MRSA, MRSE infection in joint replacement

Among 9000 patients screened preoperatively at one U.K. center, the MRSA carrier rate was 1%.

BIRMINGHAM, England — Orthopaedic surgeons who perform total joint arthroplasties regularly wage a battle against methicillin-resistant Staphylococcus aureus infection.

To help them better understand this bacterial infection and more effectively screen for, diagnose and treat it, the British Hip Society held a symposium on the subject during the British Orthopaedic Association Annual Congress, here.

“Methicillin-resistant S. aureus (MRSA) is something that causes fear and trembling among the general public,” said moderator Geoff Ridgway, MD, FRCP. And, it causes an equal amount of consternation among clinicians because frequently MRSA cannot be treated with a chemical sporine, said Ridgway, a consultant microbiologist at The London Clinic.

Methicillin-resistant Staphylococcus epidermis, or MRSE, another bacterial infection causing orthopaedists concern, was also addressed during the symposium. “It’s not an acute pathogen. It’s an insidious pathogen,” Ridgway said. Although part of normal skin flora, it turns problematic when any normal flora gets transferred elsewhere in the body, like the bowel or bladder. “So you have a problem when the long-term load rate colonization may become infection of periprosthetic joints,” he said.

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Methicillin-resistant Staphylococcus aureus bacteria caused this cutaneous abscess on a patient’s thigh. S. aureus and S. epidermis are commonly found on the skin. Not always problematic, over time they have grown resistant to antibiotics like methicillin, oxacillin, penicillin and amoxicillin. Researchers are devising new and better ways of fighting them, even without antibiotics, in and out of the operating room

Source: Centers for Disease Control (CDC)

Increased infection incidence

Orthopaedic surgeon Peter K. Kay, FRCS, of Wrightington Hospital, Wigan, England, said that even with clean operating rooms, increased access to antibiotics, and advanced technology for dealing with these infections, actual rates may reach 8%, according to the British government. Such infections now cost more than $1.74 million annually, he noted.

Kay estimated actual infection rates at between 1% and 4%, but said some studies underestimated them or did not include length of follow-up. “Even the national joint replacement registry underestimates infection as they rely only on revision as an endpoint, which could put the real infection rate somewhere up to 4%.”

MRSA and coagulase-negative staphylococcus (CNS) infections often develop late, up to 12 years postoperatively.

In a Wrightington Hospital study of 1500 hip replacements with 17-year follow-up, the three-month postop infection rate was 0.8% per year, increasing to 1.67% at 17 years. “The longer you went in years, the more infection developed,” Kay said. When someone tells you their infection rate ask about the length of follow-up.

FACTS ABOUT MRSA
  • As early as 1960, strains of methicillin-resistant Staphylococcus aureus (MRSA) were identified through a gene mutation. European hospitals started reporting MRSA outbreaks during that decade.
  • S. aureus can cause a range of diseases, including osteomyelitis, pneumonia and endocarditis.
  • At least 25% of nosocomial infections reported in the United States can be traced to MRSA.
  • The numbers of community-acquired MRSA rates are soaring, with cases now being reported in individuals with no known risk factors.

Source: 2001 New York University School of Medicine Study

Contamination control

He recommended being diligent in keeping contaminating bacteria out of the operating field during primary hip or knee replacements. “We can’t live without infections in orthopaedics, so what we’ve got to work out is how we’re going to manage it prospectively.”

Kay reviewed likely sources of contamination and research that suggested most infections stemmed from surgical site infection.

“We’ve got to keep the bugs out of the wound in the first place as well as use appropriate antibiotics.”

Kay also discussed theater design, systemic antibiotics and cementing implants with antibiotic-impregnated bone cement as the “three pillars” for reducing infections in total joint arthroplasty (TJA). “You can significantly reduce the infection rate with these three pillars. If you pick two of them you’ll get a great response, but then the third one is difficult to justify and prove.”

Antibiotics remain effective weapons. “What we’ve seen is that general antibiotics can reduce infection rates from 7% to 10%, when nothing was done, down to about 1%.

“Having antibiotics in your cement could also reduce infection rates, despite the fact that maybe some of the antibiotics aren’t the best antibiotics against staph.”

Reducing bacteria

Investigators in Manchester at Wrightington recently studied intraoperative bacterial contamination of skin, surgical gowns and gloves in 125 TJA surgeries. Of 750 samples analyzed, 73% were contaminated. They grew bacteria from some wound sites, the operative field or around the operated site. Even unexpected locations, like light bulbs or equipment handles, became bacterial sources.

“What was worrisome was that 10% of the cases seemed to be deeply contaminated because the needle that passed through the deep fascia at the end of the procedure grew bacteria.”

Researchers also found 10% contamination of femoral heads removed at the beginning of the procedures for bone banking purposes. Most were infected with CNS.

Large study

Recently, in screening 9000 patients at Wrightington Hospital, investigators detected MRSA in about 1% of patients coming in for clean orthopaedic surgery, Kay said.

Among the 2510 samples studied from wounds, infected joints — even the tips of surgical screws — 33% were positive for bacteria; 4.6% grew S. aureus. From that group, they identified 9.8% as MRSA. “But what was really worrying or concerning is that 43% of the samples … grew S. epidermis. But 55%, more than half of the S. epidermis that we were growing, was resistant to methicillin. … This multi-resistant S. epidermis is a problem that keeps coming up.”

Pathologists, orthopaedists and researchers still have much to learn before they fully understand MRSA, MRSE and CNS. “We really need to look at other therapies beyond antibiotics to control infection,” Kay said.

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Bacteria can hide on implanted devices and later become problematic. This 2005 electron micrograph shows large numbers of Staphylococcus aureus bacteria found on the luminal surface of an indwelling catheter. Keeping S. aureus out of the OR and the wound should be an orthopaedist’s priority.

Source: CDC/Janice Carr

For more information:
  • Kay PK. Symposium: Infection in total hip replacement: the battle with MRSE and MRSA — Understanding the enemy. Presented at the British Orthopaedic Association Annual Congress. Sept. 20-23, 2005. Birmingham, England.
  • Davis N, Curry A, Gambhir AK, et al. Intraoperative bacterial contamination in operations for joint replacement. J Bone Joint Surg Br. 1999;81-B:886-889.
  • Mohanty SS, Kay PR. Infection in total joint replacements — Why we screen for MRSA when MRSE is the problem. J Bone Joint Surg Br. 2004;86-B:266-268.