At present both the prevalence of subclinical vCJD and its degree of infectivity via surgical instruments are unknown. Also, no cases of iatrogenic vCJD in humans have so far been identified. Nevertheless, based on the evidence we do have, we can make judgments about the features that are likely to affect the size of the risk from surgical instruments.

So far the disease marker (and likely transmissible agent) for vCJD (PrP^Sc) has been identified by sensitive western blot techniques in the neural and lymphoreticular tissues of brain, tonsil, and spleen.² A positive appendix (which consists largely of lymphoreticular tissue) has not yet been reported using this technique, though one archived appendix has been reported to be positive using immunohistochemical staining.³

There is clear evidence from case reports in humans and animal models that prion diseases can be transmitted via stainless steel instruments.^4,5 Also the infective agent of iatrogenic prion diseases has shown remarkable resistance to the conventional sterilisation techniques used for surgical instruments.⁶ The incubation period of vCJD is unknown but could be several decades,⁷ so it is therefore unlikely that any iatrogenic cases will have yet emerged. The precautionary principle suggests that when the potential risk to public health is substantial there is no case for sitting back to wait for indisputable evidence. This view has influenced the British government's previous decision to leucodeplete all blood and blood products.⁸

So what is the purpose of the new policy to upgrade decontamination facilities?

The most effective generic approach to preventing vCJD transmission is thought to be to remove all traces of organic material at the washing phase of the decontamination process (washing, disinfection, and sterilisation).⁶ Some decontamination facilities in British hospitals are relatively old, and upgrading them should enable more effective decontamination. This should reduce the risk of transmission of vCJD and of other (including unknown) diseases. Measures are also being introduced to enable all reusable surgical instrument sets to be traced.⁹

Why won't these general measures do for adenotonsillectomy and why must this procedure, specifically, be performed with disposable instruments? We know through animal models that PrP^Sc becomes positive in lymphoreticular tissues relatively early in the incubation period.¹⁰ The population undergoing adenotonsillectomy is young (median age 9 years) and has a further life expectancy of about 65 years. Even if vCJD has an incubation period of several decades, the potential impact of iatrogenic transmission to children is particularly serious. Tonsillectomy and adenoidectomy are common operations (about 69000 were performed in the UK in 1999-2001¹¹). The instrument sets are reused often, and their time in service often exceeds 10 years. Therefore, each set of instruments will over its lifetime have come into contact with many patients, significantly increasing the risk of contamination. In this situation, even if the relative risk is low, the population attributable risk is probably high. This attributable risk reflects the potential numbers of patients who could be affected. If the prevalence of preclinical disease is, say, 1 in 10000, then about 30% of ear, nose, and throat units could have a contaminated instrument set in the operating theatre.¹² This risk is likely to be increased as instruments tend to “wander” across to other instrument sets with time.

By contrast, patients undergoing lymph node excisions and neurosurgery are usually older and have generally shorter life expectancies. PrP^Sc is expressed in neural tissue relatively late in the incubation period, and neurosurgical operations are performed on fewer patients. Compared with the population undergoing adenotonsillectomy, these patients are likely to have a lower attributable risk.

The case for disposable instruments in appendicectomy remains less clear. So far, the evidence that the appendix is a reliable site for abnormal prion expression is weaker than for tonsils, with only a single case reported with positive immunohistochemistry. However, this operation shares many of the risk attributes of tonsillectomy in that the patient population is otherwise healthy and young and the operation is common.