572. Relationship Between Chlorhexidine Gluconate (CHG) Skin Concentrations and Microbial Skin Colonization among Medical Intensive Care Unit (MICU) Patients

Abstract Background CHG bathing is used to suppress patients’ microbial skin colonization, in order to prevent infections and transmission of multidrug-resistant organisms. Prior work has suggested that microbial growth is inhibited when CHG skin concentrations exceed threshold levels. Methods We conducted 6 single-day surveys from January 2018 to February 2019 in 7 academic hospital MICUs with established CHG patient bathing. Adult patients were eligible to have skin swabbed from adjacent 25 cm2 areas on the neck, axilla, and inguinal region for culture and CHG concentration determination. CHG skin concentrations were measured by a semi-quantitative colorimetric assay. Selective media were used to isolate targeted microorganisms (Table 1). Species were confirmed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry; antibiotic susceptibility was determined by MicroScan (Beckman Coulter). We modeled the relationship between CHG skin concentrations (log2-transformed) and microorganism recovery (yes/no as primary outcome) using multilevel models controlling for clustering of body sites within patients and within ICUs, assessing slope and threshold effects. Results We enrolled 736/759 (97%) patients and sampled 2176 skin sites. Gram-positive bacteria were detected most frequently (Table 1). The adjusted odds of identifying gram-positive organisms decreased linearly as CHG skin levels increased (Figure 1a), without evidence of a threshold effect. We also found significant negative linear slopes without evidence of threshold effects for other pathogens tested (Table 2; Figure 1), with the exception of gram-negative bacteria and vancomycin-resistant enterococci. When modeling quantitative culture results (colony-forming units) for gram-positive organisms as a continuous outcome variable, a similar relationship was found. Conclusion Higher concentrations of CHG were associated with less frequent recovery of gram-positive bacteria and Candida species on the skin of MICU patients who were bathed routinely with CHG. For microbial inhibition, we did not identify a threshold concentration of CHG on the skin; rather, increasing CHG skin concentrations led to additional gains in inhibition. For infection prevention, aiming for high CHG skin levels may be beneficial. Disclosures All authors: No reported disclosures.