Impact of KPC Production and High-Level Meropenem Resistance on All-Cause Mortality of Ventilator-Associated Pneumonia in Association with Klebsiella pneumoniae.

Carbapenemase-producing Enterobacterales and specifically Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae (KPC-Kp) are rapidly spreading worldwide. The prognosis of ventilator-associated pneumonia (VAP) caused by KPC-Kp is not well known. Our study tries to assess whether ventilator-associated pneumonia caused by a KPC-Kp strain is associated with higher all-cause mortality than that caused by carbapenem-susceptible isolates. This is a retrospective cohort study of patients with VAP due to K. pneumoniae from a 35-bed polyvalent intensive care unit in a university hospital (>40,000 annual admissions) between January 2012 and December 2016. Adjusted multivariate analysis was used to study the association of KPC-Kp with 30-day all-cause mortality (Cox regression). We analyze 69 cases of K. pneumoniae VAP, of which 39 were produced by a KPC-Kp strain with high-level resistance to meropenem (MIC > 16 mg/ml). All-cause mortality at 30 days was 41% in the KPC-Kp group (16/39) and 33.3% in the carbapenem-susceptible cases (10/30). KPC-Kp etiology was not associated with higher mortality when controlled for confounders (adjusted hazard ratio [HR], 1.25; 95% confidence interval [CI], 0.46 to 3.41). Adequate targeted therapy (HR, 0.03; 95% CI, <0.01 to 0.23) was associated with all-cause mortality. Assuming the limitations due to the available sample size, the prognosis of VAP caused by KPC-Kp is similar to VAPs caused by carbapenem-susceptible K. pneumoniae when appropriate treatment is used.

Comparative study of in vitro activity of tedizolid and linezolid against Mycobacterium avium complex.

OBJECTIVES: The aim of this study is to compare the in vitro activity and minimal inhibitory concentration (MIC) distributions of tedizolid and linezolid against Mycobacterium avium complex (MAC) strains using a reference broth microdilution assay and a macrodilution assay with the Bactec-MGIT-960. METHODS: A total of 37 clinical isolates of MAC were included in the study. Reference broth microdilution was performed according to CLSI guidelines in a range of concentrations from 64 to 0.064 mg/L. Macrodilution was performed with the Bactec-MGIT-960 system. The cut-off points defined by CLSI for linezolid (resistant: > 16 mg/L, intermediate: 16 mg/L, susceptible: <16 mg/L) were used to define clinical categories of this drug. Essential agreement for both linezolid and tedizolid and categorical agreement for linezolid were defined following FDA criteria. RESULTS: The MIC50 (16mg/L) and MIC90 (32mg/L) values for linezolid were identical with both methods. However, the MIC50 and MIC90 of tedizolid by microdilution (4 mg/L and 8 mg/L, respectively) were one twofold dilution higher than by macrodilution (2 mg/L and 4 mg/L, respectively). Ninety-four percent and 2.7% of the strains had MICs of tedizolid ≤4 mg/L and ≤ 0.5 mg/L, respectively, by the reference method. The linezolid macrodilution assay showed a categorical agreement of 40.5%, a minor error rate of 56.7% and a major error rate of 2.7% with respect to the reference method. CONCLUSIONS: Tedizolid showed higher in vitro activity than linezolid against the tested MAC isolates. Macrodilution using the BD Bactec-MGIT-960 system is a practical approach to determine the susceptibility of MAC strains to tedizolid.

Sample pooling for SARS-CoV-2 RT-PCR screening.

OBJECTIVE: To evaluate the efficacy of sample pooling compared to the individual analysis for the diagnosis of coronavirus disease 2019 (COVID-19) by using different commercial platforms for nucleic acid extraction and amplification. METHODS: A total of 3519 nasopharyngeal samples received at nine Spanish clinical microbiology laboratories were processed individually and in pools (342 pools of ten samples and 11 pools of nine samples) according to the existing methodology in place at each centre. RESULTS: We found that 253 pools (2519 samples) were negative and 99 pools (990 samples) were positive; with 241 positive samples (6.85%), our pooling strategy would have saved 2167 PCR tests. For 29 pools (made out of 290 samples), we found discordant results when compared to their correspondent individual samples, as follows: in 22 of 29 pools (28 samples), minor discordances were found; for seven pools (7 samples), we found major discordances. Sensitivity, specificity and positive and negative predictive values for pooling were 97.10% (95% confidence interval (CI), 94.11-98.82), 100%, 100% and 99.79% (95% CI, 99.56-99.90) respectively; accuracy was 99.80% (95% CI, 99.59-99.92), and the kappa concordant coefficient was 0.984. The dilution of samples in our pooling strategy resulted in a median loss of 2.87 (95% CI, 2.46-3.28) cycle threshold (Ct) for E gene, 3.36 (95% CI, 2.89-3.85) Ct for the RdRP gene and 2.99 (95% CI, 2.56-3.43) Ct for the N gene. CONCLUSIONS: We found a high efficiency of pooling strategies for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA testing across different RNA extraction and amplification platforms, with excellent performance in terms of sensitivity, specificity and positive and negative predictive values.