title: Air sampling in the breathing zone of neonatal foals for prediction of subclinical Rhodococcus equi infection.
abstract: BACKGROUND
  Disease caused by Rhodococcus equi is a significant burden to the horse breeding industry worldwide. Early detection of rhodococcal pneumonia, albeit important to minimise treatment costs, is difficult because of the insidious nature of the disease and the lack of definitive diagnostic tests.
  
  
  OBJECTIVE
  To investigate air sampling from the breathing zone of neonatal foals as a predictor of subsequent rhodococcal pneumonia.
  
  
  METHODS
  Air samples were collected from the breathing zone of 53 neonatal foals (age ≤10 days) and again at the time of routine ultrasonographic screening for R. equi pneumonia (age 1-2 months).
  
  
  RESULTS
  Pneumonia was diagnosed ultrasonographically in 23% of foals. Virulent R. equi was detected in air from the breathing zone of 19% of neonatal foals and 45% of foals at age 1-2 months. There was no association between virulent R. equi in the breathing zone of foals and the subsequent ultrasonographic diagnosis of rhodococcal pneumonia. The median concentration of virulent R. equi in the breathing zone of both neonates (0 [range 0-4] colony-forming units [cfu]/250 l) and older foals (0 [range 0-3] cfu/250 l) was not significantly different from that in background air samples (0 [range 0-6] cfu/250 l). There was no difference in the concentration of virulent R. equi in the breathing zone of older foals that were diagnosed with rhodococcal pneumonia or clinically normal foals.
  
  
  CONCLUSIONS
  Detection of virulent R. equi in air from the breathing zone was not a positive predictor of rhodococcal pneumonia in foals up to age ≤2 months.
  
  
  CONCLUSIONS
  Selective culture of air samples from the breathing zone of young foals is not better at diagnosing rhodococcal pneumonia than early ultrasonographic screening. However, culture of air samples from the breathing zone of older foals remains a useful herd-based epidemiological tool.
authors.affiliation: Equine Infectious Disease Laboratory, Veterinary Pre-Clinical Centre, The University of Melbourne, Victoria, Australia.
authors.forename: C
authors.initials: C
authors.lastname: Chicken
authors.forename: G
authors.initials: G
authors.lastname: Muscatello
authors.forename: J
authors.initials: J
authors.lastname: Freestone
authors.forename: G A
authors.initials: GA
authors.lastname: Anderson
authors.forename: G F
authors.initials: GF
authors.lastname: Browning
authors.forename: J R
authors.initials: JR
authors.lastname: Gilkerson
mesh_terms: D000193:Actinomycetales Infections / Q000209:etiology / Q000662:veterinary*; D000391:Air Microbiology; D000818:Animals; D000831:Animals, Newborn; D006734:Horse Diseases / Q000382:microbiology*; D006736:Horses; D018410:Pneumonia, Bacterial / Q000382:microbiology / Q000662:veterinary; D016929:Rhodococcus equi / Q000302:isolation & purification* / Q000472:pathogenicity; D014774:Virulence