UK dietary exposure to BSE in beef mechanically recovered meat: by birth cohort and gender.

Abstract

Background: Meat recovered mechanically from bovine vertebral columns for use in burgers, sausages and other meat products may have been contaminated with bovine spongiform encephalopathy (BSE) from recovered spinal cord and dorsal root ganglia (DRG). We quantified UK exposure to BSE in beef mechanically recovered meat (MRM) by birth cohort (born pre-1940, in 1940-1969, post-1969), gender and calendar period (1980-1989, 1990-1996) because information on any two of BSE exposure intensity, vCJD incubation period and the new cases of vCJD tells us about the third.

Methods: Synthesis of evidence on BSE epidemiology, MRM production, infectivity in spinal cord and DRG, and UK dietary consumption.

Findings: Production of beef MRM peaked at 5000 tonnes in 1987, was nil in 1989 but recovered to 2000 tonnes in 1995 when it ceased altogether; reportedly 90% was used in burgers. Mean weight of spinal cord recovered per carcass was 3.3 g (95% credible interval 0.24-12.02 g) before the specified bovine offal (SBO) legislation and 1.5 g (0.02-8.30 g) after the legislation; whereas recovered weight of DRG (as infectious as spinal cord) was 27 g. Recovery of spinal cord from 1-year pre-clinical bovines peaked in 1988 at 238 g and of DRG in 1993 at 4250 g (medians). Median infectivity (5th and 95th percentiles) consumed in beef MRM was 33 250 (30 550-35 950), 65 600 (60 250-71 050) and 14 350 (13 150-15 600) bovine oral (Bo) ID50 units for the post-1969, 1940-1969 and pre-1940 birth cohorts in 1980-1989; and 44 250 (41 300-47 350), 39 600 (37 100-42,400) and 8750 (8100-9350) Bo ID50 units in 1990-1996. Males consumed almost 58% of infectivity in both periods. If the worst-case level of infectivity pertained, exposure, instead of halving in 1990-1996, would be sustained at around its 1980-1989 level for the two older birth cohorts and would have doubled in 1990-1996 for the post-1969 birth cohort.

Interpretation: SBO legislation in 1989 contributed only a 6% reduction in the infectivity in beef MRM. Salient sensitivity issues are highlighted.