Decontamination: a cleaning challenge

Effective cleaning of surgical medical instruments and devices is a critical step during the decontamination reprocessing cycle. Today, decontamination is an issue of public health importance because of concerns about preventing hospital acquired infections (HAI) and minimising the risk of iatrogenic transmittable diseases. Commitment to patient safety by being able to demonstrate a verified system in which reprocessed instruments pose negligible residual contamination, and therefore reduced transmission risk, is universally accepted as an essential requirement. Iatrogenic transmission of prions (infectious proteins) poses a unique challenge to public health.1 Prions cause diseases known as transmissible spongiform encephalopathies2 (TSEs) such as Creutzfeldt-Jakob disease (CJD), variant Creutzfeldt-Jakob disease (vCJD), and Gerstmann-Sträussler-Scheinker syndrome (GSS). These diseases can be transferred through various tissues, surgical soils (proteins, fats and body fluids) and surgical device surfaces. In recent years, focus on the latter transmission route has intensified as a concerning source of prion infectivity.3 Prions and prion aggregates (amyloids) are abnormal chemical molecules belonging to a class of misfolded proteins4-6 and once a patient is infected, incubation can take a number of years without obvious physical signs. Prion diseases are currently untreatable and upon diagnosis are usually rapidly progressive and ultimately fatal.7

Assessing contamination

Assessing contamination that may remain on instruments after cleaning is usually achieved by measuring qualitatively or quantitatively the extent of protein residue. Residual protein detection is currently recommended by the Departmental of Health’s Choice Framework for local Policy and Procedures (CFPP)8 as a gauge of cleaning efficacy. The UK Government focus has been on screening every instrument for protein residues, rather than focusing on a validated method whereby all loads can be correctly processed with a high degree of confidence of attaining no protein residues. Processes which may deliver superior cleaning methods have somewhat been clouded by emphasis on residual testing. Moreover, there is a potential of misuse of protein detection as an indirect approach of addressing prion contamination. It should be noted that cleaning processes designed to be efficient at removing proteinaceous soils are at risk of being extrapolated to be effective against prion inactivation or removal. This is of concern because prions and amyloids are unusually resistant to physical decontamination9 due to their high hydrophobicity and strong affinity to metallic surfaces such as stainless steel. The choice and practicality of detecting protein residues using various methods available, including those described in CFPP, are largely dependent on the cleaning level targeted. This poses an interesting question – ‘What is the targeted cleaning level?’ We believe that this question has not yet been answered satisfactorily. Available technologies that allow accurate measurement of protein residues10,11 remaining on instruments down to nanogram (ng) quantities and beyond, require in all cases extensive and costly equipment, operational time, significant financial and staff resources. These technologies widely used in academia are at present inappropriate for routine clinical use where operational cost and turnaround are major determining factors. Furthermore, technologies that fit the need for low-cost, accurate and reliable proteinaceous residue detection do exist. These easier to use alternatives are based on the detection kit reagents strongly binding to amino acids and short peptides; the very constituents of protein residues. The affinity of these chemical reagents to protein residues is neatly demonstrated by the popular use of the Ninhydrin test,12 as recommended by CFPP. Alongside Ninhydrin, complementary detection methods such as the Biuret test and ortho-phthaldehyde (OPA) have been cited.13 The sensitivity of OPA method may be greater14 than Ninhydrin or Biuret, but continuing toxicological uncertainties related to OPA15,16 and derivative chemicals, formed upon binding to detected protein residues, give rise for cautionary use.17 This is of concern for detection methods involving actual contact of OPA with surgical instrument or devices e.g. OPA spraying on instruments, will no doubt require a repetition of washing (reprocessing) and additionally demonstrated to be chemically free prior to further surgical use.18 This, in effect, means additional time, resource and analytical testing to show instruments to be OPA free. OPA, like Ninhydrin, only binds to amino acids (alpha and epsilon amino groups13), but unlike Ninhydrin and Biuret, OPA is not a straightforward and simple visual detection test. It requires the use of sophisticated instrumentation (UV-Vis spectrophotometer or fluorometer) and equipment along with computing aids for calculating or visualising results. The use of fluorescence examinations built around the binding of OPA-protein residues is deemed expensive, resource and time dependent. Routine use of such technology is only acceptable if financial and safety concerns are met and resolved indefinitely. In short, common sense must prevail between ease of use, cost and accuracy of detection when selecting the appropriate protein residues kit. It is important to be aware that commercialised detection kits are only a useful tool towards an indicative measure of contamination. Such kits do not go far enough to determine the type of contamination, in particular potentially intact or active prions/amyloids.