ATP measurements in the last rinse water of automated washer-disinfectors: the added value of every load monitoring

Objective: To assess whether monitoring every loads of automated washer-disinfectors (AWDs) by testing the last rinse water with Adenosine Triphosphate (ATP) would have an added value to document effective and reproducible AWD processes. Methods: Every load monitoring (ELM) of the last rinse water with ATP was performed on three AWDs at the sterilization department of a 329 acute-bed hospital in Italy. No change were made in the routine procedures, except the last rinse water of a process was collected with a water sampler and tested on ATP. Data from negative controls and empty cycles were also obtained for comparison. ATP values were analysed according to AWD, load, and process characteristics. Results: A total of 435 ATP tests were performed, including 74 negative, 74 empty runs and 287 regular load tests. ATP values from regular loads ranged between 2 and 452 RLUs and 1.3%, 0.7%, 0.3% out of the 287 measurements was above 200, 300, and 400 RLUs, respectively. ATP values from negative tests and empty runs differed significantly (p<0.001) from the regular loads with a median value [I quartile; III quartile] of 4[2;5], 5[3;7], and 12[7;22] RLU, respectively. Analysis of ATP values from regular loads grouped by load pre-treatment, AWD washing program, load material or load amount showed significant differences between groups. No significant differences in ATP data were found among AWDs. Conclusion: The measurement of ATP in the last rinse water of AWDs showed that characteristics and quantities of the load relate to the ATP readings. The test is advised as an informative additional test to visual inspection for monitoring every load of an AWD.