Risk factors for intensive care unit acquired nasal colonization of MRSA and its impact on MRSA infection

Phenotype-Genotype Characterization and Antibiotic-Resistance Correlations Among Colonizing and Infectious Methicillin-Resistant Staphylococcus aureus Recovered from Intensive Care Units

Introduction

Methicillin-resistant Staphylococcus aureus (MRSA) presents a profound hazard to public health. MRSA colonizing skin, mucous membranes, and the anterior nares without clinical symptoms is termed "colonizing MRSA". Upon manifestation of clinical symptoms, it is termed "infectious MRSA". Here, we characterize and differentiate colonizing and infectious MRSA, and analyze the phenotypic-genotypic and antibiotic susceptibility correlations.

Methodology

Clinical MRSA isolates were recovered from intensive care units (ICUs) of two major Egyptian hospitals and their biofilm formation ability was tested. Antibiograms against 16 antibiotics were determined, in addition to the minimum inhibitory concentrations (MICs) of vancomycin and linezolid. The entire collection was typed by enterobacterial repetitive intergenic consensus (ERIC)-PCR, as well as multi-locus sequence typing (MLST). Representative resistance and virulence genes were detected by PCR amplification.

Results

Forty-nine isolates were confirmed as MRSA, of which 30 isolates were infectious and 19 were colonizing. Versatile resistance patterns were observed in both groups of isolates. We report a higher tendency for biofilm-formation and borderline minimum inhibitory concentrations among infectious isolates. A Positive antibiotic correlation was observed between susceptibility to protein synthesis inhibitors and cell wall inhibitors. Positive correlations were observed between isolation site and rifampicin resistance: nasal samples were enriched in rifampicin-resistant isolates, while urine and blood samples were enriched in susceptible ones. Furthermore, biofilm formation ability was slightly associated with amikacin resistance, and an association between teicoplanin resistance and the presence of the Panton-Valentine leukocidin gene was the only significant phenotype-genotype correlation observed. Finally, ERIC typing and MLST had congruent results.

Conclusion

Linezolid and vancomycin are still the most convenient choice for MRSA treatment. ERIC PCR and MLST show promising typing combination that could be easily used periodically for tracking the genotypic changes of MRSA, especially within the healthcare facilities. Several correlations were established between groups of antibiotics and the genotypes/phenotypes of the selected isolates.

Interplay of nasal and rectal carriage of Staphylococcus aureus in intensive care unit patients

The aim of this study was to investigate the relationship between nasal and rectal Staphylococcus aureus carriage in intensive care unit (ICU) patients and the occurrence of ICU-acquired infections related to S. aureus carriage. Three hundred and ninety-five patients admitted in ICU were screened for S. aureus nasal and rectal carriages and followed to record S. aureus infections during their stay. S. aureus strains were genotyped by arbitrarily primed PCR, spa-typing, microarray and whole genome sequencing. At ICU admission, 112 of 363 (30.9%) patients carried S. aureus including 61 (16.8%) exclusive nasal carriers, 40 (11.0%) combined nasal and rectal carriers and 11 (3.0%) exclusive rectal carriers. The 152 S. aureus isolates from nasal and rectal swabs belonged to 19 clonal complexes (CCs). Patients colonized in both nose and rectum harboured different strains in at least 40% of cases according to arbitrarily primed PCR data. Nasal carriers of CC5 S. aureus had an increased risk of rectal carriage (RR = 1.85, P < .05). S. aureus nasal and rectal carriage was a risk factor of S. aureus ICU-acquired infection (RR = 4.04; 95%CI [1.38-11.76]). Incidence rates of endogenous ICU-acquired infections in exclusive nasal carriers, exclusive rectal carriers and in both nasal and rectal carriers were 0.08 (5/61), 0.09 (1/11) and 0.03 (1/40), respectively (p = 0.47). Rectal swabbing increased the detection of S. aureus carriage and revealed an important diversity of S. aureus strains in ICU patients. Further studies are needed to understand how S. aureus rectal carriage increases the risk of endogenous ICU-acquired infections.

Methicillin-Resistant Staphylococcus aureus and Other Multidrug-Resistant Colonizations/Infections in an Intensive Care Unit: Predictive Factors

INTRODUCTION AND OBJECTIVES

Methicillin-resistant Staphylococcus aureus (MRSA) is the most prevalent pathogen causing nosocomial infections in hospitals and health centers. This work is an effort to understand the epidemiology of MRSA and other multidrug-resistant pathogens in an intensive care unit (ICU) and to analyze characteristics that might determine the risk of MRSA colonization/infection in this unit.

METHOD

An observational, 1-year prospective longitudinal study was conducted to obtain information about MRSA and other multidrug-resistant colonizations/infections. The study was conducted with ICU patients with an artificial airway. Data were obtained from the National Study of the Control of Nosocomial Infections in Intensive Care Units database.

RESULTS

MRSA colonization was highly prevalent (33%); however, other pathogens like gram(-) Bacillus showed a higher infectious potency. Acute Physiology and Chronic Health Evaluation (APACHE-II) score >15 and hospital stay of >4 days were the main variables that significantly predicted the risk of developing MRSA colonization ( p < .001 in both cases). Moreover, the presence of MRSA increased the risk of developing a second multidrug-resistant colonization/infection, especially with methicillin-resistant Pseudomona.

DISCUSSION

The high prevalence of MRSA emphasizes the need to continue studying risk factors for MRSA colonization/infection, which may allow early identification of this pathogen. Therefore, we propose the use of the APACHE-II score and length of hospital stay to predict increased risk of MRSA colonization. Awareness of the heightened risk in particular patients could lead to early detection and prevention.