Mycological culture is the traditional method for identifying infecting agents of onychomycosis despite high false-negative results, slower processing, and complications surrounding nondermatophyte mold (NDM) infections. Molecular polymerase chain reaction (PCR) methods are faster and suited for ascertaining NDM infections.
To measure agreement between culture and PCR methods for identification of infecting species of suspected onychomycosis, single toenail samples from 167 patients and repeated serial samples from 43 patients with suspected onychomycosis were processed by culture and PCR for identification of 16 dermatophytes and five NDMs. Agreement between methods was quantified using the kappa statistic (κ).
The methods exhibited fair agreement for the identification of all infecting organisms (single samples: κ = 0.32; repeated samples: κ = 0.38). For dermatophytes, agreement was moderate (single samples: κ = 0.44; repeated samples: κ = 0.42). For NDMs, agreement was poor with single samples (κ = 0.16) but fair with repeated samples (κ = 0.25). Excluding false-negative reports from analyses improved agreement between methods in all cases except the identification of NDMs from single samples.
Culture was three or four times more likely to report a false-negative result compared with PCR. The increased agreement between methods observed by excluding false-negative reports statistically clarifies and highlights the major discord caused by false-negative cultures. The increased agreement of NDM identification from poor to fair with repeated sampling along with their poor agreement in the single samples, with and without false-negatives, affirms the complications of NDM identification and supports the recommendation that serial samples help confirm the diagnosis of NDM infections.
Patients with diabetic neuropathy are subject to ulcerations that may be complicated by infection and gangrene, with subsequent risk of amputation. It is the job of the foot specialist to identify and manage these problems early to avoid the unfortunate complication of amputation regardless of the presenting condition of the patient’s limb. We shed light on the hypothesis that suggests that infection and gangrene in a diabetic patient aggravate the degree of ischemia (microvascular, macrovascular, or both) already present enough to endanger the viability of the surrounding tissues unless urgent drainage with decompression and debridement of the necrotic sloughs is performed, with consequent reduction of tissue pressure and improvement in circulation to the area. We present cases with severe infections leading to gangrene and ischemia, which were improved following surgical management with consequent improvement in tissue viability. In these cases, we demonstrate that immediate treatment of the wound despite the delayed presentation of the patients resulted in limb salvage with much less soft-tissue loss than expected before treatment. (J Am Podiatr Med Assoc 99(5): 454–458, 2009)
Diabetic foot infections are a common and often serious problem, accounting for more hospital bed days than any other complication of diabetes. Despite advances in antibiotic drug therapy and surgical management, these infections continue to be a major risk factor for amputations of the lower extremity. Although a variety of wound size and depth classification systems have been adapted for use in codifying diabetic foot ulcerations, none are specific to infection. In 2003, the International Working Group on the Diabetic Foot developed guidelines for managing diabetic foot infections, including the first severity scale specific to these infections. The following year, the Infectious Diseases Society of America published their diabetic foot infection guidelines. Herein, we review some of the critical points from the Executive Summary of the Infectious Diseases Society of America document and provide a commentary following each issue to update the reader on any pertinent changes that have occurred since publication of the original document in 2004.
The importance of a multidisciplinary limb salvage team, apropos of this special issue jointly published by the American Podiatric Medical Association and the Society for Vascular Surgery, cannot be overstated. (J Am Podiatr Med Assoc 100(5): 395–400, 2010)
Antibiotic Tissue Penetration in Diabetic Foot Infections
A Review of the Microdialysis Literature and Needs for Future Research
Although many antimicrobial agents display good in vitro activity against the pathogens frequently implicated in diabetic foot infections, effective treatment can be complicated by reduced tissue penetration in this population secondary to peripheral arterial disease and emerging antimicrobial resistance, which can result in clinical failure. Improved characterization of antibiotic tissue pharmacokinetics and penetration ratios in diabetic foot infections is needed. Microdialysis offers advantages over the skin blister and tissue homogenate studies historically used to define antibiotic penetration in skin and soft-tissue infections by defining antibiotic penetration into the interstitial fluid over the entire concentration versus time profile. However, only a select number of agents currently recommended for treating diabetic foot infections have been evaluated using these methods, which are described herein. Better characterization of the tissue penetration of antibiotic agents is needed for the development of methods for maximizing the pharmacodynamic profile of these agents to ultimately improve treatment outcomes for patients with diabetic foot infections.
Excisional toenail matrixectomies are performed on the area of the foot that has been reported to have the highest concentration of resident microorganisms. A retrospective infection audit was performed to identify whether this unique area of the foot was more susceptible to postoperative infection.
A retrospective audit reviewing the postoperative infection rate over a 6-year period after excisional nail matrixectomy in 111 patients was undertaken.
The postoperative infection rate was found to be high (18.9%) relative to that of clean orthopedic foot and ankle surgery (0.5%–6.5%).
The unique concentration of resident microbes found in the nail folds could help explain the high rate of postoperative infections identified in this study. This may provide some argument to classify excisional nail matrixectomy as clean-contaminated surgery and, thus, warrant routine antibiotic prophylaxis. Further research is recommended to confirm the results of this study and to determine whether appropriately timed oral antibiotic prophylaxis will reduce the infection rate after nail surgery. (J Am Podiatr Med Assoc 101(4): 316–322, 2011)
Lower-Extremity Infections Caused by Serratia marcescens
A Report of Three Cases and a Literature Review
Serratia marcescens is a ubiquitous, facultatively anaerobic, gram-negative bacillus that has been cited to cause infection in immunocompromised populations. In the literature, S marcescens infections of the lower extremity have presented as granulomatous ulceration, abscess, bullous cellulitis, and necrotizing fasciitis. Herein we present a series of three cases of lower-extremity infections in which S marcescens was the sole or a contributing pathogen. We discuss the commonalities of these three cases as well as with those previously cited. All three patients presented with some combination of a similar set of clinical characteristics, including bullae formation, liquefactive necrosis, and black necrotic eschar. All three patients were diabetic and had peripheral vascular disease.
Therapeutic Options for Diabetic Foot Infections
A Review with an Emphasis on Tissue Penetration Characteristics
Foot complications are common in diabetic patients; foot ulcers are among the more serious consequences. These ulcers frequently become infected, and if not treated promptly and appropriately, diabetic foot infections can lead to septic gangrene and amputation. Foot infections may be classified as mild, moderate, or severe; this largely determines the approach to therapy. Staphylococcus aureus is the most common pathogen in these infections, and the increasing incidence of methicillin-resistant S aureus during the past two decades has further complicated antibiotic treatment. Chronic infections are often polymicrobial. Physiologic changes, and local and systemic inflammation, can affect the plasma and tissue pharmacokinetics of antimicrobial agents in diabetic patients, leading to impaired target-site penetration. Knowledge of the serum and tissue concentrations of antibiotics in diabetic patients is, therefore, important for choosing the optimal drug and dose. This article reviews the commonly used therapeutic options for treatment, including many newer antibiotics developed to target multidrug-resistant gram-positive bacteria, and includes available data relating specifically to the tissue penetration of these agents. (J Am Podiatr Med Assoc 100(1): 52–63, 2010)
The elderly make more frequent use of general podiatric medical services than the younger population. It is therefore important for podiatric physicians to become familiar with the general principles of infectious disease as applied to an elderly population, which is susceptible to a wider spectrum of disease with more subtle and unusual clinical signs and symptoms. This article reviews the diagnosis and evaluation of suspected infection, appropriate laboratory testing, patterns of specific infectious disease syndromes, and antibiotic use in the elderly. (J Am Podiatr Med Assoc 94(2): 126-134, 2004)
Osteolysis, caused by active resorption of bone matrix by osteoclasts, can be primary or can develop secondary to a variety of disease processes. An elevated level of inflammatory cytokines in the local milieu and increased blood flow secondary to infection or autonomic neuropathy stimulate the osteoclasts and cause bone loss in the diabetic foot. Charcot's neuroarthropathy and osteomyelitis are well-known foot complications of diabetes, and secondary osteolysis has largely been underappreciated and, hence, underreported. Plain radiographs, an initial component in the evaluation of the diabetic foot, may not successfully differentiate secondary osteolysis from osteomyelitis. We describe a patient with phalangeal osteolysis secondary to soft-tissue infection in whom a correct and timely diagnosis helped avoid unnecessary surgical interventions.