ASSESSMENT OF SPATIAL AND TEMPORAL CLUSTERING OF AMPICILLIN-RESISTANTAND TETRACYCLINE-RESISTANT STRAINS OF PASTEURELLA-MULTOCIDA AND P-HAEMOLYTICA ISOLATED FROM CATTLE IN CALIFORNIA

Objective-To determine whether ampicillin-and tetracycline-resistant s trains of Pasteurella multocida and P haemolytica isolated from Califo rnia cattle with pneumonia were spatially and temporally clustered and to compare overall estimates of percentages of these isolates resista nt to these antimicrobials with estimates obtained on the basis of reg ional and temporal information. Design-Epidemiologic study. Sample Pop ulation-Records of P multocida and P haemolytica isolates obtained fro m lung or tracheal wash samples collected from California cattle with pneumonia between July 1, 1991 and July 31, 1996. Only isolates obtain ed from samples submitted by dairies and calf ranches were used. Proce dure-Spatial clustering of ampicillin- and tetracycline-resistant isol ates was assessed by use of nearest-neighbor and Cuzick and Edwards' a nalyses. linear clustering along a north-south line was assessed by us e of runs and maximum length of runs tests. Temporal clustering was as sessed by use of scan tests. Spatial-temporal clustering was assessed by use of Barton's method. Regional estimates oi percentages of P mult ocida and P haemolytica resistant to ampicillin or tetracycline were c alculated. Results-There was significant spatial clustering of resista nt isolates and significant linear clustering along a north-south line . Significant differences in regional estimates of percentages of anti microbial-resistant isolates were found. Clinical Implications-Results support the hypothesis that antimicrobial-resistant organisms can be clustered at the local level and reinforce the need to establish regio nal estimates of percentages of bacterial isolates that will be suscep tible to commonly used antimicrobials.