Introduction
Multidrug-resistant organisms (MDROs) are bacteria resistant to at least one antibiotic in three or more antimicrobial categories, posing a serious global health threat. Antimicrobial resistance (AMR) leads to increased illness, death, and healthcare costs. Factors such as global travel, overuse of antibiotics, and lack of alternative treatments contribute to the spread of resistant bacteria. Without action, AMR could cause up to 10 million deaths annually by 2050, surpassing cancer.
In hospitals, especially ICUs, MDROs worsen patient outcomes and strain resources. Many ICU patients receive antibiotics, with up to 50% of prescriptions deemed inappropriate. The Zero-Resistance Project, launched in Spain in 2016 at the Albacete General University Hospital, aims to reduce MDROs in ICUs and understand colonisation patterns, including distinctions between ICUs and Resuscitation Units. This study seeks to identify key risk factors for MDRO colonisation upon admission and during hospital stay, guiding prevention efforts.
Methods
This was a descriptive observational study with analytical components, approved by relevant ethics committees in Albacete, Spain. It used data from AGUH’s Preventive Medicine Service between April 2016 and December 2021. Initially, it included patients from the mixed ICU, and from May 2016, also from the Resuscitation Unit. Data collection paused during the peak of the COVID-19 pandemic (March–May 2020) due to ICU overload.
Patients were screened on admission and grouped as colonised or non-colonised based on MDRO presence. Daily assessments identified high-risk individuals using criteria like recent hospital stays, antibiotic use, chronic diseases (e.g., COPD, CKD), or known MDRO history.
Microbiological surveillance targeted common resistant bacteria (e.g., MRSA, MDR-Acinetobacter, CRE), using site-specific swabs (nasal, rectal, etc.). Weekly cultures were done during ICU stays. Preventive isolation was applied to at-risk patients until test results confirmed colonisation status.
Discharge data included infection outcomes and colonisation status. Patients readmitted within 7 days were treated as a single case; otherwise, they were counted anew.
Data was analysed using SPSS version 22. Continuous variables were shown as median (IQR) and categorical ones as n (%). Univariate analysis used the Mann-Whitney U or χ² test to compare colonised vs non-colonised cases. Multivariate logistic regression identified associations between risk factors and colonisation. Variables were included based on univariate significance and clinical relevance. Results were expressed as odds ratios (OR), with p < 0.05 considered statistically significant.
Results
Between April 2016 and December 2021, a total of 7,541 cases admitted to the mixed ICU and Resuscitation Unit at AGUH were analysed, out of 7,783 recorded admissions. A total of 242 cases were excluded due to missing or incomplete colonisation studies. Of the analysed cases, 64.2% were male, with a median age of 63.9 years (IQR: 52.8–73.7), and the median ICU stay was 2 days (IQR: 1–5). Admissions were distributed as 57.6% in the Resuscitation Unit and 42.4% in the mixed ICU. Preventive isolation measures were applied in 30.8% of cases. Risk factors for MDRO colonisation were present in 36.0% of patients, with the most frequent being hospitalisation for 5 or more days in the previous 3 months (19.4%), chronic obstructive pulmonary disease (COPD) (8.6%), and antibiotic use for 7 or more days in the past month (5.9%). Known colonisation or infection by MDROs prior to ICU admission was identified in 4.0% of cases, and no patients with cystic fibrosis were included in the study. Fig. 1 shows the distribution of cases according to risk factors when admitted to units.
The main reason for being discharged from ICUs was being transferred to a ward, which accounted for 86.9 % of cases. Death occurred in 9.4 % of cases and 3.4 % were transferred to another centre. During the initial assessment upon admission to ICUs, 7.5 % of cases were colonised by one MDRO or more. The most commonly identified MDROs were ESBL-producing Enterobacteriaceae, which accounted for 55.7 %, followed by MRSA with 32.5 % (Fig. 2).
Out of 7,541 cases, follow-up colonisation tests after the 7th hospital day were done for 1,308 patients, with 12.5% (163 cases) showing nosocomial MDRO colonisation. Among them, 12 were already initially colonised with a different MDRO. No post-day 7 colonisation studies were done for the remaining 6,233 cases, as they had been discharged earlier.
Description by units
Of the 7,541 cases, 3,195 were in the mixed ICU and 4,346 in the Resuscitation Unit. The mixed ICU had a longer median stay (3 days) and more preventive isolation (42.3%). Common risk factors included recent hospitalisation, COPD, and antibiotics. MDRO colonisation was higher in the mixed ICU (9.9%) than in the Resuscitation Unit (5.8%). Nosocomial colonisation after 7 days was 10% in the mixed ICU and 15.5% in the Resuscitation Unit. Most discharges were to wards, with more deaths in the mixed ICU (12.6% vs. 7.1%).
Differences between initially colonised and Non-Colonised patients upon admission to ICUs
Of the 7,541 cases, 566 had initial MDRO colonisation upon ICU admission. Among them, 61% had identifiable risk factors for MDROs, while 39% did not, indicating alternative contributing factors. The median age of colonised patients was 65.9 years, compared to 63.7 years for non-colonised patients (p < 0.001). Colonised patients had a longer hospital stay (3 days vs. 2 days, p < 0.001) and higher mortality (14.5% vs. 9.0%, p < 0.001). Risk factors like prolonged hospitalisation, previous MDRO infections, and antibiotic use were more prevalent in the colonised group, with significant differences in several risk factors.
Differences between nosocomial colonised and nosocomial Non-Colonised patients
Among the 1,308 ICU patients who had colonisation controls after 7 days, 163 (12.5%) developed nosocomial MDRO colonisation. These patients had a significantly longer median hospital stay (23 vs. 13 days, p < 0.001). While 36.8% of colonised and 38.5% of non-colonised patients had risk factors, the difference was not statistically significant, suggesting other unmeasured factors may play a role.
Multivariate analysis
Multivariate logistic regression confirmed that only prolonged hospitalisation remained significantly associated with initial MDRO colonisation (OR = 1.01), reinforcing findings from the univariate analysis. Longer ICU stays increased the risk of colonisation.
Conclusion
This study examined 7,541 ICU admissions at AGUH (Spain) between April 2016 and December 2021 to understand the epidemiology and risk factors associated with MDRO (multidrug-resistant organism) colonisation. Initial colonisation was identified in 7.5% of cases, more commonly in the mixed ICU and among older male patients with chronic conditions. Significant risk factors included hospitalisation for ≥5 days in the past 3 months, known prior colonisation/infection with MDROs, and institutionalisation.
Nosocomial MDRO colonisation occurred in 12.5% of patients after 7 days in the ICU, with longer ICU stays significantly increasing the risk. While many patients with colonisation had identifiable risk factors, some did not—suggesting additional, unmeasured factors may contribute.
The findings underscore the critical need for early risk assessment, routine surveillance, targeted infection control strategies, and responsible antibiotic use in ICUs to reduce MDRO spread. Limitations include the single-centre scope, repeated admissions possibly affecting demographic data, and the pandemic’s impact on case reporting and care practices.
