title: Assessment of spatial and temporal clustering of ampicillin- and tetracycline-resistant strains of Pasteurella multocida and P haemolytica isolated from cattle in California.
abstract: OBJECTIVE
  To determine whether ampicillin- and tetracycline-resistant strains of Pasteurella multocida and P haemolytica isolated from California cattle with pneumonia were spatially and temporally clustered and to compare overall estimates of percentages of these isolates resistant to these antimicrobials with estimates obtained on the basis of regional and temporal information.
  
  
  METHODS
  Epidemiologic study.
  
  
  METHODS
  Records of P multocida and P haemolytica isolates obtained from lung or tracheal wash samples collected from California cattle with pneumonia between July 1, 1991 and July 31, 1996. Only isolates obtained from samples submitted by dairies and calf ranches were used.
  
  
  METHODS
  Spatial clustering of ampicillin- and tetracycline-resistant isolates was assessed by use of nearest-neighbor and Cuzick and Edwards' analyses. Linear clustering along a north-south line was assessed by use of runs and maximum length of runs tests. Temporal clustering was assessed by use of scan tests. Spatial-temporal clustering was assessed by use of Barton's method. Regional estimates of percentages of P multocida and P haemolytica resistant to ampicillin or tetracycline were calculated.
  
  
  RESULTS
  There was significant spatial clustering of resistant isolates and significant linear clustering along a north-south line. Significant differences in regional estimates of percentages of antimicrobial-resistant isolates were found.
  
  
  CONCLUSIONS
  Results support the hypothesis that antimicrobial-resistant organisms can be clustered at the local level and reinforce the need to establish regional estimates of percentages of bacterial isolates that will be susceptible to commonly used antimicrobials.
authors.affiliation: Department of Pathology, Microbiology, and Immunology, School of Veterinary Medicine, University of California, Davis 95616-8734, USA.
authors.forename: R S
authors.initials: RS
authors.lastname: Singer
authors.forename: J T
authors.initials: JT
authors.lastname: Case
authors.forename: T E
authors.initials: TE
authors.lastname: Carpenter
authors.forename: R L
authors.initials: RL
authors.lastname: Walker
authors.forename: D C
authors.initials: DC
authors.lastname: Hirsh
mesh_terms: D000668:Ampicillin Resistance; D000818:Animals; D002140:California / Q000453:epidemiology; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology / Q000382:microbiology*; D008168:Lung / Q000382:microbiology; D016978:Mannheimia haemolytica / Q000187:drug effects* / Q000302:isolation & purification; D010326:Pasteurella Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D016979:Pasteurella multocida / Q000187:drug effects* / Q000302:isolation & purification; D018410:Pneumonia, Bacterial / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D013029:Space-Time Clustering; D013753:Tetracycline Resistance; D014132:Trachea / Q000382:microbiology