False positive results of Bowie and Dick type test used for hospital steam sterilizer with slower come-up ramps: A case study

ObjectiveTo determine if the standardized B&D type test for hospital steam sterilizer is correctly indicating cycle failures in slower come-up ramps cycles.MethodsTwo commercially available B&D type test were challenged in a quality control sterilizer. A common failure was simulated in triplicate cycles, using a standardized cycle configuration, and then compared to triplicate cycles of a common cycle configuration. Tests procedures were conducted according to B&D manufacturer test standard and results were compared to standardized endpoint specifications.ResultsWe found that B&D type tests are only capable of detecting the presence of non-condensable gases if the sterilization equipment is adjusted to meet all the cycle requirements of the test. False positive results were obtained with come-up ramp time of 3 min. Correct results were only obtained with come-up ramp of 1.7–1.9 min.ConclusionsUntil the ISO 17665 and AAMI ST-79 standards are revised, equipment qualification experts should observe come-up time duration criterion for B&D type test cycles according to ISO 11140–4. Sterile Processing Department professionals must add the come-up ramp criterion to cycle evaluation before clearing the equipment for routine use. This will allow B&D correct performance, reducing the infection risk from unsterilized medical device.研究目的：明确医用蒸汽灭菌器（hospital steam sterilizer）的标准化B&D型试验（B&D type test）在升温斜坡循环中能否正确指示循环故障。研究方法：选取两款市售B&D型试验装置，在一台质控用蒸汽灭菌器中开展挑战试验。采用标准化循环配置，对1种典型故障开展三次重复循环模拟，并与采用通用循环配置的三次重复循环试验进行对比。试验流程严格遵循B&D厂商的试验标准，并将试验结果与标准化终点规格进行比对。研究结果：研究发现，仅当灭菌设备调试至满足该试验的全部循环要求时，B&D型试验才能检出不凝性气体（non-condensable gases）的存在。当升温斜坡时长为3分钟时，会出现假阳性结果；仅当升温斜坡时长处于1.7~1.9分钟区间时，方可获得准确试验结果。研究结论：在ISO 17665与AAMI ST-79标准修订之前，设备资质认定专家应依据ISO 11140–4的要求，严格遵守B&D型试验循环的升温时长判定准则。消毒供应中心（Sterile Processing Department）从业人员必须在将设备放行用于常规使用前，将升温斜坡判定准则纳入循环评估流程。此举可保障B&D型试验的准确执行，降低未灭菌医疗器械引发的感染风险。