Clinical and Genomic Characterization of a Cohort of Patients With Klebsiella pneumoniae Bloodstream Infection.

BACKGROUND: The clinical and microbial factors associated with Klebsiella pneumoniae bloodstream infections (BSIs) are not well characterized. Prior studies have focused on highly resistant or hypervirulent isolates, limiting our understanding of K. pneumoniae strains that commonly cause BSI. We performed a record review and whole-genome sequencing to investigate the clinical characteristics, bacterial diversity, determinants of antimicrobial resistance, and risk factors for in-hospital death in a cohort of patients with K. pneumoniae BSI. METHODS: We identified 562 patients at Massachusetts General Hospital with K. pneumoniae BSIs between 2016 and 2022. We collected data on comorbid conditions, infection source, clinical outcomes, and antibiotic resistance and performed whole-genome sequencing on 108 sequential BSI isolates from 2021 to 2022. RESULTS: Intra-abdominal infection was the most common source of infection accounting for 34% of all BSIs. A respiratory tract source accounted for 6% of BSIs but was associated with a higher in-hospital mortality rate (adjusted odds ratio, 5.4 [95% confidence interval, 2.2-12.8]; P < .001 for comparison with other sources). Resistance to the first antibiotic prescribed was also associated with a higher risk of death (adjusted odds ratio, 5.2 [95% confidence interval, 2.2-12.4]; P < .001). BSI isolates were genetically diverse, and no clusters of epidemiologically and genetically linked cases were observed. Virulence factors associated with invasiveness were observed at a low prevalence, although an unexpected association between O-antigen type and the source of infection was found. CONCLUSIONS: These observations demonstrate the versatility of K. pneumoniae as an opportunistic pathogen and highlight the need for new approaches for surveillance and the rapid identification of patients with invasive antimicrobial-resistant K. pneumoniae infection.

Multiplexed real-time PCR for the detection and differentiation of Klebsiella pneumoniae O-antigen serotypes.

Klebsiella pneumoniae has emerged as a global health threat due to its role in the spread of antimicrobial resistance and because it is a frequent cause of hospital-acquired infections and neonatal sepsis. Capsular and lipopolysaccharide (LPS) O-antigen polysaccharide surface antigens are major immunogens that are useful for strain classification and are candidates for vaccine development. We have developed real-time PCR reagents for molecular serotyping, subtyping, and quantitation of the most prevalent LPS O-antigen types (i.e., O1, O2, O3, and O5) of Klebsiella pneumoniae. We describe two applications for this O-typing assay: for screening culture isolates and for direct typing of Klebsiella pneumoniae present in stool samples. We find 100% concordance between the results of the O-typing assay and whole-genome sequencing of 81 culture isolates, and >90% agreement in O-typing performed directly on specimens of human stool, with disagreement arising primarily from a lack of sensitivity of the culture-based comparator method. Additionally, we find evidence for mixed O-type populations at varying levels of abundance in direct tests of stool from a hospitalized patient population. Taken together, these results demonstrate that this novel O-typing assay can be a useful tool for K. pneumoniae epidemiologic and vaccine studies.IMPORTANCEKlebsiella pneumoniae is an important opportunistic pathogen. The gastrointestinal (GI) tract is the primary reservoir of K. pneumoniae in humans, and GI carriage is believed to be a prerequisite for invasive infection. Knowledge about the dynamics and duration of GI carriage has been hampered by the lack of tools suitable for detection and strain discrimination. Real-time PCR is particularly suited to the higher-throughput workflows used in population-based studies, which are needed to improve our understanding of carriage dynamics and the factors influencing K. pneumoniae colonization.

Identifying Recent Cholera Infections Using a Multiplex Bead Serological Assay.

Estimates of incidence based on medically attended cholera can be severely biased. Vibrio cholerae O1 leaves a lasting antibody signal and recent advances showed that these can be used to estimate infection incidence rates from cross-sectional serologic data. Current laboratory methods are resource intensive and challenging to standardize across laboratories. A multiplex bead assay (MBA) could efficiently expand the breadth of measured antibody responses and improve seroincidence accuracy. We tested 305 serum samples from confirmed cholera cases (4 to 1083 d postinfection) and uninfected contacts in Bangladesh using an MBA (IgG/IgA/IgM for 7 Vibrio cholerae O1-specific antigens) as well as traditional vibriocidal and enzyme-linked immunosorbent assays (2 antigens, IgG, and IgA). While postinfection vibriocidal responses were larger than other markers, several MBA-measured antibodies demonstrated robust responses with similar half-lives. Random forest models combining all MBA antibody measures allowed for accurate identification of recent cholera infections (e.g., past 200 days) including a cross-validated area under the curve (cvAUC200) of 92%, with simpler 3 IgG antibody models having similar accuracy. Across infection windows between 45 and 300 days, the accuracy of models trained on MBA measurements was non-inferior to models based on traditional assays. Our results illustrated a scalable cholera serosurveillance tool that can be incorporated into multipathogen serosurveillance platforms. IMPORTANCE Reliable estimates of cholera incidence are challenged by poor clinical surveillance and health-seeking behavior biases. We showed that cross-sectional serologic profiles measured with a high-throughput multiplex bead assay can lead to accurate identification of those infected with pandemic Vibrio cholerae O1, thus allowing for estimates of seroincidence. This provides a new avenue for understanding the epidemiology of cholera, identifying priority areas for cholera prevention/control investments, and tracking progress in the global fight against this ancient disease.