Investigation of factors associated with mortality and vaccination effectiveness during an outbreak of Streptococcus suis disease in a swine nursery
An investigation was conducted into the potential risk factors associated with mortality during an outbreak of Streptococcus suis disease in weanling pigs. Retrospective data were used to identify both sow- and pig-level factors that could result in increased risk of mortality. A Cox’s hazard regression model identified pigs originating within certain litters that appeared to be at increased risk. Risk for individual pigs increased if a littermate died or if the pig originated from a litter where the sow’s previous litter had low mortality. During the outbreak, a proportion of litters were vaccinated using an autogenous bacterin. Direct, indirect, total, and overall measures of vaccine effectiveness were evaluated using Cox’s hazard and binomial regression models. Measures of total (~27%) and overall (~21%) vaccine effectiveness had the largest estimated magnitude, with no evidence of direct effectiveness. Overall, there is potential for benefits of vaccination despite lack of evidence of direct effectiveness.