Molecular Diagnosis of SSTIs May Yield Better Clinical Outcomes

Molecular diagnostics such as polymerase chain reaction (PCR)—based tests provide faster, more complete results than traditional culture-based tests, and their use may improve outcomes for patients with chronic wounds and skin and soft tissue infections (SSTIs), according to new findings presented at the 21st Annual MAD-ID Meeting held May 9 to 12 in Orlando, Florida.

About 6.5 million individuals were afflicted with chronic wounds and SSTIs in the United States in 2009.¹ The costs of treating associated complications reached upward of $25 billion at that time. A more recent study estimated that annual Medicare spending for all wound types ranged from $28.1 billion to a whopping $96.8 billion in 2014.²

“These costs could potentially be mitigated with the use of rapid diagnostics that have the capability to better identify wound pathogens and thus allow clinicians to provide better clinical care through targeted antimicrobial therapy,” said Tanya Moreno, PhD, vice president of research and development at Millennium Health, citing a Mayo Clinic Proceedings article on the hospitalists’ view of treating SSTIs.³

To test this hypothesis, a team of investigators from CogenDx, Millennium Health’s genetics brand in San Diego, California, led by Dr. Moreno, conducted a retrospective evaluation of real-time PCR-based identification of organisms in chronic wounds at 3 outpatient wound care clinics. Consenting patients with chronic wounds, open wounds, or SSTIs undergoing standard care were eligible to participate.

For each enrolled patient (n = 186), 4 specimens were collected from the wound bed: 1 for standard culture and 3 for PCR-based testing (a tissue specimen and 2 swabs—1 collected before and 1 after debridement—and tissue after debridement). Real-time PCR was performed on the specimens, and the results were compared with a standard culture report from the reference microbiology laboratory.

“Results in this cohort suggest that a significant number of organisms may be underreported by being categorized as mixed flora by culture,” said Roger Schechter, MD, the principal investigator, who discussed the results with Contagion^®. “This is influenced by clinical lab culturing guidelines and the labor-intensive nature of culturing many different organisms from a single wound. It may also be due to a lack of an order for that culture type by the physician.”

In 62% of cases in which mixed flora was reported by culture, the PCR-based test (DxWound) identified potentially pathogenic organisms. The investigators concluded that molecular diagnosis of SSTIs may provide advantages for clinical treatment compared with culture-based methods.

Sandy Estrada, PharmD, associate director of clinical affairs for CogenDx, who presented the study results at MAD-ID, shared further details with Contagion^®. “Knowing that wound infections are common, complicated, costly and consequential, it would be beneficial to rapidly and effectively target therapy both in cases where broadened therapy may be needed [and] where antimicrobial streamlining is warranted,” she said.

Although recommendations for treating SSTIs advise identifying the pathogenic organisms to guide antibiotic use, standard techniques are time-consuming and may not correctly identify the pathogen, according to Estrada. “Typically, infections are diagnosed by culture-based techniques combined with biochemical testing and Gram staining to identify microbes present in the wound,” she said. “These approaches require 3 to 5 days but can take longer for difficult-to-grow organisms—for example, up to 6 weeks for fungus—and may not be comprehensive.”

Appropriate initial therapy is essential in treating SSTIs and relies on proper identification. Broad-spectrum antimicrobial therapy is often prescribed pending final culture results, increasing the prevalence of drug-resistant organisms. Delayed initiation of the optimal regimen is an independent risk factor for SSTI treatment failure.^3,4 An Infectious Diseases Society of America public policy outlines the need for improved diagnostics for infectious diseases, stating: “New tests are needed that can identify specific pathogens or, at a minimum, distinguish between bacterial and viral infections and also provide info on susceptibility to an antimicrobial agent.”⁵

DxWound is a DNA-based tool that provides a rapid, comprehensive assessment of the wound microbiome providing a single report that includes detected aerobes, anaerobes, fungi, antibiotic resistance genes and a virulence gene and may help clinicians rapidly target antimicrobial therapy for patients with suspected wounds or skin and soft tissue infections. DxWound may be utilized in many different wound infection clinical scenarios, such as cases of empiric treatment failure, suspicion of fungal, anaerobic or MDR organisms or history of antibiotic resistance or intolerance.

References

1. Sen CK, Gordillo GM, Roy S, et al. Human skin wounds: A major and snowballing threat to public health and the economy. Wound Repair Regen. 2009;17(6):763-771. doi:10.1111/j.1524-475X.2009.00543.x.
2. Nussbaum SR, Carter MJ, Fife CE, et al. An economic evaluation of the impact, cost, and Medicare policy implications of chronic nonhealing wounds. Value Health. 2018;21(1):27-32. doi: 10.1016/j.jval.2017.07.007.
3. Amin AN, Cerceo EA, Deitelzweig SB, Pile JC, Rosenberg DJ, Sherman BM. Hospitalist perspective on the treatment of skin and soft tissue infections. Mayo Clin Proc. 2014;89(10):1436-1451. doi: 10.1016/j.mayocp.2014.04.018.
4. Ruhe JJ, Smith N, Bradsher RW, Menon A. Community-onset methicillin-resistant Staphylococcus aureus skin and soft tissue infections: impact of antimicrobial therapy on outcome. Clin Infect Dis. 2007;44(6):777-784. doi: 10.1086/511872.
5. Stevens DL, Bisno AL, Chambers HF, et al; Infectious Diseases Society of America. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the Infectious Diseases Society of America. Clin Infect Dis. 2014; 59(2): e10-52. doi: 10.1093/cid/ciu444.