Epidemiology and microbiology of cellulitis and bacterial soft tissue infection during HIV disease: a 10-year survey

HIV and skin infections

HIV infection alters the skin microbiome and predisposes to a wide range of cutaneous infections, from atypical presentations of common skin infections to severe disseminated infections involving the skin that are AIDS-defining illnesses. Bacterial infection of the skin, most commonly caused by Staphylococcus aureus, occurs frequently and can result in bacteremia. Nontuberculous mycobacterial infections that are usually localized to the skin may disseminate, and guidance on the treatment of these infections is limited. Herpes simplex can be severe, and less common presentations such as herpetic sycosis and herpes vegetans have been reported. Severe herpes zoster, including disseminated infection, requires intravenous antiviral treatment. Viral warts can be particularly difficult to treat, and in atypical or treatment-resistant cases a biopsy should be considered. Superficial candidosis occurs very commonly in people living with HIV, and antifungal resistance is an increasing problem in non-albicans Candida species. Systemic infections carry a poor prognosis. In tropical settings the endemic mycoses including histoplasmosis are a problem for people living with HIV, and opportunistic infections can affect those with advanced HIV in all parts of the world. Most cutaneous infections can develop or worsen as a result of immune reconstitution in the weeks to months after starting antiretroviral therapy. Direct microscopic examination of clinical material can facilitate rapid diagnosis and treatment initiation, although culture is important to provide microbiological confirmation and guide treatment.

T Cell Immunity and the Quest for Protective Vaccines against Staphylococcus aureus Infection

Staphylococcus aureus is a wide-spread human pathogen, and one of the top causative agents of nosocomial infections. The prevalence of antibiotic-resistant S. aureus strains, which are associated with higher mortality and morbidity rates than antibiotic-susceptible strains, is increasing around the world. Vaccination would be an effective preventive measure against S. aureus infection, but to date, every vaccine developed has failed in clinical trials, despite inducing robust antibody responses. These results suggest that induction of humoral immunity does not suffice to confer protection against the infection. Evidence from studies in murine models and in patients with immune defects support a role of T cell-mediated immunity in protective responses against S. aureus. Here, we review the current understanding of the mechanisms underlying adaptive immunity to S. aureus infections and discuss these findings in light of the recent S. aureus vaccine trial failures. We make the case for the need to develop anti-S. aureus vaccines that can specifically elicit robust and durable protective memory T cell subsets.

Development of a vaccine against Staphylococcus aureus invasive infections: Evidence based on human immunity, genetics and bacterial evasion mechanisms

Invasive Staphylococcus aureus infections are a leading cause of morbidity and mortality in both hospital and community settings, especially with the widespread emergence of virulent and multi-drug resistant methicillin-resistant S. aureus strains. There is an urgent and unmet clinical need for non-antibiotic immune-based approaches to treat these infections as the increasing antibiotic resistance is creating a serious threat to public health. However, all vaccination attempts aimed at preventing S. aureus invasive infections have failed in human trials, especially all vaccines aimed at generating high titers of opsonic antibodies against S. aureus surface antigens to facilitate antibody-mediated bacterial clearance. In this review, we summarize the data from humans regarding the immune responses that protect against invasive S. aureus infections as well as host genetic factors and bacterial evasion mechanisms, which are important to consider for the future development of effective and successful vaccines and immunotherapies against invasive S. aureus infections in humans. The evidence presented form the basis for a hypothesis that staphylococcal toxins (including superantigens and pore-forming toxins) are important virulence factors, and targeting the neutralization of these toxins are more likely to provide a therapeutic benefit in contrast to prior vaccine attempts to generate antibodies to facilitate opsonophagocytosis.

Staphylococcus aureus Epicutaneous Infection Is Suppressed by Lactococcus lactis Strain Plasma via Interleukin 17A Elicitation

BACKGROUND

Lactococcus lactis strain Plasma (LC-Plasma) was revealed to stimulate plasmacytoid dendritic cells and induce antiviral immunity in vitro and in vivo. In this study, we assessed the effects of LC-Plasma on skin immunity.

METHODS

To evaluate the effect of LC-Plasma on skin immunity and Staphylococcus aureus epicutaneous infection, lymphocyte activities in skin-draining lymph nodes (SLNs) and gene expression in skin were analyzed after 2 weeks of oral administration of LC-Plasma. To evaluate the mechanisms of interleukin 17A production, SLN lymphocytes were cultured with or without LC-Plasma, and the interleukin 17A concentrations in supernatants were measured.

RESULTS

Oral administration of LC-Plasma activated plasma dendritic cells in SLNs, augmented skin homeostasis, and elicited suppression of Staphylococcus aureus, Staphylococcus epidermidis, and Propionibacterium acnes proliferation. In addition, significant suppression of the S. aureus burden and reduced skin inflammation were observed following oral administration of LC-Plasma. Furthermore, a subsequent in vitro study revealed that LC-Plasma could elicit interleukin 17A production from CD8+ T cells and that its induction mechanism depended on the Toll-like receptor 9 signaling pathway, with type I interferon partially involved.

CONCLUSIONS

Our results suggest that LC-Plasma oral administration enhances skin homeostasis via plasma dendritic cell activation in SLNs, resulting in suppression of S. aureus epicutaneous infection and skin inflammation.

Immunity to Staphylococcus aureus: Implications for Vaccine Development

Cell-mediated immunity seems to be critical for prevention and resolution of invasive S. aureus infections, but an imbalance in this immunity may also produce SIRS and death or an inadequate protective response with prolonged bacteremia and death. This dysregulation is likely at the heart of mortality and severe disease in humans. Anti-toxin antibodies may also come into play in reducing the severity of S. aureus infections, but these antibodies might also address superantigen-induced immune dysregulation. Thus, while changing intrinsic T cell responses may be therapeutically difficult, monoclonal antibodies against superantigens may have utility in addressing dysfunctional immune responses to S. aureus. The models above are hypotheses for examining, and potentially dramatically improving immune response to and safety of S. aureus vaccines.

Eyelid and Orbital Involvement in HIV Infection - An African Perspective

Both infective and neoplastic eyelid and orbital conditions in human immunodeficiency virus (HIV) infected patients are often the result of opportunistic or co-infections (OI). In most cases, these clinical findings in younger patients alert the physician to suspected underlying HIV infection. When the eyelids and periorbital skin are primarily involved in OI with varicella-zoster virus it is called Herpes Zoster Ophthalmicus. Co-infection with a Pox virus manifests as molluscum contagiosum eruptions. Orbital cellulitis is secondary to various organisms (Mycobacterium tuberculosis, Candida albicans, Aspergillus). Neoplastic disorders are also often associated with OI such as human herpes virus 8 in Kaposi Sarcoma, Epstein-Barr virus in Hodgkin Lymphoma and human papillomavirus 16 and 18 in squamous cell carcinoma. In this review we share our personal clinical experience with HIV disease in Sub-Saharan Africa over more than two decades and provide photographs of cases to illustrate pertinent aspects of the conditions discussed.

Prevalence of skin diseases among hospitals in the public healthcare system of a developing country

BACKGROUND

Skin diseases in the population are universal, common, and can cause significant economic burden. The impact of skin diseases in the national public healthcare system is complex and poorly studied. This study analyzes the prevalence of skin diseases in a hospital setting within the National Public Health System of Mexico and describes the main associated characteristics.

METHODS

Information was obtained from the 2015 hospital discharge database of the public healthcare system of Mexico. Pathologies that result in a direct dermatological condition were included according to chapter XII of the Tenth Revision of the International Statistical Classification of Diseases and Related Health Problems (ICD - 10) and grouped according to the classification of the report, The burden of skin diseases in the United States.

RESULTS

In 2015, a total of 9,230,968 hospital discharges were registered nationwide, of which 170,917 discharges (1.85%) reported a dermatological disease as the main diagnosis; five states account for 40.79% of the cases reported in Mexico. Half of all the cases corresponded to skin infections (32.08%, n = 54,843) and non-cancerous skin growths (27.80%, n = 47,515), and 59.71% were adult patients between 18 and 65 years of age.

CONCLUSIONS

Understanding of the configuration of skin diseases in a hospital setting and public healthcare system is warranted to develop effective public policies and research for the development of effective, safe, high-quality care processes for the main groups of identified diseases.

Skin and Soft Tissue Infections

The skin is colonized by a diverse collection of microorganisms which, for the most part, peacefully coexist with their hosts. Skin and soft tissue infections (SSTIs) encompass a variety of conditions; in immunocompromised hosts, SSTIs can be caused by diverse microorganisms-most commonly bacteria, but also fungi, viruses, mycobacteria, and protozoa. The diagnosis of SSTIs is difficult because they may commonly masquerade as other clinical syndromes or can be a manifestation of systemic disease. In immunocompromised hosts, SSTI poses a major diagnostic challenge, and clinical dermatological assessment should be initially performed; to better identify the pathogen and to lead to appropriate treatment, etiology should include cultures of lesions and blood, biopsy with histology, specific microbiological analysis with special stains, molecular techniques, and antigen-detection methodologies. Here, we reviewed the epidemiology, pathophysiology, clinical presentation, and diagnostic techniques, including molecular biological techniques, used for SSTIs, with a focus on the immunocompromised host, such as patients with cellular immunodeficiency, HIV, and diabetic foot infection.

Blood cultures in the evaluation of uncomplicated cellulitis

PURPOSE

The frequency of bacteremia and the array of microorganisms involved in cellulitis vary greatly among studies. Although current guidelines do not recommend routine blood culture in uncomplicated cellulitis, their implementation in clinical practice remains challenging. We therefore aimed to assess the frequency, determinants and microbiology of bacteremia in hospitalized patients with uncomplicated cellulitis.

METHODS

We retrospectively reviewed the medical records of all adult patients admitted at a primary-care hospital with a diagnosis of community-acquired uncomplicated cellulitis during a 4-year period. We looked at the factors associated with blood cultures sampling and at the incidence, determinants and microbiology of bacteremia in this population.

RESULTS

Among the 476 patients hospitalized with a diagnosis of cellulitis, 250 (52.5%) had blood cultures. Fever, high C-reactive protein and lymphatic insufficiency were significantly associated with the sampling of blood cultures. Twelve (4.8%) patients had bacteremia. Alcoholism and duration of hospitalization were associated with bacteremia in multivariate analysis. Among the 12 patients with bacteremia, 9 had Streptococcus sp. and 3 had Staphylococcus aureus infection.

CONCLUSION

In our study population with uncomplicated cellulitis, representative of unselected population admitted at primary-care hospitals, bacteremia was uncommon and not associated with discriminant patient characteristics, except for alcohol abuse. Episodes of bacteremia were exclusively due to gram-positive cocci susceptible to co-amoxicilin, a common first-line empirical therapy. In accordance with existing guidelines, we do not recommend to collect blood for cultures in uncomplicated cellulitis. Clinicians' awareness of guidelines and of the poor yield of blood cultures could reduce useless investigation.

The complex relationship between CD4 count, HIV viral load, trimethoprim-sulfamethoxazole prophylaxis, and skin-and-soft-tissue infection risk in patients with HIV: insights from a causal diagram and simulation study

Skin and soft tissue infection (SSTIs) due to Staphylococcus aureus, particularly community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), are common in human immunodeficiency virus (HIV)-infected populations in the United States. Studies have differed as to the importance of epidemiological and immunological factors in this relationship, and have employed conflicting strategies for variable selection in multivariate analyses. Developments in causal inference methods in epidemiology have emerged in the last decade to clarify relationships between variables and identify appropriate variables to include in and exclude from multivariate analysis. In this paper, we develop a causal diagram to clarify the pathways linking CA-MRSA and HIV. We focus on the role played by trimethoprim-sulfamethoxazole (TMP-SMX) prophylaxis, prescribed to many severely immunocompromised HIV patients and potentially protective against SSTIs, which both mediates and moderates the relationship between immunological parameters and SSTI risk. We demonstrate, using simulated data, that statistical models may yield biased results if they do not account for how HIV viral load may also be a marker of adherence to TMP-SMX prophylaxis. We conclude with a proposed causal model that includes both the epidemiological as well as immunological factors that may explain the increased risk of initial and recurrent SSTI risk in HIV-infected populations.

Management of severe non-TB bacterial infection in HIV-infected adults

Despite widespread antiretroviral therapy use, severe bacterial infections (SBI) in HIV-infected adults continue to cause significant morbidity and mortality globally. Four main pathogens account for the majority of documented SBI: Streptococcus pneumoniae, non-typhoidal strains of Salmonella enterica, Escherichia coli and Staphylococcus aureus. The epidemiology of SBI is dynamic, both in developing countries where, despite dramatic successes in antiretroviral therapy, coverage is far from complete, and in settings in both resource-poor and resource-rich countries where antiretroviral therapy failure is becoming increasingly common. Throughout the world, this complexity is further compounded by rapidly emerging antimicrobial resistance, making management of SBI very challenging in these vulnerable patients. We review the causes and treatment of SBI in HIV-infected people and discuss future developments in this field.

Cellulitis-like symptoms manifested by bone metastasis of lung cancer in a patient living with human immunodeficiency virus

Human immunodeficiency virus (HIV)-infected patients are at a high risk of cancer compared with the general population. As the use of antiretroviral therapy (ART) has increased, non-AIDS-defining cancers have also increased in the past decade. A 61-year-old man with HIV infection on ART developed a painful, erythematous and oedematous lower left leg and an associated fever. He was initially treated with antibiotics for cellulitis but there was no improvement, which warranted further investigation. A translucent lesion was found by X-ray imaging and bone scintigraphy showed bone metastasis from a primary adenocarcinoma of the lung, documented by chest computed tomography and an axillary lymph node biopsy. The patient died three months after the diagnosis despite undergoing chemotherapy. This case demonstrates that physicians should consider metastatic malignancies as a differential diagnoses for diverse skin changes in HIV-infected patients.

Risk Factors for Chronic Intertrigo of the Lymphedema Leg in Southern India: A Case-Control Study

Rich clinical experiences indicate that toe web intertrigo is a major predisposing condition for cellulitis/acute dermatolymphango adenitis (ADLA) and the number of lesions is the strongest predictor of frequency of ADLA in lymphedema (LE) patients. However, there is scanty information on the risk factors for the establishment of chronic toe web intertrigo in LE patients. We performed a case-control study recruiting 52 lower limb LE with intertrigo and 52 lower limb LE without intertrigo in community settings and assessed general and local potential risk factors for chronic intertrigo. Analysis of local risk factors revealed that topical application of oil, tingling and numbness of the extremities were associated independently with chronic intertrigo. In multivariate analysis, LE grades III and IV were associated with chronic intertrigo, after adjusting for tingling and numbness, prophylactic antibiotic, age group, and gender. From a public health perspective, LE patients of grades III and IV and patients under antibiotic prophylaxis should be self-motivated to look for the early symptoms of toe web intertrigo to prevent chronic stage and recurrent episodes of cellulitis. Patients with history of tingling and numbness of the periphery need to be monitored for pressure effects leading to poor vascularization and delayed healing of intertrigo.

The Fall of a Dogma? Unexpected High T-Cell Memory Response to Staphylococcus aureus in Humans

INTRODUCTION

Though Staphylococcus aureus is a major pathogen, vaccine trials have failed. In contrast, class-switched antibodies specific to S. aureus are common, implying immune memory formation and suggesting a large pool of S. aureus-reactive helper T-cells.

OBJECTIVE

To elucidate the cellular arm of S. aureus-specific immune memory, the T-cell response in humans was characterized.

METHODS

The proliferative response of human peripheral blood mononuclear cells (PBMCs) to S. aureus antigens and the frequency of S. aureus-specific T-cells were quantified by (3)H-thymidine incorporation; cytokine release was measured by flow cytometry.

RESULTS

Staphylococcus aureus particles and extracellular proteins elicited pronounced proliferation in PBMCs of healthy adults. This reflected a memory response with high frequencies of T-cells being activated by single S. aureus antigens. The whole S. aureus-specific T-cell pool was estimated to comprise 3.6% of T-cells with 35-fold differences between individuals (range, 0.2%-5.7%). When exposed to S. aureus antigens, the T-cells released predominantly but not solely T helper (Th)1/Th17 cytokines.

CONCLUSIONS

The large number of S. aureus antigen-reactive memory T-lymphocytes is likely to influence the course of S. aureus infection. To enable rational vaccine design, the naturally acquired human T-cell memory needs to be explored at high priority.

Predictors of skin and soft tissue infections in HIV-infected outpatients in the community-associated methicillin-resistant Staphylococcus aureus era

Skin and soft tissue infections (SSTIs) are common in the era of community-associated methicillin-resistant Staphylococcus aureus (MRSA) among human immunodeficiency virus (HIV)-infected patients, but the risk factors are not well defined. We sought to elucidate the risk factors for SSTI occurrence in an HIV cohort. This investigation was a retrospective, single-center cohort study, carried out during the period 2005-2009. In this cohort of 511 HIV-infected individuals, 133 SSTIs occurred in 87 individuals over 1,228.6 person-years of follow-up, for an incidence of 108 SSTIs/1,000 person-years [95 % confidence interval (CI) 87-135]. The incidence declined significantly over time (p < 0.01). In a multivariable Cox regression, diabetes [hazard ratio (HR) 2.01; 95 % CI 1.04-3.89], psoriasis (HR 5.77; 95 % CI 1.86-17.9), lymphedema (HR 6.84; 95 % CI 2.59-18.1), intravenous catheter presence (HR 3.38; 95 % CI 1.00-11.5), and HIV viral load greater than 1,000 copies/mL (HR 2.13; 95 % CI 1.33-3.41) were most strongly associated with development of the first SSTI. Trends toward an association between SSTI risk and Medicaid insurance (HR 1.67; 95 % CI 0.98-2.83) and sexually transmitted disease during follow-up (HR 1.66; 0.99-2.78) were present. CD4+ count and trimethoprim-sulfamethoxazole use were not associated with SSTI risk. HIV-infected individuals are at high risk for SSTIs. In a primarily urban, African-American cohort, we found that a number of immunologic and demographic factors were associated with SSTI risk.

The impact of human immunodeficiency virus-related diseases on pigmented skin types

Infection with human immunodeficiency virus (HIV) remains a significant problem globally. Early diagnosis and treatment with antiretroviral drugs has considerably improved health outcomes and decreased disease-related morbidity. HIV infection is associated with a wide range of skin disorders enabling dermatologists to diagnose HIV as well as associated opportunistic infections early in the course of disease. Despite concerted efforts by international health organizations to limit disease incidence, the prevalence of HIV infection remains high and is highest in sub-Saharan Africa. The diagnosis of HIV-related skin diseases is challenging as immunosuppression often results in atypical disease presentation. In addition, the clinical presentation will vary in pigmented skin types. The aim of this article is to describe disease variation in pigmented skin types.

Staphylococcus aureus alpha toxin suppresses effective innate and adaptive immune responses in a murine dermonecrosis model

An optimal host response against Staphylococcus aureus skin and soft tissue infections (SSTI) is dependent on IL-1β and IL-17 mediated abscess formation. Alpha toxin (AT), an essential virulence factor for SSTI, has been reported to damage tissue integrity; however its effect on the immune response has not been investigated. Here, we demonstrate that infection with USA300 AT isogenic mutant (Δhla), or passive immunization with an AT neutralizing mAb, 2A3, 24 h prior to infection with wild type USA300 (WT), resulted in dermonecrotic lesion size reduction, and robust neutrophil infiltration. Infiltration correlates with increase in proinflammatory cytokines and chemokines, as well as enhanced bacterial clearance relative to immunization with a negative control mAb. In addition, infection with Δhla, or with WT +2A3, resulted in an early influx of innate IL-17⁺γδT cells and a more rapid induction of an adaptive immune response as measured by Th1 and Th17 cell recruitment at the site of infection. These results are the first direct evidence of a role for AT in subverting the innate and adaptive immune responses during a S. aureus SSTI. Further, these effects of AT can be overcome with a high affinity anti-AT mAb resulting in a reduction in disease severity.

Fatal Escherichia coli skin and soft tissue infections in liver transplant recipients: report of three cases

Gram-negative bacilli are unusual agents of skin and soft tissue infections. Most previous cases have been reported in cirrhotic or immunocompromised patients, including a single case in a liver transplant recipient. The present report describes 3 cases of fatal skin or soft tissue infections caused by Escherichia coli that occurred in the postoperative course of liver transplantation. The 3 patients were profoundly immunosuppressed as a result of pre-transplant cirrhosis and the postoperative administration of a potent immunosuppressive therapy. Skin and soft tissue infections developed within the first week after liver transplantation, while graft liver function was satisfactory. The 3 patients presented with fever and skin lesions with or without bullae. Despite prompt appropriate antibiotic therapy and surgical debridement, the outcome was rapidly fatal (24 h on average). E. coli was isolated from subcutaneous tissues in 2 cases and from several blood cultures in the third one. The 3 isolates belonged to distinct phylogenetic groups, and did not harbor most of the virulence factors usually reported in extraintestinal pathogenic E. coli isolates. Our report suggests that E. coli can cause severe skin or soft tissue infection in the postoperative course of liver transplantation. The onset of infection is very early and the outcome is extremely poor, despite prompt adapted medical and surgical treatment. Host factors, rather than E. coli bacterial virulence potential, appear to be the major determinants of severity in these patients.

Challenges for a universal Staphylococcus aureus vaccine

This review considers the reasons why the staphylococcal vaccine trials may have failed, based on new information about protective immunity against Staphylococcus aureus. The clinical trials and future vaccine candidate antigens are reviewed. Challenges facing the development of a universal S. aureus vaccine are also considered. The lack of a biomarker that is able to predict protection is a major stumbling block in the development of a staphylococcal vaccine. The major new information involves the role of cell-mediated immunity, specifically T-helper 17 cells and interleukin 17, as well as the lack of protection afforded by specific antibodies. This has major implications for future vaccine development and planning of clinical trials.

Is there a future for a Staphylococcus aureus vaccine?

Multiple attempts to develop a vaccine to prevent Staphylococcus aureus infections have failed. To date, all have been based upon the development of opsonic antibodies. New information suggests that cell mediated immunity may be critical for protection against S. aureus infections. The arm of the immune system that provides the protection contains the Th17/IL-17 axis. Th17 cells release IL-17, which are important for mobilization and activation of neutrophils. Naturally, antibodies aid the neutrophils in the uptake and killing of staphylococci, but immune globulin does not seem to be sufficient to afford protection. New approaches that focus on Th17/IL-17 may allow for the development of a successful S. aureus vaccine.

Innate and adaptive immune responses against Staphylococcus aureus skin infections

Staphylococcus aureus is an important human pathogen that is responsible for the vast majority of bacterial skin and soft tissue infections in humans. S. aureus can also become more invasive and cause life-threatening infections such as bacteremia, pneumonia, abscesses of various organs, meningitis, osteomyelitis, endocarditis, and sepsis. These infections represent a major public health threat due to the enormous numbers of these infections and the widespread emergence of methicillin-resistant S. aureus (MRSA) strains. MSRA is endemic in hospitals worldwide and is rapidly spreading throughout the normal human population in the community. The increasing frequency of MRSA infections has complicated treatment as these strains are more virulent and are increasingly becoming resistant to multiple different classes of antibiotics. The important role of the immune response against S. aureus infections cannot be overemphasized as humans with certain genetic and acquired immunodeficiency disorders are at an increased risk for infection. Understanding the cutaneous immune responses against S. aureus is essential as most of these infections occur or originate from a site of infection or colonization of the skin and mucosa. This review will summarize the innate immune responses against S. aureus skin infections, including antimicrobial peptides that have direct antimicrobial activity against S. aureus as well as pattern recognition receptors and proinflammatory cytokines that promote neutrophil abscess formation in the skin, which is required for bacterial clearance. Finally, we will discuss the recent discoveries involving IL-17-mediated responses, which provide a key link between cutaneous innate and adaptive immune responses against S. aureus skin infections.

Immunity against Staphylococcus aureus cutaneous infections

Complications arising from cutaneous and soft tissue infections with Staphylococcus aureus are a major clinical problem owing to the high incidence of these infections and the widespread emergence of antibiotic-resistant bacterial strains. If prophylactic vaccines or immunotherapy for certain patient populations are to be developed as an alternative to antibiotics, it will be essential to better understand the immune mechanisms that provide protection against S. aureus skin infections. Recent discoveries have identified a key role for interleukin-1 (IL-1)- and IL-17-mediated immune responses in promoting neutrophil recruitment to the site of infection in the skin, a process that is required for host defence and bacterial clearance. This Review describes these new insights and discusses their potential impact on immune-based therapies and vaccination strategies.

IL-17 is essential for host defense against cutaneous Staphylococcus aureus infection in mice

Staphylococcus aureus is the most common cause of skin and soft tissue infections, and rapidly emerging antibiotic-resistant strains are creating a serious public health concern. If immune-based therapies are to be an alternative to antibiotics, greater understanding is needed of the protective immune response against S. aureus infection in the skin. Although neutrophil recruitment is required for immunity against S. aureus, a role for T cells has been suggested. Here, we used a mouse model of S. aureus cutaneous infection to investigate the contribution of T cells to host defense. We found that mice deficient in gammadelta but not alphabeta T cells had substantially larger skin lesions with higher bacterial counts and impaired neutrophil recruitment compared with WT mice. This neutrophil recruitment was dependent upon epidermal Vgamma5+ gammadelta T cell production of IL-17, but not IL-21 and IL-22. Furthermore, IL-17 induction required IL-1, TLR2, and IL-23 and was critical for host defense, since IL-17R-deficient mice had a phenotype similar to that of gammadelta T cell-deficient mice. Importantly, gammadelta T cell-deficient mice inoculated with S. aureus and treated with a single dose of recombinant IL-17 had lesion sizes and bacterial counts resembling those of WT mice, demonstrating that IL-17 could restore the impaired immunity in these mice. Our study defines what we believe to be a novel role for IL-17-producing epidermal gammadelta T cells in innate immunity against S. aureus cutaneous infection.

Focal Salmonella enteritidis infection in a patient with HIV infection and other multiple causes of immunodeficiency

An HIV-infected man receiving antiretroviral therapy-who also had lupus-like vasculitis and membranous glomerulonephritis (treated with prednisolone and azathioprine), beta-thalassaemia minor trait and post-radiotherapy functional asplenia (mimicking sickle cell disease-induced hyposplenism)-developed focal soft issue and bone infection caused by Salmonella enteritidis at the site of previous mycobacterial infection.

The immunomodulatory Pseudomonas aeruginosa signalling molecule N ‐(3‐oxododecanoyl)‐ l ‐homoserine lactone enters mammalian cells in an unregulated fashion

The Pseudomonas aeruginosa quorum-sensing signal molecule N-3-oxododecanoyl)-L-homoserine lactone (OdDHL) has been reported to affect the function of a wide range of mammalian cell types, including cells of the immune system. In T cells, it has been reported to inhibit the production of most cytokines, and it has been reported to inhibit the function of antigen-presenting cells. The intracellular target of OdDHL in these cells remains to be identified, although the lipophilic nature of the molecule suggested that the target could be membrane associated. We explored the association of radiolabelled OdDHL with the membrane and cytoplasm of Jurkat T-cell lines and of primary murine T cells and dendritic cells. We found that not only did 3H-OdDHL enter the cytoplasm of Jurkat cells without disproportionate association with the cell membrane, it also reached maximum levels in the cytoplasm very quickly, and that the intracellular concentration was proportional to the extracellular concentration. Similar results were obtained when 3H-OdDHL was incubated with primary murine T cells or cultured dendritic cells. In addition, we show that the cellular distribution of OdDHL does not significantly alter after stimulation of Jurkat cells or primary murine CD4 T cells with immobilized anti-CD3, with little activity being associated with nuclear fractions. Together, these data strongly suggest that OdDHL enters mammalian cells by passive mechanisms, and that it does not preferentially associate with the membrane or nucleus upon T-cell receptor ligation.

Children hospitalized with skin and soft tissue infections: a guide to antibacterial selection and treatment

Skin and soft tissue infections in children are an important cause for hospitalization. A thorough history and physical examination can provide clues to the pathogens involved. Collection of purulent discharge from lesions should be completed prior to initiating antimicrobial therapy, and results of bacteriologic studies (Gram stain and culture) should guide therapeutic decisions. The main pathogens involved in these infections are Staphylococcus aureus and group A beta-hemolytic streptococci, but enteric organisms also play a role especially in nosocomial infections. Increasing antibacterial resistance is becoming a major problem in the treatment of these infections worldwide. Specifically, the rise of methicillin-resistant S. aureus and glycopeptide-resistant S. aureus pose challenges for the future. Infections of the skin and soft tissues can be broadly classified based on the extent of tissue involvement. Superficial infections such as erysipelas, cellulitis, bullous impetigo, bite infections, and periorbital cellulitis may require hospitalization and parenteral antibacterials. Deeper infections such as orbital cellulitis, necrotizing fasciitis, and pyomyositis require surgical intervention as well as parenteral antibacterial therapy. Surgery plays a key role in the treatment of abscesses and for the debridement of necrotic tissue in deep infections. Intravenous immunoglobulin, as an adjunctive therapy, can be helpful in treating necrotizing fasciitis. For most infections an antistaphylococcal beta-lactam antibacterial is first-line therapy. Third-generation cephalosporins and beta-lactam/beta-lactamase inhibitor antibacterials as well as clindamycin or metronidazole are often required to provide broad-spectrum coverage for polymicrobial infections.Special populations, such as immunocompromised children, those with an allergy to penicillins, and those that acquire infections in hospitals, require specific antibacterial strategies. These usually involve broader antimicrobial coverage with increased Gram-negative (including antipseudomonal) and anerobic coverage. In patients with a true allergy to penicillins, clindamycin and vancomycin play an important role in treating Gram-positive infections. Newer antibacterial agents, such as linezolid and quinupristin/dalfopristin, are increasingly being studied in children for the treatment of skin and soft tissue infections. These agents hold promise for the future especially in the treatment of highly resistant, Gram-positive organisms such as methicillin-resistant S. aureus, vancomycin-resistant S. aureus, and vancomycin-resistant enterococci.

Risk factors for bacteremia in patients with limb cellulitis

The aim of this study was to identify the risk factors for bacteremia in patients with limb cellulitis. Using the administrative and microbiology laboratory databases of a community teaching hospital, a review was conducted of all cases of community-acquired limb cellulitis that occurred during the period 1997-2004 and in which blood cultures had been performed. A comparison of demographical, clinical, and analytical data of patients with bacteremia versus patients without bacteremia was performed by univariate and multivariate analyses. Of 2,678 patients with cellulitis who presented to the hospital's emergency department, 308 were diagnosed with limb cellulitis and had blood cultures. Of these, 57 (18.5%) had bacteremia. In 24 of the 57 (42.1%) patients with bacteremia, the microorganism isolated in blood cultures was non-group-A beta-hemolytic Streptococcus, and in another 14 (24.6%), the microorganism identified was a gram-negative bacterium. Staphylococcus aureus was determined as the cause of bacteremia in just 6 (10.5%) patients and group A Streptococcus in 2 (3.5%). By logistic regression analysis, the following factors were associated with bacteremia: absence of previous antibiotic treatment (OR 5.3, 95% CI 1.4-20.3), presence of two or more comorbid factors simultaneously (OR 4.3, 95% CI 1.6-11.7), length of illness<2 days OR 2.44, 95% CI 1.07-5.56), and proximal limb involvement (OR 6, 95% CI 3.03-12.04). Patients with limb cellulitis who exhibit any of these characteristics are at increased risk of bacteremia. In such patients, it is imperative that blood cultures be performed.

Staphylococcal skin infections in children: rational drug therapy recommendations

Staphylococcus aureus remains one of the most common and troublesome of bacteria causing disease in humans, despite the development of effective antibacterials and improvement in hygiene. The organism is responsible for over 70% of all skin and soft tissue infections in children and accounts for up to one-fifth of all visits to pediatric clinics. Skin and soft tissue infections that are predominantly caused by S. aureus include bullous and non-bullous impetigo, folliculitis, furunculosis, carbunculosis, cellulitis, surgical and traumatic wound infections, mastitis, and neonatal omphalitis. Other skin and soft tissue infections may also be caused by S. aureus but are often polymicrobial in origin and require special consideration. These include burns, decubitus ulcers (particularly in the perianal region), puncture wounds of the foot, as well as human and mammalian bites. Treatment of staphylococcal skin infections varies from topical antiseptics to prolonged intravenous antibacterials, depending on severity of the lesions and the health of the child. The treatment of choice for oral antibacterials remains the penicillinase-resistant penicillins such as flucloxacillin. Cefalexin and erythromycin are suitable cost-effective alternatives with broader cover, although care must be taken with the use of macrolides because of development of resistance to multiple families of antibacterials, particularly the lincosamides. Other cephalosporins such as cefadroxil and cefprozil are also effective, can be given once daily and have a better tolerability profile -- while azithromycin has a further advantage of a 3-day course. However, all of these agents are more expensive. Although the antibacterials have been given for 10 days in most clinical trials, there is no evidence that this duration is more effective than a 7-day course. In children requiring intravenous therapy, ceftriaxone has a major advantage over other antibacterials such as sulbactam/ampicillin and cefuroxime in that it can be given once daily and may, therefore, be suitable for outpatient treatment of moderate-to-severe skin infections. Newer-generation cephalosporins and loracarbef are also effective and have a broader spectrum of activity, but do not offer any added benefit and are significantly more expensive. Skin and soft tissue infections due to methicillin-resistant S. aureus (MRSA) are still relatively uncommon in children. Well children with community-acquired MRSA infections can be treated with clindamycin or trimethoprim-sulfamethoxazole (cotrimoxazole), but must be observed closely for potentially severe adverse effects. In severe infections, vancomycin remains the treatment of choice, while intravenous teicoplanin and clindamycin are suitable alternatives. Linezolid and quinupristin/dalfopristin are currently showing great promise for the treatment of multi-resistant Gram-positive infections. While the choice of antibacterial is important, supportive management, including removal of any infected foreign bodies, surgical drainage of walled-off lesions, and regular wound cleaning, play a vital role in ensuring cure.

Cellulitis incidence in a defined population

A population-based insurance claims database was used to examine cellulitis incidence, anatomical sites of infection, complicating diagnoses, source of health service, and recurrence rates. Insurance claim files were searched for cellulitis ICD-9-CM codes 681.0-682.9. Complications of cellulitis including erysipelas, lymphadenitis, lymphangitis, and necrotizing fasciitis were also identified by ICD-9-CM codes. We found a cellulitis incidence rate of 24.6/1000 person-years, with a higher incidence among males and individuals aged 45-64 years. The most common site of infection was the lower extremity (39.9%). The majority of patients were seen in an outpatient setting (73.8%), and most (82.0%) had only one episode of cellulitis during the 5-year period studied. There was a very low incidence of cellulitis complications, including necrotizing fasciitis. Cellulitis is fairly common, usually treated in outpatient settings, and is infrequently complicated by erysipelas, lymphadenitis, lymphangitis, or necrotizing fasciitis.

Seasonal variation in undiagnosed HIV infection on the general medicine and trauma services of two urban hospitals

OBJECTIVE

To examine the seroprevalence of undiagnosed HIV and variation by season among patients admitted to the general internal medicine (GIM) and trauma services of two urban hospitals.

DESIGN

A cross-sectional blinded HIV-1 seroprevalence survey.

SETTING

A 725-bed academic medical center's hospital and an affiliated 324-bed tertiary care hospital.

PARTICIPANTS

Residual serological specimens were obtained for unique patients aged 17 to 65 to study services in summer (June 16 to September 4, 2001) and fall to winter (November 1, 2001 to January 8, 2002).

METHODS

Hospital files provided data on demographics, service type, and discharge clinical categories (fall-winter group only). HIV ELISA (enzyme-linked immunosorbent assay) tests with confirmatory Western blot were linked to subjects' de-identified files. We excluded 34 subjects with known HIV. Of the remaining unique admissions in summer (n=604) and fall-winter (n=978), 60% and 55% were tested, respectively. Predictors of undiagnosed HIV infection were examined using multivariate analysis.

RESULTS

The summer cohort (n=362) had significantly lower unadjusted seroprevalence of undiagnosed HIV infection (1.4%; 95% confidence interval [CI], 0.4% to 3.2%) than the fall-winter cohort (n=539; 3.7%; 95% CI, 2.3% to 5.7%; P=.04). Overall, undiagnosed HIV was somewhat less likely in women (adjusted odds ratio [AOR], 0.45; 95% CI, 0.19 to 1.07) but more likely in black patients (AOR, 3.46; 95% CI, 0.70 to 17.06). In the fall-winter cohort, undiagnosed HIV was more likely for discharges with the following clinical categories versus those with a cardiac condition: dermatologic/breast (AOR, 14.90; 95% CI, 1.20 to 184.77), renal/urological (AOR, 22.43; 95% CI, 2.12 to 236.75), or infectious (AOR, 31.08; 95% CI, 2.40 to 402.98).

CONCLUSIONS

The higher seroprevalence of undiagnosed HIV in the fall-winter admissions to GIM and trauma services supports especially targeting HIV testing in these months.

A practical guide to the treatment of complicated skin and soft tissue infections

Complicated skin and soft tissue infections (SSTIs) remain a common reason for hospitalisation. Optimal management of complicated SSTIs begins with a physical examination, and obtaining the complete social and medical history of the patient. Empirical intravenous antibacterial therapy is guided by expected pathogens, patient factors and diagnostic procedure reports, such as the Gram-stained smear of discharge or exudates. The majority of community-acquired SSTIs are caused by Staphylococcus aureus and beta-haemolytic streptococci. On the basis of recent surveillance data, 80-90% of these pathogens remain susceptible to cefazolin or oxacillin. Consequently, a first generation cephalosporin or an antistaphylococcal penicillin remains the first line empirical therapy for community-acquired skin and soft tissue infections. Vancomycin may be an appropriate alternative when vancomycin-resistant S. aureus is highly suspected on the basis of patient history and co-morbid conditions. With the global emergence and spread of macrolide-resistant S. aureus and beta-haemolytic streptococci, clindamycin rather than a macrolide is the recommended agent for empirical antibacterial therapy of community-acquired SSTIs in penicillin-allergic patients. Nosocomial complicated SSTIs are predominantly caused by S. aureus, Pseudomonas aeruginosa, Enterococcus spp., Escherichia coli and other Enterobacteriaceae. Piperacillin/tazobactam with or without vancomycin is the preferred agent for empirical treatment depending on local resistance statistics. The newer fluoroquinolones may have a role in the treatment of complicated SSTIs, especially in penicillin-allergic patients. More clinical studies are needed before a formal recommendation can be made. Many of the newer antimicrobial agents such as the carbapenems, oxazolidinones and streptogramins have been shown to be effective for the treatment of complicated SSTIs. However, because of their proven activity against highly resistant organisms including methicillin-resistant S. aureus and vancomycin-resistant enterococci (oxazolidinones and streptogramins), and Gram-negative bacilli producing extended spectrum beta-lactamases (carbapenems), these antibacterials should be reserved for life-threatening situations and/or when resistant pathogens are suspected. Complicated skin and soft tissue infections are often associated with exudates, ulcerations, fluid collections or abscesses. Adequate debridement of devitalized tissues and drainage of abscesses and fluid collections in addition to systemic antibacterial therapy is an integral part of appropriate management.

In vitro metabolism of clindamycin in human liver and intestinal microsomes

Incubations with human liver and gut microsomes revealed that the antibiotic, clindamycin, is primarily oxidized to form clindamycin sulfoxide. In this report, evidence is presented that the S-oxidation of clindamycin is primarily mediated by CYP3A. This conclusion is based upon several lines of in vitro evidence, including the following. 1) Incubations with clindamycin in hepatic microsomes from a panel of human donors showed that clindamycin sulfoxide formation correlated with CYP3A-catalyzed testosterone 6beta-hydroxylase activity; 2) coincubation with ketaconazole, a CYP3A4-specific inhibitor, markedly inhibited clindamycin S-oxidase activity; and 3) when clindamycin was incubated across a battery of recombinant heterologously expressed human cytochrome P450 (P450) enzymes, CYP3A4 possessed the highest clindamycin S-oxidase activity. A potential role for flavin-containing monooxygenases (FMOs) in clindamycin S-oxidation in human liver was also evaluated. Formation of clindamycin sulfoxide in human liver microsomes was unaffected either by heat pretreatment or by chemical inhibition (e.g., methimazole). Furthermore, incubations with recombinant FMO isoforms revealed no detectable activity toward the formation of clindamycin sulfoxide. Beyond identifying the drug-metabolizing enzyme responsible for clindamycin S-oxidation, the ability of clindamycin to inhibit six human P450 enzymes was also evaluated. Of the P450 enzymes examined, only the activity of CYP3A4 was inhibited (approximately 26%) by coincubation with clindamycin (100 microM). Thus, it is concluded that CYP3A4 appears to account for the largest proportion of the observed P450 catalytic clindamycin S-oxidase activity in vitro, and this activity may be extrapolated to the in vivo condition.