Staphylococcus aureus is the most common identified cause of cellulitis: a systematic review

Toward an Objective Diagnostic Test for Bacterial Cellulitis

Background

Prior studies repeatedly showed that cultures of skin lesions diagnosed as "cellulitis" are usually negative. However, lack of a gold standard for diagnosis (against which culture might be judged) and failure to assess the human immune response are important limitations of prior work. In this pilot study, we aimed to develop a criterion standard for research on bacterial cellulitis, to evaluate the sensitivity of procalcitonin for bacterial cellulitis, and to use gene expression analysis to find other candidate diagnostic markers.

Methods

We classified lesions via biopsies, 16s rRNA gene detection, culture, and histopathology. We quantified procalcitonin expression in blood. We also used Nanostring technology to quantify transcription of immunomodulators that may distinguish cases from inflamed controls.

Results

Of 28 participants, 15 had a clinical diagnosis of cellulitis, six had a diagnosis of non-infectious dermatitis, and seven were normal volunteers. Of the “cellulitis” patients, three (20%) had pathogens isolated, and were designated confirmed cases. Procalcitonin was undetectable in all three. HLA-DQA1 was expressed 34-fold more in confirmed cases vs. controls (fold change of geometric mean). Heat maps depicting multiplex gene expression analysis revealed a distinct profile of gene expression in confirmed cases relative to comparators.

Conclusions

Most “cellulitis” patients had microbiologically-negative biopsies. Procalcitonin was undetectable, and HLA-DQA1 elevated, in confirmed bacterial cases. Multivariable transcriptomic profiling results supported our algorithm’s ability to identify patients with true bacterial cellulitis. A larger sample may allow discovery of an immunological signature capable of distinguishing bacterial cellulitis from its mimics in clinical practice.

Antimicrobial Activities of Ceftaroline and Comparator Agents against Bacterial Organisms Causing Bacteremia in Patients with Skin and Skin Structure Infections in U.S. Medical Centers, 2008 to 2014

We evaluated the antimicrobial susceptibility of 1,454 organisms consecutively collected from patients with bacteremia associated with skin and skin structure infections. The most common organisms obtained wereStaphylococcus aureus(670 organisms [46.1%]),Escherichia coli(200 organisms [13.8%]), β-hemolytic streptococci (βHS) (138 organisms [9.5%]), andKlebsiella pneumoniae(109 organisms [7.5%]). The susceptibility rates for ceftaroline were 97.9% forS. aureus(95.9% among methicillin-resistantS. aureus[MRSA]), 100.0% for βHS, 86.5% forE. coli, and 89.0% forK. pneumoniae Ceftaroline and tigecycline provided the best overall coverage.

Etiology of Cellulitis and Clinical Prediction of Streptococcal Disease: A Prospective Study

Background.  The importance of bacteria other than group A streptococci (GAS) in different clinical presentations of cellulitis is unclear, commonly leading to treatment with broad-spectrum antibiotics. The aim of this study was to describe the etiological and clinical spectrum of cellulitis and identify clinical features predicting streptococcal etiology. Methods.  We prospectively enrolled 216 patients hospitalized with cellulitis. Clinical details were registered. Bacterial culture was performed from blood, cutaneous or subcutaneous tissue, and/or swabs from skin lesions. Paired serum samples were analyzed for anti-streptolysin O and anti-deoxyribonuclease B antibodies. Results.  Serology or blood or tissue culture confirmed β-hemolytic streptococcal (BHS) etiology in 72% (146 of 203) of cases. An additional 13% (27 of 203) of cases had probable BHS infection, indicated by penicillin response or BHS cultured from skin swabs. β-hemolytic streptococcal etiology was predominant in all clinical subgroups, including patients without sharply demarcated erythema. β-hemolytic group C or G streptococci (GCS/GGS) were more commonly isolated than GAS (36 vs 22 cases). This predominance was found in the lower extremity infections. Group C or G streptococci in swabs were associated with seropositivity just as often as GAS. Staphylococcus aureus was cultured from swabs as a single pathogen in 24 cases, 14 (64%) of which had confirmed BHS etiology. Individual BHS-associated clinical characteristics increased the likelihood of confirmed BHS disease only slightly; positive likelihood ratios did not exceed 2.1. Conclusions.  β-hemolytic streptococci were the dominating cause of cellulitis in all clinical subgroups and among cases with S aureus in cutaneous swabs. Group C or G streptococci were more frequently detected than GAS. No single clinical feature substantially increased the probability of confirmed BHS etiology.

Blood Cultures Are Not Useful in the Evaluation of Children with Uncomplicated Superficial Skin and Soft Tissue Infections

BACKGROUND

Blood cultures (BCs) are commonly performed on children admitted to hospital for skin and soft tissue infections (SSTIs). In recent years, this practice has been questioned in patients with uncomplicated SSTIs because of its low yield. At the same time, however, an increase in community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections has been described; its influence on rates of bacteremia in patients with SSTIs is unclear. The aims of the study were to describe the performance and the yield of BC in immunocompetent patients with uncomplicated SSTIs and to determine the prevalence of CA-MRSA as a causative agent in our area.

METHODS

Retrospective study: immunocompetent patients younger than 18 years evaluated in the emergency department and admitted for uncomplicated SSTIs (cellulitis, abscess, impetigo or erysipelas) from July 1, 2010 to June 31, 2014 were included. Patients referred from other hospitals who were receiving parenteral antibiotics and patients with complicated SSTIs (surgical or traumatic wound infection, need for surgical intervention and infected ulcers or burns) were excluded.

RESULTS

We included 445 cases: 348 (78.2%) cellulitis, 78 (17.5%) abscess and 19 (4.3%) impetigo. BCs were performed on 353 (79.3%) patients. Two (0.6%; 95% confidence interval: 0.2-2.0%) were positive and 10 (2.8%; 95% confidence interval: 1.5-5.1%) contaminated. The positive BCs grew S. aureus and Streptococcus pyogenes. Wound cultures were performed on 148 (33.3%) patients; 98 (66.2%) were positive. In 22 (22.4%) patients CA-MRSA grew, accounting for 14.9% of overall wound cultures.

CONCLUSIONS

BCs are not useful in the management of immunocompetent patients admitted to the hospital with uncomplicated SSTIs. The prevalence of CA-MRSA is low in our area, but continuing careful surveillance is needed.

Clinical and microbiological characteristics of purulent and non-purulent cellulitis in hospitalized Taiwanese adults in the era of community-associated methicillin-resistant Staphylococcus aureus

BACKGROUND

The risk factors, microbial etiology, differentiation, and clinical features of purulent and non-purulent cellulitis are not well defined in Taiwan.

METHODS

We conducted a retrospective cohort study of hospitalized adults with cellulitis in Taiwan in 2013. The demographic characteristics, underlying diseases, clinical manifestations, laboratory and microbiological findings, treatments, and outcomes were compared for patients with purulent and non-purulent cellulitis.

RESULTS

Of the 465 patients, 369 had non-purulent cellulitis and 96 had purulent cellulitis. The non-purulent group was significantly older (p = 0.001) and was more likely to have lower limb involvement (p < 0.001), tinea pedis (p = 0.003), stasis dermatitis (p = 0.025), a higher Charlson comorbidity score (p = 0.03), and recurrence at 6 months post-infection (p = 0.001) than the purulent group. The purulent group was more likely to have a wound (p < 0.001) and a longer hospital stay (p = 0.001) and duration of antimicrobial therapy (p = 0.003) than the non-purulent group. The etiological agent was identified in 35.5 % of the non-purulent cases, with β-hemolytic streptococci the most frequent cause (70.2 %). The etiological agent was identified in 83.3 % of the purulent cases, with Staphylococcus aureus the predominant pathogen (60 %): 50 % of these were methicillin-resistant S. aureus (MRSA). In multivariable analysis, purulent group (odds ratio (OR), 5.188; 95 % confidence interval (CI), 1.995-13.493; p = 0.001) was a positive predictor of MRSA. The prescribed antimicrobial agents were significantly different between the purulent and non-purulent groups, with penicillin the most frequently used antimicrobial agent in the non-purulent group (35.2 %), and oxacillin the most frequent in the purulent group (39.6 %). The appropriate antimicrobial agent was more frequently prescribed in the non-purulent group than in the purulent group (83.2 % vs. 53.8 %, p < 0.001).

CONCLUSIONS

The epidemiology, clinical features, and microbiology of purulent and non-purulent cellulitis were significantly different in hospitalized Taiwanese adults. Purulence was a positive predictor of MRSA as the causal agent of cellulitis. These findings provide added support for the adoption of the IDSA guidelines for empirical antimicrobial therapy of cellulitis in Taiwan.

Inability of polymerase chain reaction, pyrosequencing, and culture of infected and uninfected site skin biopsy specimens to identify the cause of cellulitis

BACKGROUND

The cause of cellulitis is unclear. Streptococcus pyogenes, and to a lesser extent, Staphylococcus aureus, are presumed pathogens.

METHODS

We conducted a study of adults with acute cellulitis without drainage presenting to a US emergency department research network. Skin biopsy specimens were taken from the infected site and a comparable uninfected site on the opposite side of the body. Microbiology was evaluated using quantitative polymerase chain reaction (PCR), pyrosequencing, and standard culture techniques. To determine the cause, the prevalence and quantity of bacterial species at the infected and uninfected sites were compared.

RESULTS

Among 50 subjects with biopsy specimens from infected and uninfected sites, culture rarely identified a bacterium. Among 49 subjects with paired specimens from infected and uninfected sites tested with PCR, methicillin-susceptible S. aureus was identified in 20 (41%) and 17 (34%), respectively. Pyrosequencing identified abundant atypical bacteria in addition to streptococci and staphylococci. Among 49 subjects with paired specimens tested by pyrosequencing, S. aureus was identified from 11 (22%) and 15 (31%) and streptococci from 15 (31%) and 20 (41%) of the specimens, respectively. Methicillin-resistant S. aureus was not found by culture or PCR, and S. pyogenes was not identified by any technique.

CONCLUSIONS

The bacterial cause of cellulitis cannot be determined by comparing the prevalence and quantity of pathogens from infected and uninfected skin biopsy specimens using current molecular techniques. Methicillin-susceptible S. aureus was detected but not methicillin-resistant S. aureus or S. pyogenes from cellulitis tissue specimens. For now, optimal treatment will need to be guided by clinical trials. Noninfectious causes should also be explored.

A glossary of terms to assist the recognition and diagnosis of skin conditions associated with lower-limb chronic oedema

There are a number of recognised skin conditions associated with chronic oedema, but the lack of agreed definitions and terminology often leads to poor recognition and a delay in treatment. Many patients are given a diagnostic 'label' (e.g. varicose eczema) that often turns out to be incorrect, leading to an interruption in the patient pathway. Every skin condition can be described in a variety of ways and each professional group adheres to certain phrases and words that, within each discipline, are recognised, but when making onward referral or working between professions, it helps to have clear and concise definitions. This article aims is to standardise the terminology used to describe skin conditions of the lower limbs among health professionals, removing some of the discrepancy, and to develop a glossary to aid recognition, definition and hence diagnosis to ensure prompt and appropriate management is implemented.

Clindamycin versus trimethoprim-sulfamethoxazole for uncomplicated skin infections

BACKGROUND

Skin and skin-structure infections are common in ambulatory settings. However, the efficacy of various antibiotic regimens in the era of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) is unclear.

METHODS

We enrolled outpatients with uncomplicated skin infections who had cellulitis, abscesses larger than 5 cm in diameter (smaller for younger children), or both. Patients were enrolled at four study sites. All abscesses underwent incision and drainage. Patients were randomly assigned in a 1:1 ratio to receive either clindamycin or trimethoprim-sulfamethoxazole (TMP-SMX) for 10 days. Patients and investigators were unaware of the treatment assignments and microbiologic test results. The primary outcome was clinical cure 7 to 10 days after the end of treatment.

RESULTS

A total of 524 patients were enrolled (264 in the clindamycin group and 260 in the TMP-SMX group), including 155 children (29.6%). One hundred sixty patients (30.5%) had an abscess, 280 (53.4%) had cellulitis, and 82 (15.6%) had mixed infection, defined as at least one abscess lesion and one cellulitis lesion. S. aureus was isolated from the lesions of 217 patients (41.4%); the isolates in 167 (77.0%) of these patients were MRSA. The proportion of patients cured was similar in the two treatment groups in the intention-to-treat population (80.3% in the clindamycin group and 77.7% in the TMP-SMX group; difference, -2.6 percentage points; 95% confidence interval [CI], -10.2 to 4.9; P=0.52) and in the populations of patients who could be evaluated (466 patients; 89.5% in the clindamycin group and 88.2% in the TMP-SMX group; difference, -1.2 percentage points; 95% CI, -7.6 to 5.1; P=0.77). Cure rates did not differ significantly between the two treatments in the subgroups of children, adults, and patients with abscess versus cellulitis. The proportion of patients with adverse events was similar in the two groups.

CONCLUSIONS

We found no significant difference between clindamycin and TMP-SMX, with respect to either efficacy or side-effect profile, for the treatment of uncomplicated skin infections, including both cellulitis and abscesses. (Funded by the National Institute of Allergy and Infectious Diseases and the National Center for Advancing Translational Sciences, National Institutes of Health; ClinicalTrials.gov number, NCT00730028.).

Evidence of streptococcal origin of acute non-necrotising cellulitis: a serological study

Bacteriological diagnosis is rarely achieved in acute cellulitis. Beta-haemolytic streptococci and Staphylococcus aureus are considered the main pathogens. The role of the latter is, however, unclear in cases of non-suppurative cellulitis. We conducted a serological study to investigate the bacterial aetiology of acute non-necrotising cellulitis. Anti-streptolysin O (ASO), anti-deoxyribonuclease B (ADN) and anti-staphylolysin (ASTA) titres were measured from acute and convalescent phase sera of 77 patients hospitalised because of acute bacterial non-necrotising cellulitis and from the serum samples of 89 control subjects matched for age and sex. Antibiotic treatment decisions were also reviewed. Streptococcal serology was positive in 53 (69%) of the 77 cases. Furthermore, ten cases without serological evidence of streptococcal infection were successfully treated with penicillin. Positive ASO and ADN titres were detected in ten (11%) and three (3%) of the 89 controls, respectively, and ASTA was elevated in three patients and 11 controls. Our findings suggest that acute non-necrotising cellulitis without pus formation is mostly of streptococcal origin and that penicillin can be used as the first-line therapy for most patients.

Hospitalist perspective on the treatment of skin and soft tissue infections

The prevalence of skin and soft tissue infections (SSTIs) has been increasing in the United States. These infections are associated with an increase in hospital admissions. Hospitalists play an increasingly important role in the management of these infections and need to use hospital resources efficiently and effectively. When available, observation units are useful for treating low-risk patients who do not require hospital admission. Imaging tools may help to exclude abscesses and necrotizing soft tissue infections; however, surgical exploration remains the principal means of diagnosing necrotizing soft tissue infections. The most common pathogens that cause SSTIs are streptococci and Staphylococcus aureus. Methicillin-resistant S aureus (MRSA) is a prevalent pathogen, and concerns are increasing regarding the unclear distinctions between community-acquired and hospital-acquired MRSA. Other less frequent pathogens that cause SSTIs include Enterococcus species, Escherichia coli, Klebsiella species, Enterobacter species, and Pseudomonas aeruginosa. Cephalexin and clindamycin are suitable options for infections caused by streptococcal species and methicillin-susceptible S aureus. The increasing resistance of S aureus and Streptococcus pyogenes to erythromycin limits its use in these infections, and better alternatives are available. Parenteral cefazolin, nafcillin, or oxacillin can be used in hospitalized patients with nonpurulent cellulitis caused by streptococci and methicillin-susceptible S aureus. When oral MRSA therapy is indicated, clindamycin, doxycycline, trimethoprim-sulfamethoxazole, or linezolid is appropriate. Vancomycin, linezolid, daptomycin, tigecycline, telavancin, and ceftaroline fosamil are intravenous options that should be used in MRSA infections that require patient hospitalization. In the treatment of patients with SSTIs, hospitalists are at the forefront of providing proper patient care that reduces hospital costs, duration of therapy, and therapeutic failures. This review updates guidelines on the management of SSTIs with a focus on infections caused by S aureus, particularly MRSA, and outlines the role of the hospitalist in the effective management of SSTIs.

Comparing short to standard duration of antibiotic therapy for patients hospitalized with cellulitis (DANCE): study protocol for a randomized controlled trial

BACKGROUND

Recommended therapy duration for patients hospitalized with cellulitis is 10-14 days. Unnecessary use of antibiotics is one of the key factors driving resistance. Recent studies have shown that antibiotic therapy for cellulitis in outpatients can safely be shortened, despite residual inflammation. This study will compare in hospitalized patients the safety and effectiveness of shortening antibiotic therapy for cellulitis from 12 to 6 days.

METHODS/DESIGN

In a multicenter, randomized, double-blind, non-inferiority trial, adult patients admitted with cellulitis will be included. Cellulitis is defined as warmth, erythema, and induration of the skin and/or subcutaneous tissue, with or without pain (including erysipelas). All patients will initially be treated with intravenous flucloxacillin, and will be evaluated after 5-6 days. Those who have improved substantially (defined as being afebrile, and having a lower cellulitis severity score) will be randomized at day 6 between additional 6 days of oral flucloxacillin (n = 198) or placebo (n = 198). Treatment success is defined as resolution of cellulitis on day 14 (disappearance of warmth and tenderness, improvement of erythema and edema), without the need of additional antibiotics for cellulitis by day 28. Secondary endpoints are relapse rate (up to day 90), speed of recovery (using a cellulitis severity score until day 28, and VAS scores on pain and swelling until day 90), quality of life (using the SF-36 and EQ-5D questionnaires) and costs (associated with total antibiotic use and health-care resource utilization up to day 90).

DISCUSSION

Inclusion is planned to start in Q2 2014.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT02032654) and the Netherlands Trial Register (NTR4360).

Cutaneous bacterial infections caused by Staphylococcus aureus and Streptococcus pyogenes in infants and children

Acute bacterial skin and skin structure infections (SSSIs) are among the most common bacterial infections in children. The medical burden of SSSIs, particularly abscesses, has increased nationwide since the emergence of community-acquired methicillin-resistant Staphylococcus aureus. SSSIs represent a wide spectrum of disease severity. Prompt recognition, timely institution of appropriate therapy, and judicious antimicrobial use optimize patient outcomes. For abscesses, incision and drainage are paramount and might avoid the need for antibiotic treatment in uncomplicated cases. If indicated, empiric antimicrobial therapy should target Streptococcus pyogenes for nonpurulent SSSIs, such as uncomplicated cellulitis, and S aureus for purulent SSSIs such as abscesses.

Is Community-Acquired Methicillin-Resistant Staphylococcus aureus Coverage Needed for Cellulitis?

Methicillin-resistant Staphylococcus aureus (MRSA) has become the dominant strain of Staphylococcus aureus in many communities of the United States. As a result, many clinicians are now empirically covering for this pathogen in the treatment of various skin and soft-tissue infections. Should this practice apply to cellulitis? In order to answer this question, we defined cellulitis and reviewed the pathogenesis, microbiology, and current studies of inpatient and outpatient antimicrobial therapy. The current evidence suggests empirical MRSA coverage for community-acquired cellulitis may not be necessary in non-purulent (non-suppurative) forms of this infection. Most cases are non-purulent and not amenable to culture although antibody studies indicate streptococci are the most common etiologic agents. Current studies of antimicrobial therapy tend to agree with this finding. Empirical beta-lactam therapy directed primarily at streptococci appears sufficient for non-purulent cellulitis regardless of the prevalence of MRSA in the community.

Oral flucloxacillin and phenoxymethylpenicillin versus flucloxacillin alone for the emergency department outpatient treatment of cellulitis: study protocol for a randomised controlled trial

Background

Oral flucloxacillin, either alone or in combination with phenoxymethylpenicillin, is a commonly prescribed antibiotic for the treatment of cellulitis, particularly in Ireland and the United Kingdom. This study aims to establish the non-inferiority of oral monotherapy (flucloxacillin alone) to dual therapy (flucloxacillin and phenoxymethylpenicillin) for the outpatient treatment of cellulitis in adults.

Methods/design

This study is a multicentre, randomised, double-blind, placebo-controlled trial of adults who present to the emergency department (ED) with cellulitis that is deemed treatable on an outpatient basis with oral antibiotics. After fulfilling specified inclusion and exclusion criteria, informed consent will be taken. Patients will be given a treatment pack containing 7 days of treatment with flucloxacillin 500 mg four times daily and placebo or flucloxacillin 500 mg four times daily and phenoxymethylpenicillin 500 mg four times daily. The primary outcome measure under study is the proportion of patients in each group in which there is greater than or equal to a 50% reduction in the area of diameter of infection from the area measured at enrolment at the end-of-treatment visit (7 to 10 days). Secondary endpoints include a health-related quality of life measurement as rated by the SF-36 score and the Extremity Soft Tissue Infection Score (not validated), compliance and adverse events. Patients will be followed up by telephone call at 3 days, end-of-treatment visit (EOT) at 7 to 10 days and test-of-cure (TOC) visit at 30 days. To achieve 90% power, a sample size of 172 patients per treatment arm is needed. This assumes a treatment success rate of 85% with oral flucloxacillin and phenoxymethylpenicillin, an equivalence threshold Δ = 12.5% and an α = 0.025. Non-inferiority will be assessed using a one-sided confidence interval on the difference of proportions between the two groups. Standard analysis including per-protocol and intention-to-treat will be performed.

Discussion

This trial aims to establish the non-inferiority of flucloxacillin monotherapy to dual therapy in the treatment of uncomplicated cellulitis among ED patients. In doing so, this trial will bridge a knowledge gap in this understudied and common condition and will be relevant to clinicians across several different disciplines.

Trial registration

EudraCT Number 2008-006151-42

Skin and soft tissue infections and associated complications among commercially insured patients aged 0-64 years with and without diabetes in the U.S

Introduction

Skin and soft tissue infections (SSTIs) are common infections occurring in ambulatory and inpatient settings. The extent of complications associated with these infections by diabetes status is not well established.

Methods

Using a very large repository database, we examined medical and pharmacy claims of individuals aged 0–64 between 2005 and 2010 enrolled in U.S. health plans. Diabetes, SSTIs, and SSTI-associated complications were identified by ICD-9 codes. SSTIs were stratified by clinical category and setting of initial diagnosis.

Results

We identified 2,227,401 SSTI episodes, 10% of which occurred in diabetic individuals. Most SSTIs were initially diagnosed in ambulatory settings independent from diabetes status. Abscess/cellulitis was the more common SSTI group in diabetic and non-diabetic individuals (66% and 59%, respectively). There were differences in the frequencies of SSTI categories between diabetic and non-diabetic individuals (p<0.01). Among SSTIs diagnosed in ambulatory settings, the SSTI-associated complication rate was over five times higher in people with diabetes than in people without diabetes (4.9% vs. 0.8%, p<0.01) and SSTI-associated hospitalizations were 4.9% and 1.1% in patients with and without diabetes, respectively. Among SSTIs diagnosed in the inpatient setting, bacteremia/endocarditis/septicemia/sepsis was the most common associated complication occurring in 25% and 16% of SSTIs in patients with and without diabetes, respectively (p<0.01).

Conclusions

Among persons with SSTIs, we found SSTI-associated complications were five times higher and SSTI-associated hospitalizations were four times higher, in patients with diabetes compared to those without diabetes. SSTI prevention efforts in individuals with diabetes may have significant impact on morbidity and healthcare resource utilization.

PCR offers no advantage over culture for microbiologic diagnosis in cellulitis

PURPOSE

Most cases of cellulitis are traditionally attributed to β-hemolytic Streptococcus and Staphylococcus species, although in most cases, no organism is identified. Development of PCR using the conserved bacterial 16 S rRNA DNA permits identification of bacteria independent of conventional culture approaches and prior use of antibiotics.

METHODS

We used PCR-based techniques to identify cellulitis etiology using aspirate samples from affected skin. Saline was infiltrated and aspirated at the site of greatest erythema or at the cellulitic border. Samples were tested for 16 S rRNA DNA, and organism-specific probes used to identify bacteria commonly seen in skin infections.

RESULTS

Aspirates from 32 patients were studied, and 16 S rRNA DNA was detected in nine of these patient samples (28.1%). Bacterial species were identified by PCR methods in six of these nine samples (66.6%), with S. aureus and methicillin-resistant S. aureus (MRSA) identified in four and two, respectively, of these samples. Of the patients with positive aspirate bacterial cultures (3/9, 33.3%), S. aureus and coagulase-negative Staphylococcus (CoNS) were present on cultures of two of the three (both 66.6%) positive samples. Only in one of the three positive bacterial cultures did the PCR method detect the same organism as was detected by culture. Among patients with positive provider-collected clinical cultures, MRSA was the predominant organism (11/18, 61.1%) and when present, it was found as the sole organism. Where S. aureus or Streptococcus species were detected by molecular methods, clinical cultures yielded a positive result as well.

CONCLUSIONS

PCR-based techniques do not appear to be more sensitive than aspirate cultures for the detection of pathogens in cellulitis.

Cellulitis: definition, etiology, and clinical features

Cellulitis is a common condition seen by physicians. Over the past decade, skin and soft tissue infections from community-associated methicillin-resistant Staphylococcus aureus have become increasingly common. In this article, the definition, etiology, and clinical features of cellulitis are reviewed, and the importance of differentiating cellulitis from necrotizing soft tissue infections is emphasized. Empiric antimicrobial recommendations are suggested, including the most recent recommendations from the Infectious Disease Society of America.

A systematic review of bacteremias in cellulitis and erysipelas

OBJECTIVES

Because of the difficulty of obtaining bacterial cultures from patients with cellulitis and erysipelas, the microbiology of these common infections remains incompletely defined. Given the emergence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) over the past decade the proportion of infections due to S. aureus has become particularly relevant.

METHODS

OVID was used to search Medline using the focused subject headings "cellulitis", "erysipelas" and "soft tissue infections". All references that involved adult patients with cellulitis or erysipelas and reported associated bacteremias and specific pathogens were included in the review.

RESULTS

For erysipelas, 4.6% of 607 patients had positive blood cultures, of which 46% were Streptococcus pyogenes, 29% were other β-hemolytic streptococci, 14% were Staphylococcus aureus, and 11% were Gram-negative organisms. For cellulitis, 7.9% of 1578 patients had positive blood cultures of which 19% were Streptococcus pyogenes, 38% were other β-hemolytic streptococci, 14% were Staphylococcus aureus, and 28% were Gram-negative organisms.

CONCLUSIONS

Although the strength of our conclusions are somewhat limited by the heterogeneity of included cases, our results support the traditional view that cellulitis and erysipelas are primarily due to streptococcal species, with a smaller proportion due to S. aureus. Our results also argue against the current distinction between cellulitis and erysipelas in terms of the relative proportion of infections due to S. aureus.

Non-suppurative cellulitis: risk factors and its association with Staphylococcus aureus colonization in an area of endemic community-associated methicillin-resistant S. aureus infections

Suppurative methicillin-resistant Staphylococcus aureus (MRSA) skin infections are common and associated with MRSA colonization, but little is known about non-suppurative cellulitis and its relationship with MRSA colonization in areas endemic for community-associated MRSA. We prospectively enrolled patients hospitalized for non-suppurative cellulitis (n=50) and matched controls (n=100) and found S. aureus colonization was similar in cases and controls (30% vs. 25%, P=0·95). MRSA was uncommon in cases (6%) and controls (3%) (P=0·39). All MRSA isolates were USA300 by pulsed-field gel electrophoresis. Independent risk factors for non-suppurative cellulitis were diabetes (OR 3·5, 95% CI 1·4-8·9, P=0·01) and homelessness in the previous year (OR 6·4, 95% CI 1·9-20·9, P=0·002). These findings suggest that MRSA may only rarely be causative of non-suppurative cellulitis.