High prevalence of S. aureus carriage in HCWs contributed to outbreak
A recent outbreak of Staphylococcus aureus surgical site infections after cardiovascular surgery at a Toronto hospital was associated with a high prevalence of S. aureus carriage among health care workers.
“Control of S. aureus infections is a challenge as the organism can be part of the patient’s own flora,” Manal Tadros, MD, PhD, of the department of microbiology at the University of Toronto, told Infectious Disease News. “A well-established surveillance system, including post-discharge surveillance, is important for early recognition of trends and outbreaks.”
The outbreak occurred from January 2009 to March 2010, when 38 patients developed an S. aureus surgical site infection. Pulsed-field gel electrophoresis showed that the outbreak involved three different strains of S. aureus, two of which were methicillin-sensitive and one that was methicillin-resistant. The researchers conducted a retrospective case-control study to identify risk factors contributing to the outbreak.
Twelve of the 38 cases were attributed to MRSA, of which nine were associated with the MRSA outbreak clone. There were 14 cases of MSSA that were attributed to the two MSSA outbreak clones. Twelve of the cases did not have an outbreak clone and three did not undergo typing. Among the 256 health care workers who were tested, 74 were colonized with S. aureus, of whom 21 were carrying one of the outbreak strains.
The researchers observed that there were opportunities for improvement in infection control practices, such as hand hygiene and routine practices. There were also issues with the processes in the operating room, such as inconsistent use of preoperative chlorhexidine showers, occasional hair clipping inside the operating room, occasional suboptimal timing of preoperative antimicrobial prophylaxis and reducing traffic flow in the operating room.
Previous cardiac surgery and longer procedure duration were associated with S. aureus surgical site infections.
“In addition to enforcing best practice guidelines, screening and decolonizing staff carrying the outbreak strains was important to controlling this outbreak,” Tadros said. “Enhanced attention was paid to improving surgical and post-operative wound care to reduce the risk of infection. Prior to cardiac surgery, our patients are now being screened for S. aureus and decolonized if positive.”