Objective—To investigate the prevalence of concurrent methicillin-resistant Staphylococcus aureus (MRSA) colonization in people and pets in the same household with a person or pet with an MRSA infection and to compare MRSA isolates by use of molecular techniques.
Sample Population—24 dogs, 10 cats, and 56 humans in part 1 and 21 dogs, 4 cats, and 16 humans in part 2 of the study.
Procedures—In both parts of the study, nasal swab specimens were collected from humans and nasal and rectal swab specimens were collected from household pets. Selective culture for MRSA was performed, and isolates were typed via pulsed-field gel electrophoresis (PFGE) and spa typing. Households were defined as positive when MRSA was isolated from at least 1 person (part 1) or 1 pet (part 2).
Results—In part 1, 6 of 22 (27.3%) households were identified with MRSA colonization in a person. In these households, 10 of 56 (17.9%) humans, 2 of 24 (8.3%) dogs, and 1 of 10 (10%) cats were colonized with MRSA. In part 2, only 1 of 8 households was identified with MRSA colonization in a pet. Most MRSA isolates obtained from humans and pets in the same household were indistinguishable by use of PFGE.
Conclusions and Clinical Relevance—The high prevalence of concurrent MRSA colonization as well as identification of indistinguishable strains in humans and pet dogs and cats in the same household suggested that interspecies transmission of MRSA is possible. Longitudinal studies are required to identify factors associated with interspecies transmission.
Case Description—A 2-year-old dog was evaluated because of complications that developed following tibial plateau leveling osteotomy. Infection of the surgical site developed following removal of the failed implant.
Clinical Findings—The dog was lame with evidence of a deep surgical site infection, and Staphylococcus pseudintermedius was isolated from the surgical site. Results of in vitro testing indicated that the isolate was resistant to multiple antimicrobials but susceptible to cefoxitin. Subsequent testing confirmed that the isolate was methicillin-resistant S pseudintermedius and was in fact resistant to cefoxitin.
Treatment and Outcome—On the basis of results of follow-up testing, doxycycline was administered before and after surgery to remove the surgical implant. The dog recovered without further complications.
Clinical Relevance—Findings suggested that certain strains of methicillin-resistant S pseudintermedius, which appears to be an emerging pathogen in dogs, may be falsely identified as methicillin susceptible on the basis of results of testing for cefoxitin susceptibility because cefoxitin may not induce the mecA gene as reliably in S pseudintermedius as it does in Staphylococcus aureus. Isolates of S pseudintermedius should be considered to likely be methicillin resistant when multidrug resistance is identified, even if susceptibility to some β-lactam antimicrobials is reported.
Case Description—Methicillin-resistant Staphylococcus aureus (MRSA) was isolated from the tracheostomy tube of an 18-month-old castrated male Golden Retriever in the intensive care unit (ICU) of the Ontario Veterinary College. This prompted an investigation of MRSA colonization in other animals in the ICU.
Clinical Findings—On day 1 of the investigation, MRSA was isolated from nasal swabs obtained from 2 of 10 animals (2/7 dogs and 0/3 cats), including the index case. Subsequently, MRSA was isolated from 3 of 12 animals on day 9; 3 of 9 animals on day 13; and none of 14, 5, and 6 animals on day 20, 27, and 78, respectively. Overall, MRSA was isolated from 6 of 26 (23%) animals during the outbreak period (4/22 dogs and 2/4 cats). The apparent incidence of MRSA acquisition in the ICU from days 1 through 13 was 20% (5/25 animals). No clinical signs of MRSA infections developed. All isolates were indistinguishable from one another.
Treatment and Outcome—Infection-control measures including active surveillance of all animals in the ICU, barrier precautions, and hand hygiene were used to control the apparent outbreak.
Clinical Relevance—Methicillin-resistant S aureus is an emerging problem in veterinary medicine. Intensive care units may be at particular risk for periodic outbreaks of colonization and disease. The outbreak of this report highlights the potential for clinically inapparent transmission of MRSA within a facility; infection-control measures that might facilitate MRSA eradication should be considered in ICU settings.
Objective—To compare methicillin-resistant Staphylococcus pseudintermedius (MRSP) and methicillin-susceptible S pseudintermedius (MSSP) infections in dogs.
Design—Multicenter case-control study.
Animals—Dogs with MRSP infections were matched, by hospital, with 2 MSSP controls, with the infections occurring immediately before and after the case infection.
Procedures—Signalment, historical, clinical, treatment, and outcome data were documented. Conditional logistic regression was performed. A manual stepwise backward elimination procedure was used to build the multivariable model.
Results—56 case and 112 control dogs were enrolled. Pyoderma was the most common infection type in both groups. In the final multivariable model, systemic administration of antimicrobials within 30 days prior to infection was significantly associated with an MRSP versus an MSSP infection (OR, 9.9; 95% confidence interval, 3.59 to 27.53).
Conclusions and Clinical Relevance—The association of prior antimicrobial administration and MRSP infection indicated the potential impact of routine antimicrobial use in veterinary medicine on antimicrobial resistance and the need for prudent use of these important drugs. Mortality rate was not significantly different between MRSP and MSSP infections; the lack of a significant difference suggested that MRSP was inherently no more virulent than MSSP, provided the infection was properly diagnosed and appropriate treatment was started. Basic concepts such as prudent antimicrobial use and early diagnosis through timely submission of appropriate culture specimens therefore can be important measures to try to reduce the impact of this pathogen.