Is there the potential for an epidemic of variant Creutzfeldt-Jakob disease via blood transfusion in the UK?

Abstract

The discovery of three individuals suspected to have contracted variant Creutzfeldt-Jakob disease (vCJD) through blood transfusions has heightened concerns that a secondary epidemic via human-to-human transmission could occur in the UK. The Department of Health responded immediately to this threat by banning those who had received blood transfusions since 1980 from donating blood. In this paper, we conduct a sensitivity analysis to explore the potential size of a blood-borne vCJD epidemic and investigate the effectiveness of public health interventions. A mathematical model was developed together with an expression for the basic reproduction number (R0). The sensitivity of model predictions to unknown parameters determining the transmission of vCJD via infected blood was assessed under pessimistic modelling assumptions. We found that the size of the epidemic (up until 2080) was bounded above by 900 cases, with self-sustaining epidemics (R0>1) also possible; but the scenarios under which such epidemics could arise were found to be biologically implausible. Under optimistic assumptions, public health interventions reduced the upper bound to 250 and further still when only biologically plausible scenarios were considered. Our results support the belief that scenarios leading to large or self-sustaining epidemics are possible but unlikely, and that public health interventions were effective.

Figure 1

Data on blood supply and UK mortality rates. (a) Whole blood donation rates by age obtained from national figures provided by the NBS in 1997. (b) Red cell transfusion rates by age group obtained from a 28-day prospective observational study in the North of England (Wells et al. 2002). The destination of 9848 units (97% of expected blood use) was recorded. (c) The overall survival probability for the UK obtained from 1993 census data (Ghani et al. 1998). (d) 2- and 5-year survival probabilities by age group for patients receiving red cell transfusions from the prospective observational study in the North of England (Wallis et al. 2004). Corresponding estimates of the 2- and 5-year post surgery survival probabilities used in the mathematical model are also shown.

Figure 2

Sensitivity analysis. The relationship between R₀, epidemiological parameters and future infections and clinical cases without interventions. (a) R₀ and the transmission probability from blood. (b) R₀ and the ratio of the mean incubation period in those infected via blood transfusion to the mean incubation period in those infected via consumption of BSE-infected beef. (c) The total number of clinical cases by 2080 and the ratio of the mean incubation periods for those infected via blood transfusion and those infected via consumption of BSE-infected beef clinical cases by 2080. (d) The total number of clinical cases by 2080 and the probability of entering a carrier state after infection via blood transfusion. (e) The total number of people infected via blood transfusion by 2080 and the mean incubation period ratio. (f) The total number of infections by 2080 and the carrier state probability for blood-borne infections.

Figure 3

A sample epidemic. Two scenario epidemics. (a) An epidemic with low R₀=0.03 showing that the vast majority of vCJD clinical cases arise via primary infection. (b) An epidemic with high R₀=1.3 showing a multi-modal distribution of vCJD cases with the first peak occurring in 2000 from primary transmission and a second, much lower, peak in 2060 from transfusion-acquired infection. In both the scenarios, it is assumed that 10% of those infected via blood transfusion go on to develop clinical disease and that no interventions have taken place.