Alcohol-based hand rubs (ABHR) are a pillar of infection control, recommended by the World Health Organization. The introduction of ABHR and hand hygiene to Australian hospitals from 2002 has been associated with a decrease in Staphylococcus aureus infections. However, this decrease has been paralleled by a nationwide increase in vancomycin resistant Enterococcus faecium (VRE Efm) infections. Here, we tested the hypothesis that recent clinical isolates of Efm are more tolerant than stored historical isolates to the alcohols now used extensively in hospital hand hygiene programs.
Methods: We studied 77 stored clinical isolates of Efm, 66 randomly selected by year from our hospital over 18 years (1998-2015), and 11 obtained recently from other Australian hospitals with sequence types not encountered locally. We measured log10 reduction in colony forming units after five minutes exposure to isopropyl alcohol, stratified by year of isolation and multi-locus sequence type.
Results: There was a highly significant increase in Efm alcohol tolerance over time observed across all sequence types tested in this assay, with differences of up to 4.6 log10 kill at five minutes between invasive isolates from 1998 compared to those from 2015 (log10 reduction after alcohol exposure by year of isolation; Spearman Rank r = 0.43, p < 0.0004).
Conclusions: Recent isolates of Efm obtained from bloodstream infections were significantly more tolerant to alcohol than the earliest isolates tested. The progressive gain in alcohol tolerance partly explains the failure of standard precautions that rely on alcohol-based hand rubs to control VRE cross-transmission.
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