Tissue versus Swab Culturing of Infected Diabetic Foot Wounds

NewsBot · Apr 29, 2016

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A Comparison of Tissue versus Swab Culturing of Infected Diabetic Foot Wounds.
Huang Y et al
Int J Endocrinol. 2016;2016:8198714. doi: 10.1155/2016/819871

Objective. To compare the efficacy of swabbing versus tissue biopsy for microbiological diagnosis of diabetic foot infection. Methods. This was a prospective trial. Fifty-six patients with diabetic foot infection were divided into the following 3 groups according to the PEDIS grading system: grade 2 (n = 10), grade 3 (n = 29), and grade 4 (n = 17). Two specimens were collected from each wound for microbial culturing after debridement, including a superficial swab and a deep tissue punch biopsy specimen. Results. Swab culturing identified all of the microorganisms isolated from the corresponding deep tissue specimens in 9/10 of grade 2 wounds (90.0%), and this proportion decreased to 12/29 (41.4%) and 7/17 (41.2%) for grades 3 and 4 wounds, respectively (p = 0.02). Moreover, the sensitivity for identifying Gram-negative bacteria, such as E. coli and Citrobacter, by swabbing was low (33.3%). In addition, some Gram-negative bacteria, such as Serratia and Ralstonia pickettii, were isolated from deep tissues but not from swabs. Conclusions. Swab culturing may be reliable for identification of pathogens in diabetic foot wounds classified as grade 2. However, it is advisable to culture deep tissue specimens for wounds of grade ≥3 because swab culturing is associated with a high risk of missing pathogens, especially Gram-negative bacteria.
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Admin2 · Apr 29, 2016

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Diabetic Foot Infections: A Need for Innovative Assessments

NewsBot · Jul 2, 2016

DIABETIC FOOT INFECTIONS: DEEP TISSUE BIOPSIES VERSUS SUPERFICIAL SWABS
N. Howard, S. Brookes Fazakerley, J. Widnall, D. Harvey, S. Platt, G. Jackson
Bone & Joint Surgery; 27 June 2016

We aim to demonstrate the value of deep tissue biopsies to guide antimicrobial treatment of diabetic ulcers. Some recent studies have advocated the role of superficial swabs to guide antibiotic treatment in comparison to deep tissue biopsies previously perceived as the gold standard of microbiology diagnosis. We performed a retrospective analysis of microbiology culture results of patients with infected diabetic ulcers comparing superficial versus deep biopsy microbiology results.

Forty-one diabetic ulcers in 41 patients were included. The mean numbers of isolates from soft tissue and bone biopsies were 2.1 and 1.8 respectively. 39/41 combined soft tissue and bone biopsies were culture positive. The most prevalent organism seen in deep samples was Staphylococcus aureus (14) followed by anaerobes (9), and enterococcus (9). In superficial swab cultures 21 patients (51%) cultured non-specific, mixed skin flora and enteric species. The remaining 20 patients cultured Staphylococcus aureus (11), Streptococcus (6), Pseudomonas (2) and anaerobes (6).

Three superficial swabs matched deep tissue biopsy cultures. 16 deep biopsies grew organisms seen none specifically in superficial swab cultures with 22 deep tissue biopsies cultures growing organisms not seen on superficial swab with 8 being anaerobes.

We have shown that in 54% of cases, deep tissue cultures isolated organisms that were not grown by superficial swab cultures. We highlight the importance of deep tissue biopsies to guide effective treatment.
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NewsBot · Nov 10, 2016

Concordance in diabetic foot ulceration: a cross-sectional study of agreement between wound swabbing and tissue sampling in infected ulcers.
Nelson EA et al
Health Technol Assess. 2016 Nov;20(82):1-176.

BACKGROUND:
There is inadequate evidence to advise clinicians on the relative merits of swabbing versus tissue sampling of infected diabetic foot ulcers (DFUs).
OBJECTIVES:
To determine (1) concordance between culture results from wound swabs and tissue samples from the same ulcer; (2) whether or not differences in bacterial profiles from swabs and tissue samples are clinically relevant; (3) concordance between results from conventional culture versus polymerase chain reaction (PCR); and (4) prognosis for patients with an infected DFU at 12 months' follow-up.
METHODS:
This was a cross-sectional, multicentre study involving patients with diabetes and a foot ulcer that was deemed to be infected by their clinician. Microbiology specimens for culture were taken contemporaneously by swab and by tissue sampling from the same wound. In a substudy, specimens were also processed by PCR. A virtual 'blinded' clinical review compared the appropriateness of patients' initial antibiotic regimens based on the results of swab and tissue specimens. Patients' case notes were reviewed at 12 months to assess prognosis.
RESULTS:
The main study recruited 400 patients, with 247 patients in the clinical review. There were 12 patients in the PCR study and 299 patients in the prognosis study. Patients' median age was 63 years (range 26-99 years), their diabetes duration was 15 years (range 2 weeks-57 years), and their index ulcer duration was 1.8 months (range 3 days-12 years). Half of the ulcers were neuropathic and the remainder were ischaemic/neuroischaemic. Tissue results reported more than one pathogen in significantly more specimens than swabs {86.1% vs. 70.1% of patients, 15.9% difference [95% confidence interval (CI) 11.8% to 20.1%], McNemar's p-value < 0.0001}. The two sampling techniques reported a difference in the identity of pathogens for 58% of patients. The number of pathogens differed in 50.4% of patients. In the clinical review study, clinicians agreed on the need for a change in therapy for 73.3% of patients (considering swab and tissue results separately), but significantly more tissue than swab samples required a change in therapy. Compared with traditional culture, the PCR technique reported additional pathogens for both swab and tissue samples in six (50%) patients and reported the same pathogens in four (33.3%) patients and different pathogens in two (16.7%) patients. The estimated healing rate was 44.5% (95% CI 38.9% to 50.1%). At 12 months post sampling, 45 (15.1%) patients had died, 52 (17.4%) patients had a lower-extremity ipsilateral amputation and 18 (6.0%) patients had revascularisation surgery.
LIMITATIONS:
We did not investigate the potential impact of microbiological information on care. We cannot determine if the improved information yield from tissue sampling is attributable to sample collection, sample handling, processing or reporting.
CONCLUSIONS:
Tissue sampling reported both more pathogens and more organisms overall than swabbing. Both techniques missed some organisms, with tissue sampling missing fewer than swabbing. Results from tissue sampling more frequently led to a (virtual) recommended change in therapy. Long-term prognosis for patients with an infected foot ulcer was poor.
FUTURE WORK:
Research is needed to determine the effect of sampling/processing techniques on clinical outcomes and antibiotic stewardship.
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NewsBot · Jan 9, 2024

To swab or not to swab? A qualitative study of pathology testing, interpretation, and value in diabetes-related foot ulceration
Jennifer Broom et al
Infect Dis Health. 2023 Nov 27:S2468-0451(23)00109-8

Background: Diagnostic testing has been proposed as a key strategy to tackle escalating antimicrobial resistance (AMR). However, effectiveness of testing is limited by the complexities of the hospital environment, including human factors.

Objectives: To examine swab-testing in diabetes-related foot infections as a case study of the factors impacting microbiology testing use, efficacy, and antimicrobial resistance.

Methods: Seventeen clinicians involved in the management of diabetes-related foot infections, including podiatrists, nurses, and doctors, participated in in-depth individual interviews conducted by a qualitative researcher on the investigation and management of diabetes-related foot infections. Thematic analysis was performed.

Results: The multilayered and evolving features of the human-diagnostic interface were described by participants as potential barriers to effective swab-testing in clinical care, including diagnostic training and interpretation deficits; communication difficulties; interpretation deficits and diagnostic assumptions; the influence of inter-professional dynamics; and flow-on consequences for patient decisions and care.

Conclusions: Swab-testing has been used for over 100 years, and yet there remain substantial factors that limit their effective use in clinical practice as demonstrated by this study. A focus on upscaling diagnostic testing, particularly with escalating AMR, without considering complex implementation and human factors is likely to have limited impact on practice improvement. This study identified vulnerability points in the human-diagnostic interaction which should be considered in the implementation of other microbiological tests. This study on the simple wound swab has implications for future diagnostic upscaling and investment, including its role in address antimicrobial resistance.
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