Association of airborne concentration of virulent Rhodococcus equi with location (stall versus paddock) and month (January through June) on 30 horse breeding farms in central Kentucky

Association of airborne concentration of virulent Rhodococcus equi with location (stall versus paddock) and month (January through June) on 30 horse breeding farms in central Kentucky

2012

Objective: To determine whether the concentration of airborne virulent Rhodococcus equi varied by location (stall vs paddock) and month on horse farms. Sample: Air samples from stalls and paddocks used to house mares and foals on 30 horse breeding farms in central Kentucky. Procedures: Air samples from 1 stall and 1 paddock were obtained monthly from each farm from January through June 2009. Concentrations of airborne virulent R equi were determined via a modified colony immunoblot assay. Random-effects logistic regression was used to determine the association of the presence of airborne virulent R equi with location from which air samples were obtained and month during which samples were collected. Results: Of 180 air samples, virulent R equi was identified in 49 (27%) and 13 (7%) obtained from stalls and paddocks, respectively. The OR of detecting virulent R equi in air samples from stalls versus paddocks was 5.2 (95% confidence interval, 2.1 to 13.1). Of 60 air samples, virulent R equi was identified in 25 (42%), 18 (30%), and 6 (10%) obtained from stalls during January and February, March and April, and May and June, respectively. The OR of detecting virulent R equi from stall air samples collected during May and June versus January and February was 0.22 (95% confidence interval, 0.08 to 0.63). Conclusions and Clinical Relevance: Foals were more likely to be exposed to airborne virulent R equi when housed in stalls versus paddocks and earlier (January and February) versus later (May and June) during the foaling season.

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