organism after...

Background Throughout the COVID-19 pandemic, many jurisdictions established isolation centres to help reduce household transmission; however, few real-world studies support their effectiveness. We compared the risk of transmission among households where first cases used the Toronto Voluntary Isolation Centre (TVIC) compared to households receiving...

Background Group B Streptococcus (GBS) significantly contributes to neonatal sepsis and meningitis, with varying disease rates reported globally and limited population-based data. We estimated infant GBS disease burden in Ontario, Canada and assessed the association of maternal GBS screening (35–37 weeks' gestation) and intrapartum antibiotic proph...

Background Late outbreak identification is a common risk factor mentioned in case reports of large respiratory infection outbreaks in long-term care (LTC) homes. Aim To systematically measure the association between late SARS-CoV-2 outbreak identification and secondary SARS-CoV-2 infection and mortality in residents of LTC homes. Methods We studi...

Background Unnecessary antibiotic prescriptions in primary care are common and contribute to antimicrobial resistance in the population. Audit and feedback (A&F) on antibiotic prescribing to primary care can improve the appropriateness of antibiotic prescribing, but the optimal approach is uncertain. We performed two pragmatic randomized controlled...

Objective To examine the association between maternal mRNA covid-19 vaccination during the first trimester of pregnancy and the prevalence of major congenital anomalies in offspring. Design Population based cohort study with sibling matched analysis. Setting Multiple health administrative databases, linked and analysed at ICES, an independent, no...

Importance There is a recognized unmet need for clinical trials to provide evidence-informed care for infants, children and adolescents. This Special Communication outlines the capacity of 3 distinct trial design strategies, sequential, parallel, and a unified adult-pediatric bayesian adaptive design, to incorporate children into clinical trials an...

Objectives The risk factors and outcomes associated with persistent bacteraemia in Gram-negative bloodstream infection (GN-BSI) are not well described. We conducted a follow-on analysis of a retrospective population-wide cohort to characterize persistent bacteraemia in patients with GN-BSI. Methods We included all hospitalized patients >18 years o...

Objectives To evaluate whether providing family physicians with feedback on their antibiotic prescribing compared with that of their peers reduces antibiotic prescriptions. To also identify effects on antibiotic prescribing from case-mix adjusted feedback reports and messages emphasising antibiotic associated harms. Design Pragmatic, factorial ran...

Background: Coronavirus disease 2019 (COVID-19) vaccination has been associated with reduced outpatient antibiotic prescribing among older adults with laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We assessed the impact of COVID-19 vaccination on outpatient antibiotic prescribing in the broader population of ol...

Objective To compare myocarditis/pericarditis risk after COVID-19 mRNA vaccination versus SARS-CoV-2 infection, and to assess if myocarditis/pericarditis risk varies by vaccine dosing interval. Methods In this retrospective cohort study, we used linked databases in Quebec, Ontario, and British Columbia between January 26, 2020, and September 9, 20...

Background Waning immunity from seasonal influenza vaccination can cause suboptimal protection during peak influenza activity. However, vaccine effectiveness studies assessing waning immunity using vaccinated and unvaccinated individuals are subject to biases. Aim We examined the association between time since vaccination and laboratory-confirmed...

Background Overuse of antimicrobials in residents of long‐term care homes is common and can result in harm. Antimicrobial stewardship interventions are needed in the long‐term care (LTC) homes setting to improve the appropriate use of antimicrobials. Previous literature has highlighted the importance of documenting antimicrobial indication as a str...

Background Cystic echinococcosis (CE) or hydatid disease caused by the cestode Echinococcus granulosus sensu lato is an uncommon infection in Canada especially among children. There are limited reports describing the clinical presentation and management in Canadian children. Methods The medical records of all children diagnosed with CE at a quater...

Background There are limited data on the viral dynamics of SARS-CoV-2 in children. Understanding viral load changes over the course of illness and duration of viral shedding may provide insight into transmission dynamics to inform public health and infection control decisions. Methods We conducted a prospective cohort study of children 18 years an...

Background Randomized trials conducted in low- and middle-income settings demonstrated efficacy of influenza vaccination during pregnancy against influenza infection among infants <6 months of age. However, vaccine effectiveness (VE) estimates from settings with different population characteristics and influenza seasonality remain limited. Methods...

Background Outpatient antibiotic prescribing decreased during the COVID-19 pandemic. Understanding how antibiotic prescribing habits changed differentially based on physician and practice characteristics presents an opportunity to inform antibiotic stewardship. Our objective was to evaluate inter-physician variability and predictors of changes in a...

Introduction We assessed protection from COVID-19 vaccines and/or prior SARS-CoV-2 infection against Omicron-associated severe outcomes during successive sublineage-predominant periods. Methods We used a test-negative design to estimate protection by vaccines and/or prior infection against hospitalization/death among community-dwelling, PCR-tested...

( BMJ . 2023;380:e074035) Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) rates are higher in infants than in older children. Passive immunity has been shown to help prevent other infections, such as pertussis, in infants through the transfer of maternal antibodies following vaccination during pregnancy. SARS-CoV-2 antibodies are found...

The COVID-19 pandemic has likely influenced the epidemiology of bacterial infections through wide-ranging changes to clinical practices and infection control and prevention interventions. We sought to determine how the detection and incidence of bloodstream infections (BSIs) have been influenced by the pandemic. We performed a retrospective analysi...

Background COVID-19 and antimicrobial resistance (AMR) are two intersecting public health crises. Antimicrobial overuse in patients with COVID-19 threatens to worsen AMR. Guidelines are fundamental in encouraging antimicrobial stewardship. We sought to assess the quality of antibiotic prescribing guidelines and recommendations in the context of COV...

Importance The study team previously showed that maternal mRNA COVID-19 vaccination during pregnancy confers protection against SARS-CoV-2 infection and COVID-19–related hospital admission in newborns and young infants. In this study, the study team evaluated newborn and early infant safety outcomes following maternal messenger RNA (mRNA) COVID-19...

Nasopharyngeal swabs (NPS) are considered the standard specimen for SARS-CoV-2 detection by PCR. We aimed to compare detection performance and patient experience of NPS with swish and gargle saliva (SGS) to determine its potential as an accurate, easy-to-collect, and comfortable alternative. We conducted a prospective study from March to May 2021 a...

Objective To evaluate inter-physician variability and predictors of changes in antibiotic prescribing before (2019) and during (2020/2021) the coronavirus disease 2019 (COVID-19) pandemic. Methods We conducted a retrospective cohort analysis of physicians in Ontario, Canada prescribing oral antibiotics in the outpatient setting between January 1,...

We estimated the effectiveness of booster doses of monovalent and bivalent mRNA COVID-19 vaccines against Omicron-associated severe outcomes among adults aged ≥50 years in Ontario, Canada. Monovalent and bivalent mRNA COVID-19 booster doses provided similar, strong initial protection against severe outcomes. Uncertainty remains around waning of pro...

Background Hepatitis C virus (HCV) has high global prevalence and can lead to liver complications and death. Access to direct-acting antivirals (DAAs) in Canada increased following several policy changes, however the real-world impact of expanded DAA access and increased use of these drugs is unknown. Objective We aimed to determine the early chan...

Background Primary care is a critical partner for antimicrobial stewardship efforts given its high human antibiotic usage. Peer comparison audit and feedback (A&F) is often used to reduce inappropriate antibiotic prescribing. The design and implementation of A&F may impact its effectiveness. There are no best practice guidelines for peer comparison...

This cohort study assesses the association between school-based mandatory masking policies and educational disruption in Ottawa, Canada, during the COVID-19 pandemic.

Background Antibiotic overuse and misuse in primary care are common, highlighting the importance of antimicrobial stewardship (AMS) efforts in this setting. Audit and feedback (A&F) interventions can improve professional practice and performance in some settings. Objectives and methods To leverage the expertise from international members of the Jo...

Objective We estimated the effectiveness of booster doses of monovalent and bivalent mRNA COVID-19 vaccines against Omicron-associated severe outcomes among adults aged ≥50 years in Ontario, Canada. Methods We used a test-negative design to estimate vaccine effectiveness (VE), with unvaccinated adults as the comparator, against hospitalization or...

Background: Antibiotics are frequently prescribed unnecessarily in outpatients with COVID-19. We sought to evaluate factors associated with antibiotic prescribing in those with SARS-CoV-2 infection. Methods: We performed a population-wide cohort study of outpatients 66 years or older with PCR-confirmed SARS-CoV-2 from January 1st 2020 to Decembe...

Background: Older adults are recommended to receive influenza vaccination annually and many use statins. Statins have immunomodulatory properties that might modify influenza vaccine effectiveness (VE) and alter influenza infection risk. Methods: Using the test-negative design and linked laboratory and health administrative databases in Ontario,...

Background: Primary care is a critical partner for antimicrobial stewardship efforts given its high human antibiotic usage. Peer comparison audit and feedback (A&F) is often used to reduce inappropriate antibiotic prescribing. The design and implementation of A&F may impact its effectiveness. There are no best practice guidelines for peer compariso...

We estimated the effectiveness of booster doses of monovalent mRNA COVID-19 vaccines against Omicron-associated severe outcomes among adults in Ontario, Canada. We used a test-negative design to estimate vaccine effectiveness (VE) against hospitalization or death among SARS-CoV-2-tested adults aged ≥50 years from January 2 to October 1, 2022, strat...

Objectives: This study aimed to provide real-world evidence on coronavirus disease 2019 vaccine effectiveness (VE) against symptomatic infection and severe outcomes caused by Omicron in children aged 5 to 11 years. Methods: We used the test-negative study design and linked provincial databases to estimate BNT162b2 vaccine effectiveness against s...

Background: Studies conducted during the COVID-19 pandemic have shown that crowding in nursing homes is associated with high incidence of SARS-CoV-2 infections, but this effect has not been shown for other respiratory pathogens. We aimed to measure the association between crowding in nursing homes and outbreak-associated respiratory infection inci...

Background: A randomized controlled trial involving a high-risk, unvaccinated population that was conducted before the Omicron variant emerged found that nirmatrelvir-ritonavir was effective in preventing progression to severe COVID-19. Our objective was to evaluate the effectiveness of nirmatrelvir-ritonavir in preventing severe COVID-19 while Om...

Objective To estimate the effectiveness of maternal mRNA covid-19 vaccination during pregnancy against delta and omicron severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection and hospital admission in infants. Design Test negative design study. Setting Community and hospital testing in Ontario, Canada. Participants Infants young...

Background Global estimates suggest millions of deaths annually are associated with antimicrobial resistance (AMR) but these are generated from scarce data on the relative risk of death attributable to drug-resistant versus drug-sensitive infections. Methods We examined all episodes of E. coli bloodstream infection in Ontario, Canada between 2017...

Background: Solid-organ transplant recipients are at increased risk of developing human papillomavirus-related diseases. Methods: To evaluate the immunogenicity of a quadrivalent vaccine, a prospective observational study included females aged 12-19 years who had received kidney or liver transplants, or were otherwise healthy volunteers. With th...

Background Antimicrobial resistance (AMR) continues to be a global public health issue amid the COVID-19 pandemic; however, unprecedented demands on hospital antimicrobial stewardship programmes (ASPs) potentially altered their core activities. Objective We sought to understand how ASPs have been involved in and impacted by the pandemic. Methods...

Background: Surveillance of antimicrobial resistance is essential to mitigate its impact on population health and inform local empiric treatment practices. Our aims were to evaluate urine culture specimen susceptibility from a range of diverse settings and describe antibiotic susceptibility across all organisms and compare susceptibilities to that...

Background: Our objective was to evaluate the real world effectiveness of nirmatrelvir/ritonavir to prevent severe COVID-19 while Omicron and its subvariants predominate. Methods: We conducted a population based cohort study in Ontario, Canada including all residents >17 years of age who tested positive for SARS-CoV-2 by PCR between 4 April and 31...

Background: To inform planning for further booster doses of COVID-19 vaccines, we estimated the effectiveness of monovalent mRNA vaccines against Omicron-associated severe outcomes in adults over time. Methods: We used a test-negative design and multivariable logistic regression to estimate vaccine effectiveness (VE; 2, 3, or 4 doses compared to un...

Importance Wearing a face mask in school can reduce SARS-CoV-2 transmission but it may also lead to increased hand-to-face contact, which in turn could increase infection risk through self-inoculation. Objective To evaluate the effect of wearing a face mask on hand-to-face contact by children while at school. Design, Setting, and Participants Thi...

Objectives This study evaluated the clinical outcomes associated with use of highly bioavailable oral antibiotics (fluoroquinolones and trimethoprim-sulfamethoxazole) compared to less bioavailable oral antibiotics (beta-lactams) in Gram negative bloodstream infections (BSIs). Methods Among hospitalized older adult patients in Ontario, Canada, disc...

Setting: Rapid antigen screening can be effective in identifying infectious individuals in occupational settings to reduce transmission and outbreaks. We report results from a pilot project at the Greater Toronto Airports Authority (GTAA) and describe the operationalization. Toronto Pearson is a large international airport encompassing over 400 em...

Background Waning protection from two doses of COVID-19 vaccines led to third dose availability in multiple countries even prior to emergence of the Omicron variant. Methods We used the test-negative study design to estimate vaccine effectiveness (VE) against any SARS-CoV-2 infection, symptomatic infection, and severe outcomes (COVID-19-related ho...

Importance: The incidence of SARS-CoV-2 infection, including among individuals who have received 2 doses of COVID-19 vaccine, increased substantially following the emergence of the Omicron variant in Ontario, Canada. Understanding the estimated effectiveness of 2 or 3 doses of COVID-19 vaccine against outcomes associated with Omicron and Delta inf...

Background Unnecessary antibiotic use is associated with adverse side effects and rising rates of resistance at the individual and population level. This study used a theory-informed approach to identify potentially modifiable determinants of antibiotic prescribing for patients presenting to primary care with upper respiratory tract infection sympt...

The COVID-19 pandemic affected access to care, and the associated public health measures influenced the transmission of other infectious diseases. The pandemic has dramatically changed antibiotic prescribing in the community. We aimed to determine the impact of the COVID-19 pandemic and the resulting control measures on oral antibiotic prescribing...

Background: Documenting an indication when prescribing antimicrobials is considered best practice; however, a better understanding of the evidence is needed to support broader implementation of this practice. Objectives: We performed a scoping review to evaluate antimicrobial indication documentation as it pertains to its implementation, prevale...

Background Travellers' perception of their risk for acquiring travel-related conditions is an important contributor to decisions and behaviors during travel. In this study, we aimed to assess the differences between traveller-perceived and expert-assessed risk of travel-related conditions in children and adults travelling internationally and descri...

Background Nonpharmaceutical interventions such as physical distancing and mandatory masking were adopted in many jurisdictions during the COVID-19 pandemic to decrease spread of SARS-CoV-2. We determined the effects of these interventions on incidence of healthcare utilization for other infectious diseases. Methods Using a healthcare administrati...

Background: Geographic trends in antibiotic prescribing show regional variation in antibiotic overuse and antimicrobial resistance, posing a threat to global health care systems. This study's objective was to examine interprovincial variation in outpatient antibiotic dispensing in Canada in 2019. Methods: We conducted a cross-sectional study of...

Bloodstream infections (BSIs) represent a substantial mortality risk, yet most studies are limited to select pathogens or populations. The aim of this study was to describe the population-wide prevalence of BSIs and examine the associated mortality risk for the responsible microorganisms. We conducted a population-wide retrospective cohort study of...

Background: Peer comparison audit and feedback has demonstrated effectiveness in improving antibiotic prescribing practices, but only a minority of prescribers view their reports. We rigorously tested 3 behavioral nudging techniques delivered by email to improve report opening. Methods: We conducted a pragmatic randomized controlled trial among...

We thank Born et al.¹ for their letter in response to our study,² which set out to explore the short-term impacts of the Using Antibiotics Wisely campaign on oral antibiotic use for respiratory tract infections (RTIs). We would like to begin by applauding Choosing Wisely Canada on their leadership and efforts to promote sustainable community antimi...

Background Audit and feedback (A&F) that shows how health professionals compare to those of their peers, can be an effective intervention to reduce unnecessary antibiotic prescribing among family physicians. However, the most impactful design approach to A&F to achieve this aim is uncertain. We will test three design modifications of antibiotic A&F...

Background The incidence of SARS-CoV-2 infection, including among those who have received 2 doses of COVID-19 vaccines, has increased substantially since Omicron was first identified in the province of Ontario, Canada. Methods Applying the test-negative design to linked provincial data, we estimated vaccine effectiveness against infection (irrespec...

Despite decades of stewardship efforts to combat antimicrobial resistance and quantify changes in use, the quality of antibiotic use in British Columbia (BC) remains unknown. As the overuse and misuse of antibiotics drives antibiotic resistance, it is imperative to expand surveillance efforts to examine the quality of antibiotic prescriptions. In l...

Background There is growing evidence supporting the efficacy of shorter courses of antibiotic therapy for common infections, however the risks of prolonged antibiotic duration are underappreciated. Objectives We sought to estimate the incremental daily risk of antibiotic-associated harms. Methods We searched three major databases to retrieve syst...

Background The COVID-19 pandemic has potentially impacted outpatient antibiotic prescribing. Investigating this impact may identify stewardship opportunities in the ongoing COVID-19 period and beyond. Methods We conducted an interrupted time series analysis on outpatient antibiotic prescriptions and antibiotic prescriptions/patient visits in Ontar...

Background: Health care workers have a critical role in the pandemic response to COVID-19 and may be at increased risk of infection. The objective of this study was to assess the seroprevalence of SARS-CoV-2 immunoglobulin G (IgG) antibodies among health care workers during and after the first wave of the pandemic. Methods: We conducted a prospe...

Objectives The COVID-19 pandemic has impacted the incidence of infectious diseases and medical care. This study aimed to describe the impact of the COVID-19 pandemic on community-level antibiotic use. Methods Using national antibiotic dispensing data from IQVIA’s CompuScript database, this ecological study investigated antibiotic dispensing throug...

Objectives Although pertussis vaccines have been widely used for many decades, a burden of illness persists. Resurgences in Ontario, Canada, have not been substantial in the past decade, but an outbreak of pertussis occurred in Toronto between 1 October 2005 and 31 March 2006. Previous Ontario studies found high vaccine effectiveness (VE) in the in...

Objective To estimate the effectiveness of mRNA covid-19 vaccines against symptomatic infection and severe outcomes (hospital admission or death). Design Test negative design study. Setting Ontario, Canada between 14 December 2020 and 19 April 2021. Participants 324 033 community dwelling people aged ≥16 years who had symptoms of covid-19 and we...

Importance As a result of low numbers of pediatric cases early in the COVID-19 pandemic, pediatric household transmission of SARS-CoV-2 remains an understudied topic. Objective To determine whether there are differences in the odds of household transmission by younger children compared with older children. Design, Setting, and Participants This p...

Antimicrobial stewardship interventions in outpatient settings are diverse and a variety of outcomes have been used to evaluate these efforts. This narrative review describes, compares and provides specific examples of antibiotic use and other prescribing measures to help antimicrobial stewards better understand, interpret and implement metrics for...

Importance: Antibiotic overuse contributes to adverse drug effects, increased costs, and antimicrobial resistance. Objective: To evaluate peer-comparison audit and feedback to high-prescribing primary care physicians (PCPs) and assess the effect of targeted messaging on avoiding unnecessary antibiotic prescriptions and avoiding long-duration pre...

Background On 1 November 2018, Choosing Wisely Canada launched their Using Antibiotics Wisely primary care campaign, which aimed to reduce unnecessary antibiotic prescriptions for respiratory tract infections (RTIs) through educational tools for patients and providers. Objectives We explored the impact of this campaign on antibiotic utilization in...