Necrotizing fasciitis infections caused by CA-MRSA noted in L.A.

August 2005

Researchers in Los Angeles have identified a number of necrotizing fasciitis (NF) infections caused by community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) occurring in a diverse group of people.

“We do not believe there are any constellations of risk factors that physicians can use to identify when MRSA is likely in any skin infection,” said Brad Spellberg, MD, lead researcher of the study and assistant professor of medicine, division of infectious diseases at Harbor-UCLA Medical Center.

Group A streptococcus, Clostridium perfringens or a combination of anaerobic and aerobic organisms cause most NF cases. In 2003, however, Spellberg and colleagues identified NF cases caused by monomicrobial bacteria.

The researchers aimed to find similar characteristics among these patients to better determine prevalence of NF caused by CA-MRSA; however, based on their review of patient medical records, they were unable to identify any risk factors that would determine who does or does not acquire NF.

“In an endemic area, you have to assume that it is MRSA until proven otherwise and you can’t rely upon lack of risk factors to say it is not MRSA,” Spellberg told Infectious Disease News. Physicians should use empirical antibiotic therapy for NF that is reliably active against locally circulating strains of MRSA, the researchers suggested.

Researching cases

Researchers noticed an influx of not just S. aureus infections from the community but also methicillin-resistant cases, which, according to Spellberg, has major implications for the antibiotics used to treat NF.

From Jan. 15, 2003, through April 15, 2004, Spellberg and colleagues identified all MRSA-positive wound cultures and reviewed patients’ medical records that showed MRSA culture growth and contained a surgical report. They reviewed the reports to determine the preoperative, intraoperative and postoperative findings and diagnosis.

Researchers included patient records in the study if intraoperative and postoperative diagnoses were NF, myositis or both. Spellberg and colleagues began with the wound culture bench and identified 843 cultures positive for MRSA. They performed a wound culture cross reference and found 14 cases of surgically confirmed NF, according to Spellberg. Patients’ ages varied from 28 to 68, and 71% of the participants were men.

Hospitalization time ranged from two to 54 days and all patients had at least one surgical procedure with the maximum being nine. Patient onset of symptoms to hospitalization was about five days.

Using pulsed-field gel electrophoresis, researchers genotyped isolates. They assigned sequence types and used polymerase chain reaction to identify genes for leukocidins, toxic shock syndrome toxin, enterotoxins A through O and exofoliative toxin a and b. A researcher blinded to the clinical details of these cases performed molecular typing at a separate site.

Diverse population

Researchers used discharge coding to identify 31 cases of NF and found that CA-MRSA caused nine (29%) cases.

MRSA bacteremia was present in four of the 10 patients who had blood cultures performed. Researchers found NF in the buttocks and/or legs of six patients, in the arms and shoulders of four patients, in the head and neck of two patients and in the trunk or abdomen of two patients.

There were no mortalities; however, all patients received combined medical and surgical therapy and had serious complications. Such complications included the need for reconstructive surgery (21%) and extended stay in the ICU (71%), according to the study. Three patients required skin grafting, and 79% needed debridement with incisions larger than 15 cm.

“Although none of the patients died, serious complications were common, including prolonged stays in the ICU, the need for mechanical ventilation and reconstructive surgery,” the researchers wrote.

“The absence of deaths in our series suggests that necrotizing fasciitis caused by community-associated MRSA may be less virulent than similar infections caused by other organisms.”

After reviewing patient history, Spellberg and colleagues also found that four of the patients were homeless and six were hospitalized sometime within the prior year. The preoperative diagnosis for eight patients indicated an abscess, five indicated NF and one indicated mediastinitis, according to the study.

“The population was very diverse,” he said. “Some patients had some risk factors and four of the patients, which was 30% of the cohort, had no coexisting conditions – no risk factors.”

Coexisting risk factors that may have predisposed patients to the infection varied from current or past injection drug use (43%), previous MRSA infection (21%), a seizure disorder (21%), diabetes (21%), chronic hepatitis C (21%), cancer (7%) and HIV/AIDS (7%), according to the study.

Wound cultures were MRSA monomicrobial in 86% (12 patients) and four of these patients had negative Gram’s stains, according to the research. Gram-positive cocci showed in nine of these patients.

All isolates were susceptible in vitro to clindamycin, rifampin, vancomycin, gentamicin and trimethoprim-sulfamethoxazole; only some were susceptible to tetracycline (10 strains), levofloxacin (five) and erythromycin (two). Physicians administered empirical therapy, such as clindamycin and vancomycin, to 10 of the patients at the time of hospitalization.

Genotype analysis consisted of five strains – three came from blood cultures and two from wound cultures – all of which had the exact same profiles for pulsed-field gel electrophoresis.

Treatment considerations

The evaluation, published in The New England Journal of Medicine, suggests that NF caused by CA-MRSA “has the potential to cause rapidly progressive disease that is clinically indistinguishable from necrotizing fasciitis caused by pathogens, such as group A streptococcus.”

Spellberg recommended that if physicians are concerned about patients potentially having NF, “make sure that empirically you add MRSA antibiotics before you get your culture results back.”

This is especially true in geographic locations where CA-MRSA is endemic, such as Los Angeles County, according to Spellberg.

For more information:

• Miller LG, Perdreau-Remington F, Rieg G, et al. Necrotizing fasciitis caused by community-associated methicillin-resistant Staphylococcus aureus in Los Angeles. N Engl J Med. 2005;352(14):1445-1453.