1. Staph aureus with cefazolin: SUSCEPTIBLE. This report means that the isolated bacteria is sensitive to the first generation cephalosporin. It means that the organism is most likely MSSA and it is appropriate to treat the infection with cephalexin (Keflex), a first-generation cephalosporin.
2. Staph aureus with cefazolin: RESISTANT. This report indicates MRSA and one should treat it with doxycycline, clindamycin, trimethoprim/sulfamethoxazole or linezolid for oral therapy, or vancomycin, linezolid, daptomycin (Cubicin, Cubist Pharmaceuticals) or tigecycline (Tygacil, Pfizer) for IV therapy, based on the culture and sensitivity report.
3. Coagulase-negative Staphylococcus. This is a common skin flora and rarely a disease-causing agent. This could mean one of two things. You may not have taking a good enough culture sample to isolate the disease-causing bacteria. Alternately, this finding could mean the wound is not infected but is perhaps red and inflamed from other reasons. For example, one may consider an allergic reaction to the wound dressing.
Pertinent Insights On Diagnosing And Treating Infected Wounds
Any open wound is a portal of entry for bacteria and there is a possibility of wound infection, oftentimes with gram-positive bacteria, such as Staphylococcus or Strep species. It is very important to diagnose and treat these conditions swiftly in order to achieve optimal outcomes. Accordingly, our expert panelists explore how to diagnose and treat wound infections, offering a variety of insights on antibiotics and culturing.
How do you identify and diagnose wound infection?
Kazu Suzuki, DPM, CWS, advises students to use their senses to detect infection. He says one must hear (patient complaints of pain), see (redness and swelling), touch (swelling and skin changes) and smell (infected wounds). He directs the most attention to the patient’s complaint of wound pain. If the wound pain increases for any reason, he says one must suspect infection as the top reason for the increased amount of pain. Dr. Suzuki notes that even patients with profound diabetic neuropathy can experience wound pain in the face of infection.
Although blood test results (such as white blood count, sedimentation rate and C-reactive protein) can be helpful, Dr. Suzuki considers those tests markers of infection rather than definitive diagnostic tools of wound infection. For example, he monitors those lab values for a response to the antibiotics prescribed to a particular patient. He treats many patients with diabetes, cancer patients (on chemotherapy) and transplant patients (on immunosuppressive medications) so it is not uncommon to see completely “normal” lab values when these patients have an active wound infection.
Based on their observational data of wound infections, Dr. Suzuki cites Sibbald and colleagues for the mnemonics of NERDS (superficial infections that should be treated with topical antimicrobials) and STONEES (deep infection that should be treated with systemic antibiotics).1 NERDS means Non-healing, Exudate, Red + Bleeding, Debris, Smell. STONEES means Size is bigger, Temperature, Os (exposed bone), New breakdown, Exudate, Erythema and Edema, and Smell.
Warren Joseph, DPM, FIDSA, uses clinical signs and symptoms to diagnose a wound infection. As a member of the Infectious Diseases Society of America (IDSA) Diabetic Foot Infection Guidelines Committee, he has investigated the literature on the topic in order to make evidence-based recommendations.
“Nothing has convinced us to change thinking between our original 2004 guidelines and the newly revised document (to be published in late 2011 or early 2012)” notes Dr. Joseph. He says the 2004 guidelines emphasize clinical signs and symptoms as being key to the diagnosis of a wound infection.2 Along with the classic “primary” signs including redness, swelling and heat, Dr. Joseph cites the possibility of “secondary” signs such as poor quality of granulation tissue, increased drainage, tunneling and odor.
Kathleen Satterfield, DPM, says a frank infection “is really no problem” as far as the diagnosis goes. She says the real problem is with the infection that is on the edge, especially the one with no portal or a small portal of entry. To complicate things, Dr. Satterfield notes that patients with diabetes can have leukocyte dysfunction and, as a result, are sometimes unable to mount a response to a localized or even systemic infection. These patients may not have a high white blood cell count or a fever.
“That is when you have to rely on clinical experience and if you do not have that yet, you seek out others who do have that gray hair. You do not want to learn by catastrophe,” says Dr. Satterfield.
Dr. Satterfield says it may be helpful to go back to the basics and look for rubor, calor and tumor but on a localized basis. If the patient has localized redness, heat and edema, she says you are probably dealing with an infection.
What is your empiric choice of antibiotics in the outpatient setting?
Although Dr. Satterfield says broad spectrum antibiotics are the safe choices, she notes that clinicians have become smarter about what organisms they are going to find. She questions whether it is unsafe to just use a first generation cephalosporin empirically for uncomplicated foot infections when Staph aureus is reportedly the number one organism found in uncomplicated foot infections. When it comes to mild outpatient infections, Dr. Satterfield notes that physicians will be seeing the patient back in a week.
When considering antibiotics, Dr. Joseph questions the location and appearance of the infection. He asks if the patient is predisposed to methicillin-resistant Staph aureus (MRSA) following a previous infection and considers the local rates of MRSA prevalence. If he suspects MRSA, Dr. Joseph prefers doxycycline 100 mg BID. Likewise, for outpatient wound patients, Dr. Suzuki prefers using doxycycline 100 mg BID for seven to 10 days, saying the oral medication covers most MRSA infections with minimal side effects and drug interactions.
Although some clinicians have suggested high-dose trimethoprim/sulfamethoxazole (Bactrim, Roche) or two pills of trimethoprim/sulfamethoxazole DS BID for seven to 10 days, Dr. Suzuki has had better outcomes and much less drug interaction issues with doxycycline. Likewise, Dr. Joseph avoids trimethoprim/sulfamethoxazole because of its adverse event profile. If he does not suspect MRSA but does suspect MSSA or Streptococcus, he would consider cephalexin.
Many of Dr. Suzuki’s patients are on warfarin (Coumadin) for atrial fibrillation and other conditions. He notes that trimethoprim/sulfamethoxazole is contraindicated for those patients on this common anti-coagulation drug. Dr. Suzuki notes levofloxacin (Levaquin, Janssen Pharmaceuticals) can be effective for some MRSA infections but he prefers to reserve levofloxacin for more serious gram-negative infections such as Pseudomonas. He has seen several cases of Achilles tendon ruptures after the patients took ciprofloxacin (Cipro, Bayer) and levofloxacin so Dr. Suzuki suggests reserving the quinolone class of drugs for serious infections only. Dr. Joseph agrees and suggests that one not rely too heavily on the quinolones.
What is your empiric choice of antibiotics for hospitalized patients with infected wounds?
Dr. Suzuki often starts the IV antibiotic therapy with a combination of vancomycin and piperacillin/tazobactam (Zosyn, Pfizer), which he readjusts based on wound culture sensitivity results. He will consult the infectious disease doctors on staff for antibiotic management, especially if the patients are immunocompromised or if they need long-term antibiotics with a peripherally inserted central catheter (PICC) line for bone infection treatment.
For moderate to severe infections as defined by the IDSA guidelines, Dr. Joseph generally practices “de-escalation” therapy. He starts with a combination effective against MRSA and then changes this based on culture results. His usual empiric choice is a combination of ertapenem and vancomycin. Although he formerly used piperacillin/tazobactam in place of ertapenem, Dr. Joseph says one almost never needs the anti-Pseudomonal activity of piperacillin/tazobactam and ertapenem can be a once daily dose. He will also substitute linezolid for vancomycin in appropriate patients.
With a hospitalized patient has a serious infection, Dr. Satterfield says her facility’s clinicians are bound to following hospital protocol. On a recent conference call, she contacted Dr. Joseph via Skype and they discussed hospital antibiograms. She notes the antibiograms reveal the most common organisms in that particular hospital and after admitting the patient, one treats to the antibiogram. “(Dr. Joseph) said something amazing to me,” she recalls, “that many doctors don’t realize an antibiogram exists. That is your roadmap for treatment.”
When do you consider taking a wound culture and how?
Dr. Joseph will culture a wound that appears infected but will not culture clinically non-infected wounds. Saying he does not believe in superficial swabs, Dr. Joseph notes deep tissue or surgical cultures are the most reliable. He says one can use “semi-quantitative” swab methods, such as the “Levine technique.”3 As he explains, with this technique, one rolls a swab with pressure over a 1 cm2 area of a debrided and cleansed wound. Dr. Joseph says this allows the capture of deeper wound fluid.
Except for a mild or very superficial wound infection, Dr. Suzuki prefers to take a wound culture using a swab prior to initiating an antibiotic therapy. In his outpatient wound clinic, he debrides the wound first, irrigates it well with sterile saline and then takes a piece of tissue from the wound bed for tissue culture. In an operating room setting, he uses the same method to take deep tissue samples, including a piece of bone or bone marrow if he suspects bone infection.
On a few occasions, Dr. Suzuki says one may not be able to get a good tissue culture or the portal of entry is not obvious. In these cases, he would still use empirical antibiotics and follow the clinical course closely. To that end, Dr. Suzuki checks the wound daily in hospitalized patients or every other day to a few days in the outpatient clinic.
Dr. Satterfield would not consider taking a wound culture. As she notes, the consensus preference of her physicians at her institution is taking a wound biopsy for culture when there is an open portal. However, Dr. Satterfield says this doesn’t seem to be standard practice among podiatrists yet.
“I still hear about people taking a swab culture from the surface of the wound without prepping the wound. That is worthless,” claims Dr. Satterfield.
Dr. Satterfield notes if the wound has purulent drainage, it is all right to take a culture from deep inside the wound, getting some of the purulence after thoroughly cleansing the outer surface of the wound. However, she says in order to obtain the most optimal culture, she recommends cleansing the wound with an agent like Hibiclens (Molnlycke Health Care), debriding away the surface tissue and then sending a deep tissue culture.
When would you consider admitting a patient for wound infection?
Dr. Satterfield says one must admit patients for IV antibiotics, wound biopsy/culture, I&D of a wound, debridement of a wound and to get studies and consults that would otherwise not be efficiently available outside of the hospital.
One should admit patients who have failed outpatient therapy, when they need significant surgical intervention/incision and drainage, when IV antibiotics are necessary or when the patient is metabolically unstable and systemically unwell, according to Dr. Joseph. He says these patients would fall under the IDSA definition of having a “severe” infection.
For Dr. Suzuki, admitting a patient depends on the clinical findings and the overall medical status of the patient. When he encounters the new onset of cellulitis on a lower extremity wound, he draws a line with a surgical marking pen along the erythema demarcation line. Then he would recommend admission for IV antibiotics if the erythema is not receding as it should with oral antibiotics. Dr. Suzuki also recommends admission if a patient complains of high fever or chills as these may be early signs of sepsis.
In addition, Dr. Suzuki would be more inclined to recommend admission if a patient is older or sicker. For example, he would consider admitting a patient who is 70 years or older, one with any comorbidities such as diabetes or cancer, or a patient who is immunocompromised or immunosuppressed for organ transplant.
The last reason for admitting a patient to the hospital is to control pain but Dr. Satterfield notes this does not usually come into play for infected wounds because podiatrists are often treating patients with diabetic neuropathy. In Dr. Satterfield’s experience, patients with wound infections often have a vascular-related issue that led to the infection so she advises obtaining a consult for vascular studies. Since one cannot efficaciously get a vascular consult outside the hospital, she suggests getting a consult in house within a day or two.
Dr. Satterfield says another advantage to hospital admittance is being able to refer the patient with an infected extremity for possible limb reperfusion as this may prevent a transmetatarsal amputation or an even higher amputation in these patients.
Dr. Joseph is a consultant in lower extremity infectious diseases and a Fellow of the Infectious Diseases Society of America. He is affiliated with Roxborough Memorial Hospital in Philadelphia.
Dr. Satterfield is the Director of Medical Education at the Western University College of Podiatric Medicine in Pomona, Calif. She is a Fellow and President-Elect of the American College of Foot and Ankle Orthopedics and Medicine.
Dr. Suzuki is the Medical Director of the Tower Wound Care Center at the Cedars-Sinai Medical Towers. He is also on the medical staff of the Cedars-Sinai Medical Center in Los Angeles and is a Visiting Professor at the Tokyo Medical and Dental University in Tokyo, Japan.
1. Sibbald RG, Goodman L, Woo KY, et al. Special considerations in wound bed preparation 2011: an update. Adv Skin Wound Care. 2011; 24(9):415-36.
2. Lipsky BA, Berendt AR, Deery HG, et al. Diagnosis and treatment of diabetic foot infections. Clin Infect Dis. 2004; 39(7):885-910.
3. Levine NS, Lindberg RB, Mason AD Jr, et al. The quantitative swab culture and smear: a quick, simple method for determining the number of viable aerobic bacteria on open wounds. J Trauma. 1976;16(2):89-94.
For further reading, see “How To Differentiate Between Infected Wounds And Colonized Wounds” in the July 2005 issue of Podiatry Today or “Essential Insights On Addressing Common Wound Dilemmas” in the November 2009 issue.