Psittacosis is a zoonotic disease caused by Chlamydophila psittaci. The most common presentation is atypical pneumonia. Three cases of pneumonia of varying severity due to psittacosis are described. All patients had a history of avian contact. The diagnosis was confirmed by molecular detection of Chlamydophila psittaci in respiratory specimens. The cases showed good recovery with doxycycline treatment. Increased awareness of psittacosis can shorten diagnostic delay and improve patient outcomes.

Initial cases of COVID-19 reported in Hong Kong were mostly imported from China. However, most cases reported in February 2020 were locally-acquired infections, indicating local community transmissions. We extracted the demographic, clinical and epidemiological data from 50 COVID-19 patients, who accounted for 53.8% of the cases in Hong Kong by February 2020. Whole-genome sequencing of the SARS-CoV-2 were conducted to determine the phylogenetic relatedness and transmission dynamics. Only three (6.0%) patients required ICU admission. Phylogenetic analysis identified six transmission clusters. All locally-acquired cases harboured a common mutation Orf3a G251V and were clustered in two subclades in global phylogeny of SARS-CoV-2. The estimated time to the most recent common ancestor of local COVID-2019 outbreak was December 24, 2019 with an evolutionary rate of 3.04×10 ⁻³ substitutions per site per year. The reproduction number value was 1.84. Social distancing and vigilant epidemiological control are crucial to the containment of COVID-19 transmission. Article summary lines: A combined epidemiological and phylogenetic analysis of early COVID-19 outbreak in Hong Kong revealed that a SARS-CoV-2 variant with ORF3a G251V mutation accounted for all locally acquired cases, and that asymptomatic carriers could be a huge public health risk for COVID-19 control.

A post-COVID surge of Bordetella pertussis was observed globally. China has reported a high level of macrolide-resistant Bordetella pertussis (MRBP) in recent years; however, the epidemiology of MRBP in Hong Kong remains unknown. We retrieved archived B. pertussis isolates from respiratory samples collected at five regional public hospitals in Hong Kong between 2015 and 2024 and tested their minimum inhibitory concentration (MIC) for macrolides and other non-macrolide antibiotics using the Etest method. All isolates were also subjected to whole genome sequencing for genotypic resistance, Multi-locus Antigen Sequence Typing (MLST) and Multi-locus Variable Number of Tandem Repeat Analysis (MLVA) typing. Twenty-nine isolates of B. pertussis were included in the study. All isolates demonstrating phenotypic macrolide resistance harbored the A2047G mutation while showing low MIC to trimethoprim-sulfamethoxazole, doxycycline, levofloxacin, piperacillin-tazobactam and meropenem. In 2023 and 2024, 100% were MRBP and all belonged to the MT28 clone with the ptxP3 antigenic type. The MRBP isolates in Hong Kong were phylogenetically related to those from mainland China during the same period. There was no obvious correlation between macrolide resistance and clinical presentation, laboratory findings, management and outcome. Phylogenetic analysis suggests that MRBP isolates in Hong Kong and mainland China are closely related.

The MALDI-TOF MS Bruker Biotyper MBT subtyping IVD module enables the early detection of cfiA-positive Bacteroides fragilis (cfiA+ BF) during bacterial identification. However, the relationship between genetic positivity, phenotypic resistance, and clinical outcomes has not been fully elucidated. This retrospective study analyzed B. fragilis isolates from three Hong Kong hospitals between 2021 and 2025 to examine their prevalence and the clinical utility of MALDI-TOF MS in rapid cfiA detection. Antibiotic susceptibility testing, cfiA gene detection using MALDI-TOF MS, and Oxford Nanopore sequencing were performed. Medical records were reviewed, and univariate analyses and multivariate logistic regression were used to identify factors associated with cfiA positivity and 30-day all-cause mortality. Overall, B. fragilis exhibited a high rate of antibiotic resistance. Concomitant resistance to carbapenems and metronidazole was identified in three isolates. Among the 166 isolates, 40 (24.1%) were cfiA-positive. cfiA detection by MALDI-TOF MS showed 100% concordance with the gene sequencing results and correlated strongly with phenotypic carbapenem resistance (Φ = 0.82, p < 0.001 for meropenem; Φ = 0.70, p < 0.001 for ertapenem; Φ = 0.63, p < 0.001 for imipenem). Phylogenetic analysis revealed two distinct clusters corresponding to cfiA status, each exhibiting genetic diversity based on multi-locus sequence typing (MLST). The cfiA+ BF isolates demonstrated high-level phenotypic carbapenem resistance in the presence of upstream insertion sequences. The predominant sequence type (ST) among cfiA+ BF isolates was ST157, and 70% of ST157 isolates harbored IS1187 in the upstream region of cfiA. Gene sequencing also identified other emerging beta-lactamase genes bla_OXA-347 and bla_MUN. The 30-day all-cause mortality following B. fragilis infection was 13.3%, with independent predictors including a high Charlson Comorbidity Index (OR = 1.30; p = 0.02) and the absence of early source control (OR = 4.84; p = 0.03). This study highlights the widespread occurrence of cfiA+ BF in Hong Kong and the clinical significance of rapid cfiA detection. Continuous surveillance is essential to monitor the ongoing threat of antibiotic resistance in B. fragilis.

Mycobacterium tuberculosis (MTB)-related peritonitis is a rare but serious complication in patients receiving maintenance peritoneal dialysis (PD). Early diagnosis is difficult due to the low sensitivity and delayed results of conventional microscopy and culture methods. MTB polymerase chain reaction (PCR) testing in PD effluent is recommended as a diagnostic adjunct, but real-world data remain limited. We conducted a 20-year single-centre retrospective study in a tuberculosis-endemic region to evaluate the diagnostic accuracy and clinical utility of MTB-PCR in PD effluent. Among 372 tests, MTB-PCR demonstrated sensitivity 50%, specificity 100%, negative-predictive value 94.6% and positive-predictive value 100%, using diagnoses based on a composite of clinical and laboratory criteria as the reference standard. Sensitivity showed a numerical trend of improvement from 33.3% with earlier assays to 50–85.7% with newer assays. Of 72 patients with culture-confirmed MTB-PD peritonitis, 13 (18.1%) were diagnosed via MTB-PCR. Compared to those diagnosed by non-PCR methods, MTB-PCR-diagnosed patients had shorter time to anti-tuberculosis treatment initiation (median 8 vs. 22 days, p ≤ 0.001) and shorter hospital stay from presentation to treatment (median 8 vs. 17 days, p = 0.008). They also had a numerically lower rate of PD catheter removal prior to treatment initiation [0/13 (0%) vs. 9/53 patients (17.0%), p = 0.186]. Rates of permanent transfer to haemodialysis and all-cause mortality at 1 year were similar among the two groups. These findings suggest a role for early MTB-PCR testing in suspected MTB-PD peritonitis. Further studies are needed to confirm the findings and optimize diagnostic strategies.

The emergence of carbapenem-resistant non-typhoidal Salmonella species (CR-NTS) has been observed in recent years, causing increasing challenges in the clinical management and control of Salmonella infections. However, CR-NTS had not been comprehensively studied in Hong Kong previously. We retrieved archived non-typhoidal Salmonella isolates demonstrating carbapenem resistance from five public hospitals in Hong Kong during January 2020–June 2025. The isolates were characterised by NG-TEST CARBA-5 and subjected to whole-genome sequencing (WGS) and phylogenetic analysis. Clinical information of CR-NTS cases was also reviewed. Fourteen CR-NTS isolates (0.3%, 14/4404) were identified during the study period. All 13 CR-NTS isolates (one isolate could not be recovered) were NDM (New Delhi metallo-β-lactamase)-positive, with the first case identified in March 2023. WGS revealed six Group B Salmonella monophasic variants of Salmonella enterica serovar Typhimurium ST34 harbouring the bla_NDM-5 gene. The most common plasmid replicon co-present among bla_NDM-5-positive isolates was IncHI2–IncHI2A (63.6%, 7/11). Among cases of CR-NTS in our study, self-limiting gastroenteritis was the most common presentation (84.6%, 11/13); none presented with invasive infections; travel history was present in 7.7% (1/13). Phylogenetic analysis showed the genotypic relatedness of the ST34 isolates identified in Hong Kong to those on the Chinese mainland, with the possibility of local CR-NTS acquisition via imported food sources. Our findings highlighted the importance of a One Health approach to the control of CR-NTS and the need for continuous antimicrobial resistance surveillance of Salmonella spp. in Hong Kong.