Julianne V. Kus

Purpureocillium lilacinum , a common environmental fungus, can cause hyalohyphomycosis with varied clinical manifestations. Mortality rates can reach 20% with invasive disease. P. lilacinum is intrinsically resistant to amphotericin B, leaving few treatment options. In the absence of clinical breakpoints, epidemiological cutoff values (ECVs) can aid clinicians in monitoring antifungal resistance trends and in guiding initial therapy. We performed antifungal susceptibility testing (AFST) on P. lilacinum isolates to establish minimum inhibitory concentration (MIC) and minimum effective concentration (MEC) distributions and ECVs. Data were collected from 13 laboratories located in seven countries. AFST was performed by broth microdilution (CLSI M38 standard) for itraconazole, voriconazole, posaconazole, isavuconazole, terbinafine, flucytosine, amphotericin B, natamycin, and manogepix. ECVs were established using the iterative statistical method with ECOFFinder (v2.1) following CLSI M57 guidelines. Results from 479 P. lilacinum isolates were analyzed. ECVs were 1 μg/mL for voriconazole, 2 μg/mL for posaconazole, 4 μg/mL for isavuconazole, and 2 μg/mL for terbinafine. Itraconazole displayed a trimodal MIC distribution, although almost all MICs were ≥0.5 µg/mL (mode, 16 μg/mL). Amphotericin B, natamycin, and flucytosine MICs were truncated at the high end of the range and consistent with intrinsic resistance. The manogepix modal MEC was 0.008 μg/mL. These proposed P. lilacinum ECVs and MIC/MEC distributions provide baseline data to monitor resistance trends. Our results confirm that P. lilacinum is intrinsically resistant (IR) to amphotericin B and likely IR to natamycin and flucytosine. Caution is needed in interpreting itraconazole results due to high interlaboratory variability. IMPORTANCE: Purpureocillium lilacinum is a hyaline mold commonly found in the environment and used as an agricultural biopesticide. Infections caused by P. lilacinum can range from fungal eye infections to life-threatening pulmonary and disseminated disease, and mortality rates can be high (up to 20%). Single-center studies examining antifungal susceptibility testing (AFST) data found reduced susceptibility to certain antifungals, but more robust global AFST studies are needed to help interpret MICs and MECs. We performed AFST according to the Clinical Laboratory and Standards Institute reference method in thirteen independent laboratories on 479 P. lilacinum isolates to establish MIC/MEC distributions and epidemiological cutoff values (ECVs) for nine antifungals, including those recommended by global treatment guidelines. The calculated ECVs were 1 μg/mL for voriconazole, 2 μg/mL for posaconazole, 4 μg/mL for isavuconazole, and 2 μg/mL for terbinafine. Our results also confirm that P. lilacinum is intrinsically resistant to amphotericin B and likely intrinsically resistant to natamycin and flucytosine. Caution is needed in interpreting itraconazole AFST results due to high interlaboratory variability. These antifungal in vitro susceptibility data suggest limited options to treat P. lilacinum infections.

Background: Malaria is typically diagnosed using rapid antigen tests and microscopy. This case describes an unusual presentation of Plasmodium falciparum , initially detected via 16S rDNA testing of pericardial fluid identifying apicoplast DNA—a finding not previously reported in the literature. Case Summary: A septuagenarian Nigerian man visiting Canada presented with shortness of breath, tachycardia, tachypnea, anemia, and a pericardial effusion. Pericardiocentesis yielded serosanguineous fluid, and imaging revealed multifocal opacities. Blood and fluid cultures were negative for bacterial organisms. After briefly leaving the hospital against medical advice, he returned in respiratory distress and required intubation for acute respiratory distress syndrome. He received empiric antibiotics for rickettsial infection (due to positive serology) and presumed sepsis. Further workup, including pericardial fluid 16S rDNA PCR and sequencing, identified P. falciparum apicoplast DNA. This was confirmed by malaria antigen and Plasmodium -specific PCR testing of the fluid alongside PCR of whole blood, though microscopy and antigen tests remained negative. Hemozoin-like structures were also identifiable in the pericardial fluid. He was treated with a 3-day course of atovaquone-proguanil for malaria, with subsequent clinical improvement. He remains well on follow-up. Conclusion: This case underscores an uncommon presentation of P. falciparum and, though not a standard or recommended diagnostic tool for malaria, in this case, 16S rDNA analysis aided in the diagnosis. Clinicians should maintain malaria in the differential for patients from endemic regions. Multidisciplinary collaboration was essential in achieving the diagnosis.

Mycoplasma pneumoniae (Mpn) is a common respiratory tract pathogen known to cause cyclic epidemics every 3–4 years. For 4 years (2020–2023), a low positivity rate (0.64%) for Mpn laboratory testing at Public Health Ontario suggested minimal circulation of Mpn in Ontario, Canada, likely owing, in part, to COVID-19-related non-pharmaceutical interventions. In 2024, we observed a dramatic re-emergence of Mpn, characterized by large increases in the number of laboratory-confirmed cases ( n = 1,122) and the positivity rate (19.1%) of laboratory detections. Patient age distribution of Mpn infections in 2024 did not differ from 2018 to 2019; however, analysis of patient setting at the time of specimen collection as a proxy for disease severity saw a significant increase in the proportion of Mpn-positive specimens collected from patients in hospital emergency departments (ED) ( P < 0.001), and a decrease in the proportion from patients in inpatient wards ( P = 0.001). Macrolide-resistant rates were statistically equivalent in 2024 (14.6%) compared to 2018–2019 (12.4%), as was the ratio of p1 -1 and p1 -2 adhesin subtypes. Combined 2018–2024 data show that a significantly greater proportion of Mpn-positive pediatric specimens occurred in community clinics/private practices ( P = 0.001), compared with adults, where a greater proportion were in EDs ( P = 0.012), or intensive/critical care units ( P < 0.001). Our findings suggest that the magnitude of Mpn infections in 2024 was not due to a novel strain, but rather due to the increased transmission of strains previously circulating in Ontario following the cessation of COVID-19 pandemic-related non-pharmaceutical interventions, and exacerbated by population immunity debt and the cyclic nature of Mpn. IMPORTANCE: Mycoplasma pneumoniae (Mpn) is a common cause of community-acquired respiratory infection and is known for causing “atypical” pneumonia. Infections show seasonal and cyclical patterns with larger epidemics every 3–4 years. Because Mpn is transmitted via respiratory droplets, incidence was very low during the COVID-19 pandemic when masking and physical distancing were widely utilized. In late 2023 through 2024, many jurisdictions worldwide reported a surge in Mpn cases. This increase, along with reports of emerging resistance to first-line treatment macrolide antibiotics, raised concerns about the management of severe infections. Here, we describe the post-COVID-19 pandemic re-emergence in Mpn in Ontario, Canada. Despite high case numbers detected in 2024, infections were not more severe than in pre-pandemic years (2018–2019). Mpn genotype ratios and macrolide resistance rates were statistically comparable between 2018/2019 and 2024, suggesting re-emergence of previously circulating strains rather than the introduction of a novel hypervirulent strain.

Influenza A(H3N2) subclade K virus was detected in Canada early in the 2025/26 influenza season, bearing an antigenic transition in the hemagglutinin (HA) glycoprotein. Analysis of 396 HA sequences from Canada showed antigenic divergence from 2025/26 influenza vaccine strains, consistent with partial mismatch. Phylodynamic analysis revealed sustained pre-vaccine transmission without clear post-vaccine expansion. Phylogenetic and phylogeographic analyses indicated interprovincial mixing within a highly connected metapopulation, highlighting the value of genomic surveillance for real-time epidemiologic inference and public health decision-making.

Candida glabrata ( Nakaseomyces glabratus ) is an important cause of invasive fungal infections and may exhibit reduced susceptibility toward antifungal drugs. Here, we used whole-genome sequencing to investigate the genomic phylogeny and identify genetic determinants of antifungal resistance in a collection of 142 clinical C. glabrata isolates obtained from the 10 provinces of Canada between 2013 and 2020. Our study prioritized resistant isolates ( n = 62, 43.7%) from invasive infections to better understand antifungal resistance and represents the largest national genomic survey of clinical C. glabrata isolates performed to date in Canada. Phylogenomic analysis based on single-nucleotide variants in the core genome revealed 15 genetically related clusters of C. glabrata . The largest cluster (cluster I, n = 29) was significantly associated with antifungal resistance ( P value = 0.0112). Antifungal-resistant isolates were present in almost all clusters, suggesting that resistance most likely arises from selective pressure during antifungal therapy, rather than dissemination of resistant clones. Thirty-six unique PDR1 variants were found in 38/52 (73.1%) fluconazole-resistant C. glabrata isolates, with more than half identified in this study as potential novel azole resistance variants. Well-characterized hot-spot variants in FKS genes ( n = 5) were found in 12/13 (92.3%) micafungin-resistant C. glabrata isolates. Our genomic analysis highlights the diversity in strain types and sheds light on potential genetic mechanisms of resistance in Canadian isolates of C. glabrata . IMPORTANCE: Candida glabrata , also known as Nakaseomyces glabratus , is a type of yeast that can cause infections in individuals with weakened immune systems. Invasive infections can be difficult to treat since some C. glabrata isolates may not respond well to common antifungals. We studied a large collection of C. glabrata isolates collected from across Canada to better understand how C. glabrata spreads and why this fungal pathogen sometimes resists treatment. Using whole-genome sequence analysis, we found that drug resistance appears in different strains independently, likely as a result of treatment, rather than spreading from a single clone. We also identified specific mutations that may be linked to resistance to commonly used antifungal drugs, such as fluconazole and micafungin. Our research shows how valuable whole-genome sequencing is for understanding the spread and drug resistance of C. glabrata , which can help improve treatment and infection control.

Diphtheria remains a major public health threat in areas of the world where diphtheria toxoid-containing vaccine programs are not successfully implemented or maintained. In countries with high vaccine coverage, diphtheria is well-controlled with occasional travel-related cases eliciting a robust public health response to limit transmission. While classic diphtheria is caused by toxigenic Corynebacterium diphtheriae and rarely by other species, such as Corynebacterium ulcerans , infections due to nontoxigenic C. diphtheriae (not covered by the vaccine) are increasingly being reported. We describe the genomic epidemiology of toxigenic and nontoxigenic C. diphtheriae in Ontario, Canada, based on isolates submitted to the Public Health Ontario Laboratory. Of 146 cases, four cases (2.7%) involved toxigenic C. diphtheriae , three of which were associated with travel from endemic countries. Most isolates were nontoxigenic (97.2%) and from cutaneous sources (84.9%), with an increase in submission of nontoxigenic C. diphtheriae isolates from one in 2016 to 65 in 2023. Based on whole-genome sequencing and BIGSdb-Pasteur core genome multi-locus strain typing, most nontoxigenic isolates were categorized into three highly related genetic clusters from sublineages 32 and 76, suggesting epidemiologically linked cases indicative of local transmission. Apart from intermediate susceptibility to penicillin in 98.0% of isolates, antimicrobial resistance was rarely detected. Because infections with nontoxigenic C. diphtheriae are not prevented by vaccination and do not cause classic diphtheria, healthcare professionals should be aware of these trends, given the clinical, public health, and infection control implications when C. diphtheriae is identified in the microbiology laboratory prior to knowledge of toxigenicity. IMPORTANCE: Infections by toxigenic and nontoxigenic Corynebacterium diphtheriae cause vastly different diseases requiring different treatment and public health responses. Healthcare practitioners should be aware of the complexities of diphtheria from a global perspective. Toxigenic C. diphtheriae remains prevalent in regions that do not have well-established vaccination programs, while vaccine hesitancy and compliance issues challenge countries that do require childhood vaccination. These factors, coupled with the propensity for human travel and migration, heighten the risk of cases and outbreaks in non-endemic countries and designate diphtheria as a relevant re-emerging threat. Further complicating public health decisions is the increasing incidence of nontoxigenic C. diphtheriae infections identified among highly vaccinated populations. An excessive public health response in these cases would be burdensome and expensive. Our findings will aid public health departments and hospitals with local risk assessments of the likelihood that a laboratory identification of C. diphtheriae represents a case of toxigenic diphtheria by raising awareness of the disproportionately small number of toxigenic C. diphtheriae recovered from clinical specimens compared to the vast majority of nontoxigenic isolates. Genomic analysis suggests local transmission of nontoxigenic strains, while isolation of toxigenic C. diphtheriae from among a highly vaccinated population remains associated with travel to endemic regions.

Objective: To assess preparedness for Candida auris in Canadian hospitals. Design: Cross-sectional survey. Setting: Canadian Nosocomial Infection Surveillance Program (CNISP) hospitals. Methods: In June 2024, surveys were e-mailed to the infection prevention and control departments of 109 CNISP hospitals and their 33 microbiology laboratories. The surveys assessed policies for patient screening/management and laboratory processes supporting C. auris transmission prevention. Results were compared to a similar 2018 survey. Results: All 109 hospitals and 32/33 laboratories responded. Most hospitals had policies for admission screening (80%, 87/109) and policies/defined plans for post-exposure screening (95%, 104/109). Policy presence increased from 18% to 73% in 56 hospitals completing both 2018 and 2024 surveys ( P < 0.001). Among hospitals with admission screening policies, 69% (60/87) screened for recent out-of-country hospitalization. All but one hospital implemented transmission-based precautions for cases; 70% (76/109) continued precautions indefinitely. Overall, 94% (99/105; excluding hospitals with exclusively private rooms) and 55% (60/109) of hospitals screened roommates and wardmates, respectively. Frequency and timing of screening and policies regarding precautions for exposed patients varied. All hospitals used axilla and groin swabs, at minimum, for screening. Most (81%, 26/32) laboratories identified all clinically significant Candida isolates to species level, increasing from 48% to 85% ( P < 0.001) in the 27 laboratories completing both 2018 and 2024 surveys. Twenty-four laboratories (75%) had standard operating procedures for processing screening specimens; 96% (23/24) used direct plating onto chromogenic agar. Conclusions: Despite progress in C. auris preparedness, areas for improvement remain. Variability in practice may be related to evidence gaps and resource constraints.

In the last 15 years, advances in diagnostic microbiology have enabled more detailed characterization of human bacterial pathogens. These changes have led to the description of new species within the Staphylococcus aureus complex, including S. aureus subspecies anaerobius , Staphylococcus argenteus , and Staphylococcus schweitzeri . In this minireview, we discuss the history, epidemiology, microbiology, genomics, and clinical significance of the S. aureus complex and provide a guide for laboratories to reliably detect and differentiate these novel species.