Chlorhexidine vs Acinetobacter

A powerful study from Korea demonstrates the value of chlorhexidine gluconate (CHG) daily bathing of ICU patients to reduce the transmission of carbapenem-resistant Acinetobacter baumannii (CRAB). Where enhanced screening, contact precautions and environmental disinfection failed, the introduction of CHG daily bathing made an impressive reduction in the transmission of CRAB.

The study was performed in a 16 bed ICU, with a 14 month control period, and a 12 month intervention period. The authors evaluated how many patients were identified as carrying CRAB within the first 48 hours of their admission to the ICU ('prevalent' cases) and those that were first identified as carrying CRAB after 48 hours on the ICU ('incident' cases). Universal admission screening was in place throughout the study, meaning that the incident cases are presumed acquisitions. In the control period, 21% of 593 eligible admissions acquired CRAB compared with 10% of 554 admissions in the intervention period (incidence density reduced from 44 to 21 per 1000 at-risk patient days, p<0.001) (see figure below). A time series analysis confirmed a significant reduction in the incidence density of CRAB associated with the introduction of CHG.

acintobacter_graph1

Figure legend: Rate of acquisition and environmental contamination in the control and intervention periods

The authors also compared environmental contamination at one timepoint in the control period, with four timepoints in the intervention period. The proportion of sites contaminated with CRAB in the intervention period was significantly lower than in the control period (30% of 127 vs. 10% of 540) (see figure above). It is not clear whether this is due to reduced shedding of CRAB from affected cases, or due to the fact that there were less cases around due to reduced transmission; it seems likely that both contributed to the reduction in CRAB environmental contamination.

Meanwhile there was no significant change in the prevalence of CRAB on the unit, compliance with hand hygiene or contact precautions, providing firm evidence that the reduction was not due to reduced importation of CRAB into the ICU, or improvements in infection control.

Due to the potential risk for CRAB developing reduced susceptibility to CHG, the authors tested the MIC and MBC of prevalent and incident cases identified during the intervention period. (It was a shame they didn't compare cases from the control period with the intervention period - but the isolates from the control period were not saved.) They found no significant different between the MIC/MBC of prevalent and incident cases, suggesting that the daily use of CHG did not result in reduced susceptibility. It's worth noting that the median MIC/MBC was 32 mg/L, and the concentration of CHG applied to the skin was in the region of 1000x more concentrated than this, making clinically significant reduced susceptibility a distant possibility.

One of the most striking aspects of the study is the extremely high levels of CRAB on the unit. Combining prevalent and incident cases suggests that a whopping 47% of 593 eligible patients were affected by CRAB at some point during their admission. These very high levels of CRAB probably limit the generalisbility of the findings to units with a lower admission prevalence. Notwithstanding this, there was a clear step-change in the rate of CRAB acquisition associated with the introduction of CHG daily bathing, suggesting that this intervention should be performed to reduce the transmission of CRAB.

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