Validation of a Clinical Decision Rule for Ultrasound Identification of MRSA Skin Abscesses in Children.

OBJECTIVE: The aim of this study was to validate an adult-derived clinical decision rule for ultrasound identification of methicillin-resistant Staphylococcus aureus (MRSA) skin abscesses in a pediatric cohort. METHODS: We conducted a retrospective study of skin and soft tissue infections in patients <21 years presenting to the emergency department who had radiology performed ultrasounds completed and wound cultures obtained. Ultrasound scans were reviewed for edge definition, volume, and shape by 2 pediatric emergency physicians with expertise in point-of-care ultrasound, with approximately 25% of scans reviewed by both experts to evaluate interrater reliability. A third, blinded expert weighed in for discrepancies before analysis. Test performance characteristics were calculated for the clinical decision rule in children. RESULTS: Two hundred nine patients were enrolled, with mean age of 9.8 (±6.7) years; 87 (42%) were male. Sixty-nine (33%) patients had a wound culture positive for MRSA. The clinical decision rule had a sensitivity of 86% (95% confidence interval [CI], 75%-93%), specificity of 32% (95% CI, 25%-41%), positive predictive value of 38% (95% CI, 35%-42%), negative predictive value of 82% (95% CI, 71%-89%), positive likelihood ratio of 1.26 (95% CI, 1.08-1.46), negative likelihood ratio of 0.45 (95% CI, 0.24-0.84), and an odds ratio of 2.8 (95% CI, 1.31-5.97). CONCLUSIONS: This clinical decision rule for ultrasound identification of MRSA abscesses had moderately high sensitivity and negative predictive value in pediatric patients, with similar sensitivity compared with the original adult validation group. Ultrasound may help identify MRSA abscesses, allowing for improved antibiotic choices and outcomes for children with MRSA abscesses.

Photonic Hydrogels for Synergistic Visual Bacterial Detection and On-Site Photothermal Disinfection.

Rapid and sensitive diagnostics in the early stage of bacterial infection and immediate treatment play critical roles in the control of infectious diseases. However, it remains challenging to develop integrated systems with both rapid detection of bacterial infection and timely on-demand disinfection ability. Herein, we demonstrate a photonic hydrogel platform integrating visual diagnosis and on-site photothermal disinfection by incorporating Fe3O4@C nanoparticles into a poly(hydroxyethyl methacrylate)-co-polyacrylamide (PHEMA-co-PAAm) matrix. In vitro experiments demonstrate that such a hydrogel can respond to pH variation caused by bacterial metabolism and generate the corresponding color changes to realize naked-eye observation. Meanwhile, its excellent photothermal conversion ability enables it to effectively kill bacteria by destroying cell membranes under near-infrared irradiation. Moreover, the pigskin infection wound model also verifies the bacterial detection performance and disinfection ability of the hydrogel in vivo. Our strategy demonstrates a new approach for visual diagnosis and treatment of bacterial infections.

Sonographically Occult Abscesses of the Buttock and Perineum in Children.

BACKGROUND: Ultrasound (US) is used to differentiate abscess from cellulitis. At our institution, we observed children who had purulent fluid obtained after a negative abscess US. We sought to determine the incidence of sonographically occult abscess (SOA) of the buttock and perineum, and identify associated clinical and demographic characteristics. METHODS: Retrospective chart review including children younger than 18 years old presenting to pediatric emergency department with soft tissue infection of the buttock or perineum and diagnostic radiology US read as negative for abscess. We defined SOA as wound culture growing pathogenic organism obtained within 48 hours of the US. Clinical and demographic characteristics included age, sex, race, ethnicity, fever, history of spontaneous drainage, duration of symptoms, previous methicillin resistant Staphylococcus aureus (MRSA) infection, or previous abscess. We used univariate and multivariate logistic regression to assess correlation between these characteristics and SOA. RESULTS: A total of 217 children were included. Sixty-one (28%) children had SOA; 33 of 61 (54%) had incision and drainage within 4 hours of the US. Of children with SOA, 49 (80%) grew MRSA and 12 (20%) grew methicillin-sensitive S. aureus. In univariate analysis, a history of MRSA, symptom duration 4 days or less, age of younger than 4 years, and Hispanic ethnicity increased the odds of having SOA. In multivariate analysis, history of MRSA and duration of 4 days or less were associated with SOA. CONCLUSIONS: Twenty-eight percent of children in our institution with US of the buttock and perineum negative for abscess had clinical abscess within 48 hours, most within 4 hours. History of MRSA and shorter symptom duration increased the odds of SOA.

An enzyme-responsive and photoactivatable carbon-monoxide releasing molecule for bacterial infection theranostics.

Infections caused by pathogenic bacteria, especially the drug-resistant bacteria, are posing a devastating threat to public health, which underscores the urgent needs for advanced strategies to effectively prevent and treat these intractable issues. Here we report a feasible and effective theranostic platform based on an enzyme-sensitive and photoactivatable carbon monoxide releasing molecule (CORM-Ac) for the successive detection and elimination of bacterial infection. The extracellular bacterial lipase can trigger the excited state intramolecular proton transfer (ESIPT) via elimination of the ester group in CORM-Ac, thus providing a fluorescence switch for an early warning of infection. Subsequently, the potent bactericidal therapy against the model bacterial strains, Staphylococcus aureus (S. aureus) and notorious methicillin-resistant Staphylococcus aureus (MRSA), was readily realized via photoinduced release of CO. In addition, the CORM-Ac and CORM showed good biocompatibility within a wide range of concentrations. The results of an infected animal wound test also demonstrated that the CORM-Ac-loaded gauze was effective in indicating the wound infection and accelerating the wound healing via the photoinduced CO release. The simplicity, functional integration, good biocompatibility and broad adaptability make CORM-Ac very attractive for bacterial theranostic applications.

Efficacy of an imaging device at identifying the presence of bacteria in wounds at a plastic surgery outpatients clinic.

OBJECTIVE: Current standard diagnostic practice of bacterial infections by visual inspection under white light is subjective, and microbiological sampling is suboptimal due to high false negative rates and the lengthy time needed for culture results to arrive. The MolecuLight i:X Imaging Device attempts to combat the issues faced in standard practice by providing a non-contact, real-time method of visualising bacteria within wounds. Our aim was to test this imaging device in a series of patients. METHOD: A single-centre prospective observational study was conducted in the Queen Elizabeth Hospital, Birmingham. During Plastic Surgery Outpatient dressings clinics, patients had their wounds photographed with the imaging device under white light and violet light illumination. Microbiological swabs were obtained of all the wounds. Any clinical signs and symptoms of infection were noted. White light and violet light photographs were compared with correlate visible clinical signs and symptoms with auto-fluorescence images. Auto-fluorescence images were then compared with the microbiological swab results to discern any differences. RESULTS: There were 14 patients with seventeen separate wounds imaged. Of the 17, eight wounds were positive for bacterial growth on microbiological culture. All eight of these were detected positive for bacteria according to auto-fluorescence imaging. There was one wound was detected positive for bacteria by auto-fluorescence imaging with negative microbiological results. CONCLUSION: This study demonstrated the potential benefit of the imaging device due to the correlation between microbiological test results and auto-fluorescence imaging. The device greatly reduces the time taken waiting for results and it is simple, quick to use and non-contact. There is potential for the imaging device to guide swab sampling and aid health professionals in the diagnosis and management of wound infections.

Noninvasive optical and nuclear imaging of Staphylococcus-specific infection with a human monoclonal antibody-based probe.

Staphylococcus aureus infections are a major threat in healthcare, requiring adequate early-stage diagnosis and treatment. This calls for novel diagnostic tools that allow noninvasive in vivo detection of staphylococci. Here we performed a preclinical study to investigate a novel fully-human monoclonal antibody 1D9 that specifically targets the immunodominant staphylococcal antigen A (IsaA). We show that 1D9 binds invariantly to S. aureus cells and may further target other staphylococcal species. Importantly, using a human post-mortem implant model and an in vivo murine skin infection model, preclinical feasibility was demonstrated for 1D9 labeled with the near-infrared fluorophore IRDye800CW to be applied for direct optical imaging of in vivo S. aureus infections. Additionally, 89Zirconium-labeled 1D9 could be used for positron emission tomography imaging of an in vivo S. aureus thigh infection model. Our findings pave the way towards clinical implementation of targeted imaging of staphylococcal infections using the human monoclonal antibody 1D9.

Bacterial biofilm in chronic lesions of hidradenitis suppurativa.

BACKGROUND: Chronic nonhealing or recurrent inflammatory lesions, reminiscent of infection but recalcitrant to antibiotic therapy, generally characterize biofilm-driven diseases. Chronic lesions of hidradenitis suppurativa (HS) exhibit several characteristics, which are compatible with well-known biofilm infections. OBJECTIVES: To determine and quantify the potential presence of bacterial aggregates in chronic HS lesions. METHODS: In 42 consecutive patients with HS suffering from chronic lesions, biopsies were obtained from lesional as well as from perilesional skin. Samples were investigated using peptide nucleic acid-fluorescence in situ hybridization in combination with confocal laser scanning microscopy. In addition, corresponding histopathological analysis on haematoxylin and eosin slides was performed. RESULTS: Biofilms were seen in 67% of the samples of chronic lesions and in 75% of the perilesional samples. The mean diameter of aggregates in lesional skin was significantly greater than in perilesional skin (P = 0·01). Large biofilms (aggregates > 50 µm in diameter) were found in 42% of lesional samples and in only 5% of the perilesional samples (P = 0·009). The majority of the large biofilms were situated in sinus tracts (63%) or in the infundibulum (37%). The majority of the sinus tract samples (73%) contained active bacterial cells, which were associated with inflammation. CONCLUSIONS: This study suggests that biofilm formation is associated with inflammation of chronic HS lesions. The aggregates most likely occur as a secondary event, possibly due to predisposing local anatomical changes such as sinus tracts (tunnels), keratinous detritus and dilated hair follicles.

The Massachusetts abscess rule: a clinical decision rule using ultrasound to identify methicillin-resistant Staphylococcus aureus in skin abscesses.

OBJECTIVES: Treatment failure rates for incision and drainage (I&D) of skin abscesses have increased in recent years and may be attributable to an increased prevalence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). Previous authors have described sonographic features of abscesses, such as the presence of interstitial fluid, characteristics of abscess debris, and depth of abscess cavity. It is possible that the sonographic features are associated with MRSA and can be used to predict the presence of MRSA. The authors describe a potential clinical decision rule (CDR) using sonographic images to predict the presence of CA-MRSA. METHODS: This was a pilot CDR derivation study using databases from two emergency departments (EDs) of patients presenting to the ED with uncomplicated skin abscesses who underwent I&D and culture of the abscess contents. Patients underwent ultrasound (US) imaging of the abscesses prior to I&D. Abscess contents were sent for culture and sensitivity. Two independent physicians experienced in soft tissue US blinded to the culture results and clinical data reviewed the images in a standardized fashion for the presence or absence of the predetermined image characteristics. In the instance of a disagreement between the initial two investigators, a third reviewer adjudicated the findings prior to analysis. The association between the primary outcome (presence of MRSA) and each sonographic feature was assessed using univariate and multivariate analysis. The reliability of each sonographic feature was measured by calculating the kappa (κ) coefficient of interobserver agreement. The decision tree model for the CDR was created with recursive partitioning using variables that were both reliable and strongly associated with MRSA. RESULTS: Of the total of 2,167 patients who presented with skin and soft tissue infections during the study period, 605 patients met inclusion criteria with US imaging and culture and sensitivity of purulence. Among the pathogenic organisms, MRSA was the most frequently isolated, representing 50.1% of all patients. Six of the sonographic features were associated with the presence of MRSA, but only four of these features were reliable using the kappa analysis. Recursive partitioning identified three independent variables that were both associated with MRSA and reliable: 1) the lack of a well-defined edge, 2) small volume, and 3) irregular or indistinct shape. This decision rule demonstrates a sensitivity of 89.2% (95% confidence interval [CI] = 84.7% to 92.7%), a specificity of 44.7% (95% CI = 40.9% to 47.8%), a positive predictive value of 57.9 (95% CI = 55.0 to 60.2), a negative predictive value of 82.9 (95% CI = 75.9 to 88.5), and an odds ratio (OR) of 7.0 (95% CI = 4.0 to 12.2). CONCLUSIONS: According to our putative CDR, patients with skin abscesses that are small, irregularly shaped, or indistinct, with ill-defined edges, are seven times more likely to demonstrate MRSA on culture.

Abscess volume and ultrasound characteristics of community-associated methicillin-resistant Staphylococcus aureus infection.

BACKGROUND: Skin abscesses may vary in volume and inflammation based on organism, although this has not been evaluated using emergency ultrasonography (EUS). OBJECTIVE: The objective of this study was to examine the utility of EUS in discerning skin abscess volume and inflammation by infecting organism. METHODS: This was a secondary analysis of prospectively enrolled subjects 2 months to 19 years presenting for a skin abscess. Subjects with a prior drainage procedure, multiple lesions, incomplete EUS measurements, or lack of an abscess culture were excluded. Abscess cavity dimensions in the x, y, and z planes and signs of local inflammation (cobblestoning, hyperechoic, or thickened dermis) were determined. Abscess volume was calculated using the ellipsoid formula: 4/3 π · (rx) · (ry) · (rz). RESULTS: One hundred eighty-eight subjects met the inclusion criteria. Mean age was 7.7 ± 6.2 years; 39.9% were male. The gluteal region was most commonly involved (33.0%), and lesions were present for a mean 4.2 days (95% confidence interval [CI], 3.8-4.6 days). Methicillin-resistant Staphylococcus aureus (MRSA) was isolated from 125 (66.5%); methicillin-sensitive S. aureus (21.8%) was most common among non-MRSA lesions. Abscess volume was smaller in MRSA (1.12 cm3) compared with non-MRSA (2.46 cm3) lesions (mean difference, -1.33 cm; 95% CI, -2.21 to -0.47 cm3). No differences between MRSA and non-MRSA lesions were present for EUS signs of inflammation. When adjusting for age, duration of lesion, and spontaneous drainage, smaller abscess volumes were associated with MRSA infection (odds ratio, 0.83; 95% CI, 0.71-0.97). Using an optimal threshold value of 1.32 cm3, sensitivity and specificity for non-MRSA lesion were 50.8% and 81.5%, respectively. CONCLUSIONS: Methicillin-resistant S. aureus infection is statistically negatively associated with abscess volume, although of limited predictive ability. Findings using EUS suggest that MRSA does not differ from other organisms with respect to size and inflammation. Clinicians should not consider unique treatment for the presence of MRSA abscess based on these EUS findings.