Case-control study of Staphylococcus lugdunensis infection isolates from small companion animals.

Background: Coagulase-negative Staphylococcus lugdunensis has recently been shown to cause invasive infections of people, which are similar in pathogenic effect to those caused by Staphylococcus aureus. Little is known about the pathogenicity of S. lugdunensis in companion animals.

Objectives: To compare potential risk factors for infection, body sites affected, and whether cases and controls had been treated with antimicrobial drugs based upon susceptibility test results.

Animals: Thirty-three cases of S. lugdunensis infection (25 dogs, six cats and two small mammals) were identified between January 2003 and August 2011. Two Staphylococcus pseudintermedius controls, which were identified by the microbiology laboratory immediately before and after each S. lugdunensis case, were host-species matched to each case.

Methods: A retrospective case-control analysis.

Results: During the period evaluated, the prevalence of S. lugdunensis infection was 1.3 cases per 10,000 hospital admissions for dogs and 0.95 cases per 10,000 admissions for cats (P = 0.453). In univariate analyses, S. pseudintermedius isolation was significantly associated with skin infections (P < 0.0001), while S. lugdunensis isolation was associated with the respiratory tract (P = 0.03) and other deep tissues (P = 0.005). Cases were less likely than controls to have been treated based upon susceptibility test results (P = 0.02). A conditional logistic regression analysis showed isolation of S. lugdunensis to be associated with recent (≤ 30 days) steroid administration (odds ratio, 17.72; 95% confidence interval, 2.35-132.82; P = 0.005); and in-patient status (odds ratio, 9.67; 95% confidence interval, 2.18-42.88; P = 0.003).

Conclusions: These results suggest that S. lugdunensis may cause invasive infections in companion animals, which should be treated with antimicrobials based upon susceptibility tests when available.