Application and evaluation of a mailed questionnaire for an epidemiologic study of Corynebacterium pseudotuberculosis infection in horses

A 6-page questionnaire was designed to collect information from owners of 134 horses diagnosed with C. pseudotuberculosis infection at the UC Davis Veterinary Medical Teaching Hospital (VMTH) between 1 July 1992 and 30 June 1994 and a further 800 control horses, to evaluate risk factors. The questionnaire was mailed to the owners, followed by a reminder postcard and a second copy of the questionnaire. Data were collected on owner and horse identity, demographics, horse management and use, geographic location, and general health-related issues. 44 horses were excluded from part of the study. The overall return proportion was 66% (587/890), and the completion proportion 55% (491/890). The number of returns over time followed a negative binomial distribution, with over 90% of all returns being in by the end of the fifth week after mailing, and over 99% at the end of the tenth week. Some categories within the variables age (between 2 and 3 years), breed (Thoroughbred and Standardbred horses) and gender (stallions) had significantly lower return proportions than expected (differential return). The profile of these horses fits a section of the racehorse population that is served by the VMTH. There was good agreement between data from existing medical records and the questionnaires, and it is concluded that the quality of the survey information was sufficient to perform a risk-factor analysis. The mailed survey provided a rapid and cost-effective method of collecting additional information to supplement existing medical records.