Tag Archive | MSSA

Detecting Pathogens in Pediatric Infections: Swab, Tissue, or Bottle?

Identifying the pathogenic microorganism in childhood osteomyelitis and septic arthritis is essential to tailoring appropriate treatment. But the traditional methods of swab and tissue culturing have subpar success rates in pediatric patients, identifying the pathogen in only 40% to 60% of cases. In the October 21, 2020 edition of The Journal, Shin et al. report their findings comparing microbial identification rates using pediatric blood culture bottles (BCBs), typical culture swabs, and tissue specimens.

Over 3 years, the authors prospectively collected intraoperative specimens from 40 pediatric patients (mean age of 7.2 years) who underwent surgery for a presumed osteoarticular infection. Half of the patients had received oral or intravenous antibiotics in the 3 weeks prior to surgery, while the other half had received intravenous cefazolin after culture specimens were obtained in the operating room. Intraoperative culture specimens were obtained in 3 different manners for all patients:

  1. Four 21-gauge needles were dipped into the infected fluid and were used to inoculate 4 pediatric BCBs – 2 aerobic and 2 nonaerobic.
  2. Two swabs were placed in direct contact with the infected tissue.
  3. Two solid tissue samples were collected and placed in 2 sterile containers.

In these 40 cases, the microbial identification rate of the BCB method was 68%, compared to 45% with the swab method and 38% with the tissue method—all statistically significant differences. In 9 patients (23%), the pathogen was only identified with the BCB method. No samples showed positive culture growth with the other 2 methods if the BCB culture was negative. Interestingly, in a subgroup analysis of 15 patients with methicillin-susceptible Staphylococcus aureus (MSSA), the authors found no difference in detection rates between the 3 methods, but in cases involving organisms other than MSSA, detection with BCBs was significantly higher than with both swab and tissue cultures.

The apparent superiority of BCBs to detect microbial organisms could be due to the characteristics of pediatric BCBs, which enhance microorganism growth in a small amount of liquid. Although there are some concerns that this enhanced BCB detection could lead to increased rates of false-positives from contaminants, I think the risk of false positives is a viable tradeoff if we can more quickly and accurately identify pathogens in pediatric infections. As Shin et al. emphasize, “Sequelae resulting from these infections are particularly unfortunate for pediatric patients.”

Matthew R. Schmitz, MD
JBJS Deputy Editor for Social Media

Surgical Infection Prevention: Local Antibiotic Powders Beat IV Agents in Rats

Culture for OBuzzWhen it comes to preventing infections associated with orthopaedic procedures, the question of which antibiotic to use is only one of several concerns. How and where to administer antibiotics is another relevant question, not only in terms of infection-fighting effectiveness but also in terms of combatting the proliferation of antibiotic-resistant microbes.

In the September 19, 2018 issue of The Journal of Bone & Joint Surgery, Sweet et al. report on findings from a study in rats that compared the infection-prevention efficacy of intravenous (IV) cefazolin (n = 20) and IV vancomycin (n = 20) with local application of 4 antimicrobials—vancomycin powder (n = 20), cefazolin powder (n = 20), tobramycin powder (n = 20), and dilute Betadine lavage (n = 20).

The researchers induced infection by surgically implanting a polytetrafluoroethylene vascular graft near each rat’s thoracic spine and inoculating it with methicillin-sensitive Staphylococcus aureus (MSSA). After 7 days, all of the rats in each of the IV cefazolin, IV vancomycin, and Betadine lavage groups had grossly positive cultures for MSSA, “with bacterial colonies too numerous to count.” Ninety percent of the rats in the local cefazolin-powder group also had positive cultures, but the infection rates with vancomycin and tobramycin powder were much lower than those with the other four approaches (p <0.000001).

In addition to the main “disclaimer” about this study (namely, that its findings cannot be extrapolated to clinical practice in humans), the authors caution that “the effect of locally applied antibiotics on the emergence of resistant organisms is unknown,” while citing evidence that systemic administration of antibiotics is “associated with the emergence of resistant organisms at an alarming rate.”

Sweet et al. say they plan to follow up this study with a similar model to investigate the efficacy of local antimicrobials against the more problematic methicillin-resistant Staphylococcus aureus (MRSA)—and they suggest further that “clinical studies should be considered to determine the relative clinical efficacy of local versus systemic antibiotics for surgical infection prophylaxis in humans.”

Modern Irrigation/Debridement Yields Good Results for Early Post-THA Infection

Hip Debridement for OBuzzNowadays, chronic deep periprosthetic joint infections (PJIs) are typically treated with 2-stage exchange arthroplasty, but what about acute PJIs? In the December 6, 2017 edition of JBJS, Bryan et al. report on a retrospective cohort study of acute infections after hip arthroplasty. The results suggest we’ve come a long way in identifying patients with early infections and that contemporary irrigation-and-debridement protocols are more successful than older methods.

The researchers studied 6-year outcomes in 90 hips that had undergone either total or hemiarthroplasty and that were determined to have either acute early postoperative infections (n=66) or acute hematogenous infections (n=24). All the infected hips were managed with either irrigation, debridement, and modular head and liner exchange (70%) or with irrigation and debridement alone (30%). The authors stratified the patients into those without comorbidities (A), those with 1 or 2 comorbidities (B), and those with >2 comorbidities (C). Postoperatively, patients were treated with broad-spectrum intravenous antibiotics, followed by targeted therapy administered by infectious disease specialists.

Of the 90 acute infections, failure—defined as uneradicated infection, subsequent removal of any component for infection, unplanned second wound debridement for ongoing infection, or infection-related mortality—occurred in 15 hips (17%). Of those 15, 9 required component removal. The chances of treatment failure were slightly higher in cases of hematogenous infection (21%), compared with acute early postoperative infection (15%), but that difference was not statistically significant. Significant comorbidity-related failure-rate differences were found: failure occurred in 8% of the grade-A patients, 16% of grade-B patients, and 44% of grade-C patients. The most common infecting organism was methicillin-sensitive Staphylococcus aureus (MSSA).

From this overall 6-year success rate of 83%, the authors conclude that “with modern inclusion criteria for acute infection, modern surgical techniques, and modern antibiotic therapy…the rate of success was higher than in most historic reports.”

JBJS Case Connections: Strange and Dangerous Spinal Infections

Infections of the spine are particularly challenging to orthopaedists because they often present emergently, can be difficult to diagnose precisely, and can have catastrophic or fatal outcomes if not treated effectively.The September 23, 2015  “Case Connections” from JBJS Case Connector discusses five cases of rare but serious spinal infections.

The “Case Connections” springboards from a September 9, 2015 JBJS Case Connector case report by Rosinsky et al. that describes a sixty-five-year-old man who presented with fever and intractable lumbar pain that radiated to his right leg. In this case, a methicillin-susceptible Staphylococcus aureus (MSSA) infection had formed a large lobulated epidural abscess at L4-S1, with paraspinal muscle and intradural extension. One year after an L3-S1 laminectomy and two follow-up surgeries to treat hematomas and repair dural perforations, the patient was neurologically intact and walking independently.

The Rosinsky et al. case and the three other relevant “connections” from the JBJS Case Connector archive emphasize that prompt, definitive diagnosis and treatment of spinal infections–and enlisting the expertise of infectious-disease specialists–can lead to positive outcomes, while delay and clinical confusion can end catastrophically or fatally.