Study design and setting
We conducted a single center retrospective case-control study of COVID-19 patients admitted to the ICUs of Erasme Hospital, Brussels, Belgium from March to April 2020. The ethics committee approved this study (P2020/371) and waived the need for an informed consent.
Under normal circumstances, our ICU operates with 30 beds divided into five ICUs with 6-single rooms each. We perform nasal and rectal surveillance cultures upon ICU admission and twice a week thereafter. Colonization by MRSA, ESBL, CPE and VRE is indicated at the room door and requires health care workers to wear gloves and gown before entry. We have a meeting with the antibiotic stewardship team twice a week.
COVID-19 crisis management
During COVID-19 crisis, we increased our ICU beds from 30 to 39, by opening 5 beds in the existing ICUs and building another 4-beds ICU in two operating rooms. Only one 6-beds ICU remained available for non-COVID-19 admissions. The remaining 33 beds were reserved for COVID-19 patients with a high risk of invasive mechanical ventilation. Patients with stable clinical condition on CPAP remained in the wards.
Patients’ selection
Cases:
All patients admitted to the COVID-19 ICUs of Erasme Hospital between 15/03 and 30/04, regardless of the final etiological diagnosis, were eligible for inclusion; the sole exclusion criterion was an ICU stay < 48h. These patients were considered as cases and are named COVID-19 patients in this manuscript.
Controls:
The admission to the non-COVID 19 ICU was scarce during the study period. Therefore, it was not possible to use this population as control. Given the unusual duration of mechanical ventilation in COVID-19 patients, [12] we compared them to patients obtained from a preexisting subarachnoid hemorrhage (SAH) institutional database cohort. [13] These patients were admitted to our ICU from January 2016 – 2019. Severe SAH patients are young with few comorbidities and can have prolonged ICU length of stay (LOS) [14] and duration of mechanical ventilation. [15] Patients were matched 1:1 according to ICU LOS and the use of mechanical ventilation. Patients with ICU LOS less than ten days were matched with controls with a difference of ± 2 days, and patients with ICU LOS > 10 days were matched with controls with a ± 20% difference in the LOS. When several controls could match one COVID-19 patient we selected the control with the closest ICU LOS.
Data collection and endpoints:
Demographic data and severity scores were collected at ICU admission. We defined the length of exposure as the duration between ICU admission and the day of MDRB acquisition, or between ICU admission and ICU discharge in patients without MDRB acquisition. We collected the following data during the exposure time: antimicrobial use, presence of central venous catheter, urinary tract catheter, mechanical ventilation and the occurrence of surgery. The primary endpoint was the rate acquisition of MDRB in the COVID 19 units.
Microbiology data:
We considered patients MDRB + when a MDRB was found in any microbiological specimen. Patients that were MDRB+ within 48h after admission were considered index cases. Patients that acquired MDRB during ICU stay were considered new cases. Patients that didn’t acquire MDRB during ICU stay were considered MDRB -. We collected the presence of possible cross-transmission. Cross-transmission was suspected if a patient acquired a MDR pathogen with the same antimicrobial susceptibility and resistance mechanism than another patient hospitalized at the same time in the same unit.
In our center, we perform routine surveillance cultures (rectal swab, tracheal aspirate and urinary cultures) on admission and then twice a week throughout the ICU stay.
For MDRB detection, rectal swabs are streaked onto selective plates as follow: chromID® CARBA SMART agar (bioMérieux, France) for the detection of carbapenemase-producing Enterobacteriaceae; MacConkey agar containing ceftazidime (bioTRADING, Netherlands) for the detection of third generation cephalosporin-resistant Pseudomonas aeruginosa, Klebsiella spp. and Enterobacter spp.; chromID® VRE agar for the detection of Vancomycin-resistant Enterococcus faecium. Identification of MDRB is performed using matrix-assisted-laser desorption ionization-time of flight analysis (MALDI–TOF).
Antimicrobial resistance was defined according to breaking points recommended by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) [16] using VITEK2 and disk diffusion method. Carbapenemases OXA-48, KPC, NDM, VIM and IMP were detected via Polymerase Chain Reaction (PCR) analysis or Coris Resist-5 O.O.K.N.V. antigenic detection (Coris BioConcept, Belgium). VanA and VanB genes were detected via PCR analysis. ESBL-producing Enterobacteriaceae and ampC de-repression were identified using detection of synergy on disk diffusion test as recommended by EUCAST. For methicillin-resistant S.aureus detection, nasopharyngeal swabs were streaked onto ChromID® MRSA selective plates. MDR Pseudomonas and Acinetobacter spp. were defined as recommended considering antimicrobial resistance phenotype. [17]
Statistical analysis:
Categorical variables are reported as count (%), continuous data that were normally distributed as mean ± standard deviation (SD) and skewed data as median [interquartile range].
Incidence of MDRB acquisition was calculated by dividing the number of new cases by the total number of patients admitted to the COVID-19 ICUs. The incidence rate was calculated by dividing the number of new cases by the total number of patient-days in the COVID-19 ICUs. We compared MDRB+ and MDRB – patients in the COVID 19 cohort using Student’s T-test, Mann-Whitney test, χ² test or Fisher’s exact test, as appropriate. In order to identify factors associated with the acquisition of MDRB, we compared patients admitted to COVID 19 ICUs with SAH patients admitted to our ICUs in previous years (2016-2019). Cumulative incidence function of the acquisition of MDRB was used to describe the probability of MDRB acquisition at a given time. The Gray’s test was used to test for the differences. Univariate and multivariable regression analyses were performed using the Fine and Gray competing risks proportional hazards regression model. Death was considered as a competing risk factor for the development of MDRB. In the multivariable model only variables that had p-value less than 0.2 by univariate analysis were considered.
All tests were two-tailed and a p value<0.05 was considered as statistically significant. Data were analyzed using IBM® SPSS® Statistics software, version 26 for Macintosh (IBM, Armonk, NY).