Assessment of spatial and temporal clustering of ampicillin- and tetracycline-resistant strains of Pasteurella multocida and P haemolytica isolated from cattle in California
Singer, R.S.; Case, J.T.; Carpenter, T.E.; Walker, R.L.; Hirsh, D.C.
Journal of the American Veterinary Medical Association 212(7): 1001-1005
1998
ISSN/ISBN: 0003-1488 PMID: 9540872 Document Number: 492716
Records of the California Veterinary Diagnostic Laboratory System were reviewed, and information was obtained on P. multocida and P. haemolytica isolates obtained from lung or tracheal wash samples collected from cattle with pneumonia and submitted for bacterial culture between July 1991 and July 1996. Spatial clustering of ampicillin- and tetracycline-resistant isolates was assessed by use of nearest-neighbour 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. Data were obtained for 219 P. multocida and 127 P. haemolytica isolates. 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. The 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.