Estimation of the basic reproduction ratio (R₀) for Shiga toxin-producing Escherichia coli O157:H7 (STEC O157) in beef calves

To understand the dynamics of transmission of Shiga toxin-producing Escherichia coli O157:H7 (STEC O157) in beef calves, serum samples were obtained from calves in a beef cow-calf herd approximately every 6 weeks from birth until weaning for three consecutive years. The presence of specific anti-O157 antibodies in these serum samples was detected using a blocking ELISA assay incorporating an anti-O157 monoclonal antibody. Using seroconversion data, the basic reproduction ratio (R₀) was estimated for each of the three years as well as in aggregate using both deterministic and Martingale methods. R₀ for STEC O157 infection in range beef calves by deterministic methods varied from 2.9-5.6, with an average of 4.3 (95% CI 2.8-5.9). Martingale estimates of R₀ ranged from 3.5-7.4, or 5.3 (95% CI 3.9-6.6), for data from all three years. Given the above estimate of R₀, it is predicted that 65-86% of a herd of calves must be effectively vaccinated, or must be rendered non-susceptible through other means, to eliminate STEC O157 infection from a herd.