STREPTOCOCCUS-SUIS INFECTION IN SWINE - A RETROSPECTIVE STUDY OF 256 CASES .1. EPIDEMIOLOGIC FACTORS AND ANTIBIOTIC SUSCEPTIBILITY PATTERNS

A retrospective study of 256 cases of naturally acquired Streptococcus suis infections in swine submitted to the Indiana Animal Disease Diag nostic Laboratory from 1985 to 1989 was performed to determine the epi demiologic factors and antibiotic susceptibility patterns associated w ith S. suis serotypes 1-8 and 1/2. A standardized computer form was us ed to record the history, signalment, and clinical signs obtained from the records of selected cases and the microscopic lesions identified after review of the histopathology slides for each case. A computer st atistics package (SAS(R)) was used to evaluate the data. Although the number of recovered S. suis isolates increased in the fall and winter months, most serotypes were readily isolated throughout the year; only serotypes 1, 4, 7, and 1/2 increased in frequency of isolation in the fall, winter, and spring months. The majority (61.1%) of infected pig s in this study were <12 weeks of age. More than 75% of pigs infected with serotypes 1, 6, 7, and 1/2 were < 12 weeks of age. There was exte nsive overlap in the age distributions for pigs with each serotype, an d statistically significant differences for most serotypes were not ob served. Fifty percent of pigs infected with S. suis serotypes 1 and 1/ 2 were 3-10 weeks of age, 50% of pigs infected with serotype 2 were 6- 14 weeks of age, and 50% of pigs infected with serotypes 3, 4, 5, 7, a nd 8 were 2-16 weeks of age. Isolates of S. suis were not uniformly su sceptible to penicillin, and a large percentage of isolates were resis tant to many antibiotics in common usage. The results of this study in dicated that the various serotypes of S. suis could not be readily sep arated based on antibiograms, epidemiologic factors (herd size, breed, etc.), or geographic location.