Factors determining the potential for onward transmission of variant Creutzfeldt-Jakob disease via surgical instruments

Abstract

While the number of variant Creutzfeldt-Jakob disease (vCJD) cases continues to decline, concern has been raised that transmission could occur directly from one person to another through routes including the transfer of blood and shared use of surgical instruments. Here we firstly present data on the surgical procedures undertaken on vCJD patients prior to onset of clinical symptoms, which supports the hypothesis that cases via this route are possible. We then apply a mathematical framework to assess the potential for self-sustaining epidemics via surgical procedures. Data from hospital episode statistics on the rates of high- and medium-risk procedures in the UK were used to estimate model parameters, and sensitivity to other unknown parameters about surgically transmitted vCJD was assessed. Our results demonstrate that a key uncertainty determining the scale of an epidemic and whether it is self-sustaining is the number of times a single instrument is re-used, alongside the infectivity of contaminated instruments and the effectiveness of cleaning. A survey into the frequency of re-use of surgical instruments would help reduce these uncertainties.

Figure 1

The number of operations performed prior to the onset of clinical symptoms on 130 vCJD cases. (a) By the number of years prior to onset of clinical symptoms in the case; (b) frequency of multiple operations.

Figure 2

Age-distribution of the annual number of operations performed in England stratified by the high- and medium-risk classification.

Figure 3

Flowchart of cohort c of the population: susceptibles X_c and primary/secondary infected $Y_c^{(1/2)}$. During the first part of the incubation period, pre- as well as sub-clinical individuals are non-infectious, in the later stages of incubation, they are infectious. D^(1/2) are the cumulative deaths from primary/secondary infection.

Figure 4

The figure shows how the basic reproductive number R₀ given in equation (4.13) depends on the combined transmission parameter, β_ihβ_hi and the average number of procedures an instrument is used in before it is discarded, d. (a) For high-risk procedures and (b) for medium-risk procedures. For this figure we assume that pre- and sub-clinically infected individuals are infectious throughout their incubation period and that 40% of secondary infections are sub-clinical.

Figure 5

Basic reproductive number R₀ dependent on the probability of sub-clinical infection ω₂ and the infectious proportion of the incubation period ρ_pre for high-risk operations. Parameter values used were the combined transmission parameter β_ihβ_hi=1, the average number of re-uses per instrument d=1 and the rate of progression through the incubation stages γ₂=0.877 per year.

Figure 6

Predicted number of deaths from secondary infection between 2006 and 2021, dependent on the basic reproductive number R₀ and the probability of sub-clinical infection ω₂ for high-risk procedures (a and b) and medium-risk procedures (c and d).

Figure 7

Probability of survival dependent on age.