Background: Extended-spectrum β-lactamase (ESBL)-producing Escherichia coli is among the most important multidrug-resistant pathogens causing bloodstream infections (BSIs).Cefotaximase (CTX-M) enzymes are the most common and highly diverse ESBL family in E.coli. CTX-M-15 in group CTX-M-1 and CTX-M-14 in group CTX-M-9 are the most extensively disseminated enzymes. Multidrug-resistant E. coli strains complicate empirical therapy and increase healthcare burden globally and in Korea. We investigated the molecular epidemiology, sequence types (STs), and ESBL genotypes of E. coli bloodstream isolates in Korea and identified clinical risk factors for cefotaxime resistance. Methods: We collected all non-duplicated isolates of E. coli and related clinical information from patients with BSIs at eight sentinel hospitals in the Korean Global Antimicrobial Resistance Surveillance System (Kor-GLASS) collection network during 2017–2021. Duplicate isolates were removed to ensure representativeness of the data. Antimicrobial susceptibility was tested using disk diffusion tests, and multilocus sequence typing and betalactamase genotyping were performed. Results: Among 9,232 E. coli blood isolates, resistance rates to cefotaxime and ceftazidime were 36.4% and 11.4%, respectively. Among the clinical factors, age > 65 yrs (adjusted odds ratio [aOR], 1.36), hospital-origin infection (aOR, 2.55), and admission type (intensive care unit [ICU] vs. general ward; aOR, 1.34) were significant cefotaxime resistance risk factors. ST131 was the most prevalent among cefotaxime-resistant E. coli (64.8%, 2,180/3,363), followed by ST1193 (5.3%, N = 177), and ST69 (5.1%, N = 170).ST131, ST648, ST405, and ST410 cefotaxime-resistant E. coli isolates frequently harbored blaCTX-M-15, whereas ST1193 and ST68 showed a high proportion of blaCTX-M-27 carriers, and most ST457 and ST5150 isolates carried blaCTX-M-55. Conclusions Continuous monitoring of ESBL-producing E. coli is required to prevent further dissemination, guide empirical therapy, inform infection control policies, and ensure early detection of multidrug-resistant clones with the potential for widespread transmission.

Enterococcus faecium, particularly in its multidrug-resistant forms, causes invasive nosocomial infections. Given the limited data comparing the effectiveness of the European Committee on Antimicrobial Susceptibility Testing (EUCAST) and the CLSI clinical breakpoints (CBPs) for quinupristin–dalfopristin (QD) resistance and the need to evaluate their practical application, we retrospectively investigated the susceptibility patterns of 287 E.faecium bloodstream isolates from Korean hospitals to QD using the updated EUCAST and CLSI CBPs and two antimicrobial susceptibility testing methods: disk diffusion (DD) and Sensititre broth microdilution (Sensititre). QD resistance rates were 5.9% (CLSI) and 18.8% (EUCAST) for DD and 22.6% (CLSI) and 28.2% (EUCAST) for Sensititre. The most prevalent QD resistance gene types among QD-resistant isolates were ermB+msrC+ or ermB– msrC+. Categorical agreement between DD and Sensititre ranged from 77.7% to 90.7%, depending on the testing method and CBPs applied. The EUCAST zone diameter CBPs more effectively help identify QD-resistant E. faecium isolates using the DD method than the CLSI zone diameter CBPs. In comparison, the CLSI minimum inhibitory concentration (MIC) CBPs provide more reliable results for resistance classification in the Sensititre method than EUCAST MIC CBPs. These findings would help improve clinical decision-making for treating multidrug-resistant E. faecium infections.

Background: Haemophilus influenzae is the causative pathogen for various infectious diseases, such as respiratory infections, otitis media, sinusitis, and meningitis. This study aimed to investigate the prevalence and molecular characteristics of β-lactam resistance in non-typeable H. influenzae isolates in South Korea. Methods: In total, 115 non-duplicated H. influenzae isolates were included in this study.Bacterial identification and serotyping were performed using matrix assisted laser desorption ionization-time of flight mass spectrometry and polymerase chain reaction (PCR) of bexA, respectively. Antimicrobial susceptibility was tested using the broth microdilution method.The production of β-lactamase was determined using nitrocefin disks. The presence of blaTEM and blaROB was confirmed using PCR. ftsI was analyzed to identify amino acid mutations in penicillin-binding protein (PBP) 3. Results: Resistance rates to ampicillin, amoxicillin–clavulanate, and cefuroxime were 67.8%, 13.9%, and 32.2%, respectively. None of the isolates were resistant to cefotaxime or ceftriaxone. Among 78 ampicillin-resistant isolates, 71 were β-lactamase-producing ampicillinresistant (BLPAR), and 7 were β-lactamase-non-producing ampicillin-resistant. All BLPAR isolates carried blaTEM, and none carried blaROB. Among 16 amoxicillin–clavulanate-resistant isolates, 15 β-lactamase producers harbored blaTEM. Four to 7 PBP3 mutations per isolate were detected in all 16 non-β-lactamase-producing ampicillin-resistant or cephalosporinresistant isolates. Conclusion Beta-lactam resistance in non-typeable H. influenzae isolates is highly prevalent in South Korea, primarily because of blaTEM and various PBP3 mutations. Therefore, continuous monitoring of antimicrobial resistance rates and mechanisms in non-typeable H.influenzae is necessary.

Background: The life expectancy of people living with human immunodeficiency virus (PLWH) has significantly improved with advancements in antiretroviral therapy (ART). However, aging PLWH face a growing burden of noncommunicable diseases (NCDs), polypharmacy, and drug-drug interactions (DDIs), which pose challenges in their management. This study investigates the prevalence of NCDs, polypharmacy, and DDIs among PLWH aged ≥50 years in Korea and their impact on quality of life (QOL). Materials and Methods: A cross-sectional study was conducted among 243 PLWH aged ≥50 years receiving ART for at least three months at three university hospitals in Korea between January and July 2022. Data were collected through electronic medical records and personal interviews, assessing demographics, comorbidities, polypharmacy, ART adherence, and QOL using the Korean version of WHOQOL-HIV BREF scale. Potential DDIs were analyzed using the University of Liverpool HIV Drug Interaction Database, and potentially inappropriate medications (PIMs) were identified using the 2023 American Geriatrics Society Beers Criteria. We classified participants into three age groups:50–<65 years, 65–<75 years, and ≥75 years. Results: The prevalence of comorbidities was 71.6%, with older participants (≥75 years) showing a significantly higher burden, including bone diseases, osteoarthritis, and dementia (P<0.001). Polypharmacy was observed in 28.4% of participants and increased with age, with 53.3% of those aged ≥75 years taking ≥10 pills daily.Polypharmacy was associated with poorer QOL (71.6 vs. 76.6, P=0.010). Amber-flag DDIs were found in 81 participants (33.3%), most commonly involving metformin and divalent cations. No red-flag DDIs were identified.PIMs were observed in 6.6% of participants aged ≥65 years. Conclusion Aging PLWH in Korea face significant challenges from comorbidities, polypharmacy, and DDIs, which negatively impact QOL. Integrated, age-specific, and multidisciplinary care strategies are urgently needed to improve outcomes and ensure the well-being of older PLWH.

Background: The life expectancy of people living with human immunodeficiency virus (PLWH) has significantly improved with advancements in antiretroviral therapy (ART). However, aging PLWH face a growing burden of noncommunicable diseases (NCDs), polypharmacy, and drug-drug interactions (DDIs), which pose challenges in their management. This study investigates the prevalence of NCDs, polypharmacy, and DDIs among PLWH aged ≥50 years in Korea and their impact on quality of life (QOL). Materials and Methods: A cross-sectional study was conducted among 243 PLWH aged ≥50 years receiving ART for at least three months at three university hospitals in Korea between January and July 2022. Data were collected through electronic medical records and personal interviews, assessing demographics, comorbidities, polypharmacy, ART adherence, and QOL using the Korean version of WHOQOL-HIV BREF scale. Potential DDIs were analyzed using the University of Liverpool HIV Drug Interaction Database, and potentially inappropriate medications (PIMs) were identified using the 2023 American Geriatrics Society Beers Criteria. We classified participants into three age groups:50–<65 years, 65–<75 years, and ≥75 years. Results: The prevalence of comorbidities was 71.6%, with older participants (≥75 years) showing a significantly higher burden, including bone diseases, osteoarthritis, and dementia (P<0.001). Polypharmacy was observed in 28.4% of participants and increased with age, with 53.3% of those aged ≥75 years taking ≥10 pills daily.Polypharmacy was associated with poorer QOL (71.6 vs. 76.6, P=0.010). Amber-flag DDIs were found in 81 participants (33.3%), most commonly involving metformin and divalent cations. No red-flag DDIs were identified.PIMs were observed in 6.6% of participants aged ≥65 years. Conclusion Aging PLWH in Korea face significant challenges from comorbidities, polypharmacy, and DDIs, which negatively impact QOL. Integrated, age-specific, and multidisciplinary care strategies are urgently needed to improve outcomes and ensure the well-being of older PLWH.

During nationwide Fantimicrobial surveillance (Korea Global Antimicrobial Resistance Surveillance System [Kor-GLASS]), the recent emergence of non-oxacillinase (OXA)-23 production by carbapenem-resistant Acinetobacter baumannii (CRAB) isolates was noted. In this study, we evaluated resistance mechanisms other than OXA-23 production to elucidate the shift in considerable CRAB clones. The presence of OXA carbapenemase genes, such as blaOXA-23 , blaOXA-24 , blaOXA-58 , and blaOXA-51-ISAba1, was determined by PCR. Other carbapenemase genes, such as blaIMP , blaVIM , blaNDM , blaKPC , blaGES , and blaOXA-48 , were determined using sequencing. Strains lacking carbapenemase genes were subjected to whole genome sequencing, and resistance genes were analyzed using ResFinder. Four CRAB strains were collected through a Kor-GLASS study in 2022, in which OXA-23 production was not identified. The carbapenemase genotypes of the four CRAB strains lacking blaOXA-23 were blaOXA-51 -ISAba1, blaOXA-66/ACD25 , blaOXA-182, and blaNDM-1 . To the best of our knowledge, this is the first study to identify CRAB producing New Delhi metallo-β-lactamase (NDM)-1 in Korea. In conclusion, domestic CRAB resistance mechanisms may undergo subtle changes. Continuous observations are required to monitor the emergence of new clones.

This study was conducted to investigate potential differences in vaccine efficacy between patients undergoing palliative chemotherapy and receiving adjuvant chemotherapy. Additionally, the study proved the influence of vaccination timing on vaccine efficacy during active chemotherapy. Anti-receptor-binding domain (RBD) IgG binding antibody assays and surrogate neutralizing antibody assays were performed after BNT162b2 or mRNA-1273 vaccination in 45 solid cancer patients (23 adjuvant and 22 palliative chemotherapy) and in 24 healthy controls before vaccination (baseline), at every two to four weeks after the first (post-dose 1) and the second vaccination (post-dose 2). The levels of anti-RBD IgG and neutralizing antibodies increased significantly from baseline through post-dose 1 to post-dose 2 in all three groups. At the post-dose 1, the anti-RBD IgG and neutralizing antibody levels were significantly lower in cancer patients than in healthy controls. However, by post-dose 2, the seropositivity of anti-RBD IgG and neutralizing antibodies uniformly reached 100% across all groups, with no significant disparity in antibody levels among the three groups. Moreover, the antibody titers were not significantly different between patients with a vaccine and chemotherapy interval of more than 14 days or those with less than 14 days. This study demonstrated that after second doses of mRNA COVID-19 vaccines, humoral immune responses in patients receiving chemotherapy were comparable to those of healthy controls, regardless of whether the purpose of the anti-cancer treatment was palliative or adjuvant. Furthermore, the timing of vaccination did not affect the level of humoral immunity after the second vaccination.

Background: Since the emergence of hypervirulent strains of Clostridioides difficile, the incidence of C. difficile infections (CDI) has increased significantly. Methods: To assess the incidence of CDI in Korea, we conducted a prospective multicentre observational study from October 2020 to October 2021. Additionally, we calculated the incidence of CDI from mass data obtained from the Health Insurance Review and Assessment Service (HIRA) from 2008 to 2020. Results: In the prospective study with active surveillance, 30,212 patients had diarrhoea and 907 patients were diagnosed with CDI over 1,288,571 patient-days and 193,264 admissions in 18 participating hospitals during 3 months of study period; the CDI per 10,000 patientdays was 7.04 and the CDI per 1,000 admission was 4.69. The incidence of CDI was higher in general hospitals than in tertiary hospitals: 6.38 per 10,000 patient-days (range: 3.25–12.05) and 4.18 per 1,000 admissions (range: 1.92–8.59) in 11 tertiary hospitals, vs. 9.45 per 10,000 patient-days (range: 5.68–13.90) and 6.73 per 1,000 admissions (range: 3.18–15.85) in seven general hospitals. With regard to HIRA data, the incidence of CDI in all hospitals has been increasing over the 13-year-period: from 0.3 to 1.8 per 10,000 patient-days, 0.3 to 1.6 per 1,000 admissions, and 6.9 to 56.9 per 100,000 population, respectively. Conclusion The incidence of CDI in Korea has been gradually increasing, and its recent value is as high as that in the United State and Europe. CDI is underestimated, particularly in general hospitals in Korea.

Background: The life expectancy of people living with human immunodeficiency virus (PLWH) has significantly improved with advancements in antiretroviral therapy (ART). However, aging PLWH face a growing burden of noncommunicable diseases (NCDs), polypharmacy, and drug-drug interactions (DDIs), which pose challenges in their management. This study investigates the prevalence of NCDs, polypharmacy, and DDIs among PLWH aged ≥50 years in Korea and their impact on quality of life (QOL). Materials and Methods: A cross-sectional study was conducted among 243 PLWH aged ≥50 years receiving ART for at least three months at three university hospitals in Korea between January and July 2022. Data were collected through electronic medical records and personal interviews, assessing demographics, comorbidities, polypharmacy, ART adherence, and QOL using the Korean version of WHOQOL-HIV BREF scale. Potential DDIs were analyzed using the University of Liverpool HIV Drug Interaction Database, and potentially inappropriate medications (PIMs) were identified using the 2023 American Geriatrics Society Beers Criteria. We classified participants into three age groups:50–<65 years, 65–<75 years, and ≥75 years. Results: The prevalence of comorbidities was 71.6%, with older participants (≥75 years) showing a significantly higher burden, including bone diseases, osteoarthritis, and dementia (P<0.001). Polypharmacy was observed in 28.4% of participants and increased with age, with 53.3% of those aged ≥75 years taking ≥10 pills daily.Polypharmacy was associated with poorer QOL (71.6 vs. 76.6, P=0.010). Amber-flag DDIs were found in 81 participants (33.3%), most commonly involving metformin and divalent cations. No red-flag DDIs were identified.PIMs were observed in 6.6% of participants aged ≥65 years. Conclusion Aging PLWH in Korea face significant challenges from comorbidities, polypharmacy, and DDIs, which negatively impact QOL. Integrated, age-specific, and multidisciplinary care strategies are urgently needed to improve outcomes and ensure the well-being of older PLWH.

Background: The epidemiology of pathogenic bacteria varies according to the socioeconomic status and antimicrobial resistance status. However, longitudinal epidemiological studies to evaluate the changes in species distribution and antimicrobial susceptibility of pathogenic bacteria nationwide are lacking. We retrospectively investigated the nationwide trends in species distribution and antimicrobial susceptibility of pathogenic bacteria over the last 20 years in Korea. Methods: From 1997 to 2016, annual cumulative antimicrobial susceptibility and species distribution data were collected from 12 university hospitals in five provinces and four metropolitan cities in South Korea. Results: The prevalence of Staphylococcus aureus was the highest (13.1%) until 2012 but decreased to 10.3% in 2016, consistent with the decrease in oxacillin resistance from 76.1% in 2008 to 62.5% in 2016. While the cefotaxime resistance of Escherichia coli increased from 9.0% in 1997 to 34.2% in 2016, E. coli became the most common species since 2013, accounting for 14.5% of all isolates in 2016. Pseudomonas aeruginosa and Acinetobacter baumannii rose to third and fifth places in 2008 and 2010, respectively, while imipenem resistance increased from 13.9% to 30.8% and 0.7% to 73.5% during the study period, respectively.Streptococcus agalactiae became the most common pathogenic streptococcal species in 2016, as the prevalence of Streptococcus pneumoniae decreased since 2010. During the same period, pneumococcal penicillin susceptibility decreased to 79.0%, and levofloxacin susceptibility of S. agalactiae decreased to 77.1% in 2016. Conclusion The epidemiology of pathogenic bacteria has changed significantly over the past 20 years according to trends in antimicrobial resistance in Korea. Efforts to confine antimicrobial resistance would change the epidemiology of pathogenic bacteria and, consequently, the diagnosis and treatment of infectious diseases.