The Principles of Medical Device Decontamination

What causes an immunocompromised state?

The immune system 12 is responsible for “policing” the body, recognising, removing and destroying foreign substances and cells, including cancer cells and infecting microorganisms. Immune defences however are broader than the cells of the immune system and effector substances they produce. The skin and intact mucous membranes are the first line of defence. Breaches of normal defences include insertion of peripheral or central venous catheters, urinary catheters, endotracheal tubes, medical devices: pacing wires, heart valves, implanted joints, urinary and biliary stents, arterial stents etc. As well as breaching normal defences, medical devices can allow for the deposition of a biofilm over time, which can include bacteria and therefore be a constant source of ongoing potential infection. Most patients in secondary care will be immunocompromised to a greater or lesser extent because of the procedures, medical devices and drugs used to support them, as indicated in the preceding paragraph. The more healthcare interventions used with a patient to manage an illness, the more immunocompromised they can become and the greater their susceptibility to infection. The risk of healthcare associated infection in a cancer patient already on immunosuppressive treatment who has just undergone major cancer surgery, including the use of prophylactic antibiotics will be at considerable risk of infection with antibiotic resistant bacteria.

Biofilms

Biofilms are important in healthcare 13 but also to the decontamination processes. A biofilm is a complex mix of protein, cellular deposits, and bacteria, tightly bound to a surface. In healthcare, biofilms can be associated both spontaneously in tissue and with indwelling medical devices. Some chronic wounds will develop a biofilm and to achieve wound healing it will be necessary to remove the biofilm. Similarly, a vegetation on a heart valve associated with endocarditis is a type of biofilm. Getting antibiotics into these complex biofilms is very difficult because by their very nature, they do not have a blood supply, which is why simply prescribing an antibiotic for a chronic wound has little effect other than to select for multi-drug resistant organisms. Endocarditis requires very high doses of antibiotics to set up a diffusion

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