Management and demographic factors associated with seropositivity to transmissible gastroenteritis virus in US swine herds, 1989–1990

Serum neutralization testing was used to determine transmissible gastroenteritis (TGE) titers of up to 10 sows per herd (mean 8.7, median 10) for 392 herds that participated in the 3 month monitoring of sows and litters in the National Swine Survey. Of the sampled herds, 101 (25.8%) had sow seroprevalences of at least 80%, 79 (20.1%) had seroprevalences between 10 and 79%, and 212 (54.1%) were seronegative. For evaluation of risk factors for TGE seropositivity, analysis was restricted to herds with at least five tested sows and either 0% or at least 20% seropositive sows. In the logistic regression analysis, a herd was considered seropositive if at least 20% of sampled females had titers of 1: 8 or higher (n = 160), and a herd was seronegative if all females had titers of under 1: 8 (n = 178). Factors considered for inclusion in logistic regression models included breeding herd size, biosecurity measures, pig introductions and movements, and access of possible nonporcine reservoirs to the facilities with pigs. After controlling for the effects of season, number of samples tested and TGE vaccination history, large female breeding herd size (at least 500 sows compared with the reference category of 100–199 sows) and purchase of more than 25 pigs from non-specific pathogen free (SPF) herds were associated with significantly (P<0.05) higher odds of herd seropositivity (odds ratios 4.9 and 3.9, respectively). There was some evidence (P = 0.08) of an increased risk of seropositivity when there were more than two swine herds within a 3 mile radius of the study herd.