Burn Injury Leads to Increased Long-Term Susceptibility to Respiratory Infection in both Mouse Models and Population Studies

Long term mortality in burn injury survivors: A matched cohort study

BACKGROUND

Survivors of burn injuries may be at risk of early death. This study describes the mortality of burn survivors in comparison with two matched cohorts.

METHODS

This retrospective cohort study compared adults admitted with a burn injury from 2009 to 2019 with two matched cohorts; one from the general population and one with a diagnosis of acute pancreatitis. Patients were excluded from analysis if they died during hospital admission or within 90 days of hospital discharge. Cox proportional hazards models were used to explore differences between cohorts and variables associated with mortality.

RESULTS

7,147 burns patients were matched with 6,810 pancreatitis patients and 28,184 individuals from the general population. Patients with a burn injury had an increased risk of death when compared to the general population (HR 2.46, 95 % CI 2.28,2.66, p < 0.001) and those with acute pancreatitis (HR 1.28, 95 % CI 1.17,1.40, p < 0.001). Socioeconomic deprivation, increasing comorbidity and specific comorbidities such as alcohol, drug abuse and depression were also associated with increased mortality.

CONCLUSION

Survivors of burn injury are at increased risk of mortality compared to individuals matched on sex, age and socioeconomic deprivation in both the general population and with a hospital admission due to acute pancreatitis.

Non-severe thermal burn injuries induce long-lasting downregulation of gene expression in cortical excitatory neurons and microglia

Burn injuries are devastating traumas, often leading to life-long consequences that extend beyond the observable burn scar. In the context of the nervous system, burn injury patients commonly develop chronic neurological disorders and have been suggested to have impaired motor cortex function, but the long-lasting impact on neurons and glia in the brain is unknown. Using a mouse model of non-severe burn injury, excitatory and inhibitory neurons in the primary motor cortex were labelled with fluorescent proteins using adeno-associated viruses (AAVs). A total of 5 weeks following the burn injury, virus labelled excitatory and inhibitory neurons were isolated using fluorescence-activated cell sorting (FACS). In addition, microglia and astrocytes from the remaining cortical tissue caudal to the motor cortex were immunolabelled and isolated with FACS. Whole transcriptome RNA-sequencing was used to identify any long-lasting changes to gene expression in the different cell types. RNA-seq analysis showed changes to the expression of a small number of genes with known functions in excitatory neurons and microglia, but not in inhibitory neurons or astrocytes. Specifically, genes related to GABA-A receptors in excitatory neurons and several cellular functions in microglia were found to be downregulated in burn injured mice. These findings suggest that non-severe burn injuries lead to long lasting transcriptomic changes in the brain, but only in specific cell types. Our findings provide a broad overview of the long-lasting impact of burn injuries on the central nervous system which may help identify potential therapeutic targets to prevent neurological dysfunction in burn patients.

Infections in Burn Patients

Infections are the leading cause of mortality in burn patients who survive their initial resuscitation. Burn injury leads to immunosuppression and a dysregulated inflammatory response which can have a prolonged impact. Early surgical excision along with support of the multidisciplinary burn team has improved mortality in burn patients. The authors review diagnostic and therapeutic challenges as well as strategies for management of burn related infections.

Pseudomonas aeruginosa: Infections, Animal Modeling, and Therapeutics

Pseudomonas aeruginosa is an important Gram-negative opportunistic pathogen which causes many severe acute and chronic infections with high morbidity, and mortality rates as high as 40%. What makes P. aeruginosa a particularly challenging pathogen is its high intrinsic and acquired resistance to many of the available antibiotics. In this review, we review the important acute and chronic infections caused by this pathogen. We next discuss various animal models which have been developed to evaluate P. aeruginosa pathogenesis and assess therapeutics against this pathogen. Next, we review current treatments (antibiotics and vaccines) and provide an overview of their efficacies and their limitations. Finally, we highlight exciting literature on novel antibiotic-free strategies to control P. aeruginosa infections.

Characteristics and prognosis of Herpesviridae-related pneumonia in critically ill burn patients

BACKGROUND

The aim of this study was to describe the prevalence, characteristics and outcome of critically burn patients with pulmonary HSV reactivation.

METHODS

Retrospective, single-center cohort study in a burn critical care unit in a tertiary center, including all consecutive severely burn patients with bronchoalveolar lavage performed for pneumoniae suspicion and screened for HSV from January 2013 and April 2017. We used logistic regression to identify factors associated with HSV reactivation and outcomes.

RESULTS

94 patients were included, mean age was 51 (39-64) years; median total body surface area burned was 36 (25-54)% and ICU mortality 38%. Fifty-five patients (59%) had pulmonary HSV reactivation and 30 (55%) were treated with acyclovir. Patients with HSV reactivation were more severely ill with higher SOFA score at admission compared to patient without HSV reactivation (6 [3-8] vs. 2 [1-4], p < 0.0001 respectively). In multivariate analysis, sex, SOFA score at admission and smoke inhalation were significantly associated with HSV reactivation. Only septic shock was associated with 90-day mortality when HSV reactivation was not.

CONCLUSIONS

Pulmonary HSV reactivation is frequent among severely ill burn patients. Initial severity and smoke inhalation are risk factors. Antiviral treatment was not associated with outcome.

A case of Flavonifractor plautii blood stream infection in a severe burn patient and a review of the literature

BACKGROUND

Flavonifractor plautii is a strictly anaerobic rod shaped bacterium belonging to the family of Clostridiales. It is a commensal of the human intestinal microbiota which was seldom isolated from clinical samples, therefore clinical data are scarce. To date, only four cases of F. plautii infections were described, all occurring in immunosuppressed patients.

CASE PRESENTATION

We report a case where F. plautii was isolated from the blood culture of a severe burn victim and identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry.

DISCUSSION

To the best of our knowledge, this is the first case of F. plautii blood stream infection described in a burn patient.

Climate Change and Infections on the Move in North America

Climate change is increasingly recognized for its impacts on human health, including how biotic and abiotic factors are driving shifts in infectious disease. Changes in ecological conditions and processes due to temperature and precipitation fluctuations and intensified disturbance regimes are affecting infectious pathogen transmission, habitat, hosts, and the characteristics of pathogens themselves. Understanding the relationships between climate change and infectious diseases can help clinicians broaden the scope of differential diagnoses when interviewing, diagnosing, and treating patients presenting with infections lacking obvious agents or transmission pathways. Here, we highlight key examples of how the mechanisms of climate change affect infectious diseases associated with water, fire, land, insects, and human transmission pathways in the hope of expanding the analytical framework for infectious disease diagnoses. Increased awareness of these relationships can help prepare both clinical physicians and epidemiologists for continued impacts of climate change on infectious disease in the future.

Non-severe burn injury increases cancer incidence in mice and has long-term impacts on the activation and function of T cells

Background

Recent evidence suggests that burn patients are at increased risk of hospital admission for infection, mental health conditions, cardiovascular disease and cancer for many years after discharge for the burn injury itself. Burn injury has also been shown to induce sustained immune system dysfunction. This change to immune function may contribute to the increased risk of chronic disease observed. However, the mechanisms that disrupt long-term immune function in response to burn trauma, and their link to long-term morbidity, remain unknown. In this study we investigated changes to immune function after burn injury using a murine model of non-severe injury.

Methods

An established mouse model of non-severe burn injury (full thickness burn equivalent to 8% total body surface area) was used in combination with an orthotopic model of B16 melanoma to investigate the link between burns and cancer. Considering that CD8⁺ T cells are important drivers of effective tumour suppression in this model, we also investigated potential dysregulation of this immune population using mouse models of burn injury in combination with herpes simplex virus infection. Flow cytometry was used to detect and quantify cell populations of interest and changes in immune function.

Results

We demonstrate that 4 weeks after a non-severe burn injury, mice were significantly more susceptible to tumour development than controls using an orthotopic model of B16 melanoma. In addition, our results reveal that CD8⁺ T cell expansion, differentiation and memory potential is significantly impaired at 1 month post-burn.

Conclusions

Our data suggests that CD8⁺ T cell-mediated immunity may be dysfunctional for a sustained period after even non-severe burn injury. Further studies in patients to validate these findings may support clinical intervention to restore or protect immunity in patients after burn injury and reduce the increased risk of secondary morbidities observed.

Large animal models of thermal injury

Burn injury results in a triad of inter-related adaptive responses: a systemic inflammatory response, a stress response, and a consequent hypermetabolic state which supports the former two. These pathological responses extend beyond the site of injury to affect distant organs and influence long-term outcomes in the patient. Animal models have proven valuable in advancing our understanding of mechanisms underlying the multifactorial manifestations of burn injury. While rodent models have been unprecedented in providing insights into signaling pathways, metabolic responses, protein turnover, cellular and molecular changes; small animal models do not replicate hypermetabolism, hyperinflammation, and wound healing after a burn injury as seen in humans. Herein, we provide a concise review of preferred large animal models utilized to understand burn pathophysiology based on organ systems and associated dysfunction. Additionally, we present a detailed protocol of contact burn injury in the Yorkshire pig model with a focus on preoperative care, anesthesia, analgesia, wound excision and grafting, dressing application, and frequency of dressing changes.

Multicentre, longitudinal, observational cohort study to examine the relationship between neutrophil function and sepsis in adults and children with severe thermal injuries: a protocol for the Scientific Investigation of the Biological Pathways Following Thermal Injury-2 (SIFTI-2) study

INTRODUCTION

Burn-induced changes in the phenotype and function of neutrophils, cells which provide front-line protection against rapidly dividing bacterial infections, are emerging as potential biomarkers for the early prediction of sepsis. In a longitudinal study of adult burns patients, we recently demonstrated that a combined measurement of neutrophil phagocytic capacity, immature granulocyte (IG) count and plasma cell-free DNA (cfDNA) levels on the day of injury gave good discriminatory power for the prediction of later sepsis development. However, limited by a small sample size, single-centre design and focus on adult burns patients, these biomarkers require prospective validation in a larger patient cohort. The Scientific Investigation of the Biological Pathways Following Thermal Injury-2 study aims to prospectively validate neutrophil phagocytic activity, IG count and plasma cfDNA levels as early prognostic biomarkers of sepsis in thermally injured adult and paediatric patients.

METHODS AND ANALYSIS

This multicentre, longitudinal, observational cohort study will enrol 245 paediatric and adult patients with moderate to severe burns within 24 hours of injury. Blood samples will be obtained at 19 postinjury time points (days 1-14, day 28, months 3, 6, 12 and 24) and analysed for neutrophil phagocytic activity, IG count and cfDNA levels. Patients will be screened daily for sepsis using the 2007 American Burn Association diagnostic criteria for sepsis. In addition, daily multiple organ dysfunction syndrome and Sequential Organ Failure Assessment Scores will be recorded relationships between neutrophil phagocytic activity, IG count and plasma cfDNA levels on day 1 of injury and the development of sepsis will be examined using logistic regression models.

ETHICS AND DISSEMINATION

This study received ethics approval from the West Midlands, Coventry and Warwickshire Research Ethics Committee (REC reference:16/WM/0217). Findings will be presented at national and international conferences, and submitted for publication in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT04693442.

Recommendations for influenza vaccination in burns patients based on a systematic review of the evidence

Severe burn injury is a serious systemic insult that can lead to life threatening secondary infections. Immunosuppression, inhalation injury and prolonged length of hospital stay are factors which predispose patients to severe respiratory tract infections. Furthermore, evidence shows that burns can put one at risk of infection long after the original injury. Currently in the United Kingdom, the annual National Flu Immunisation programme outlines guidance for groups who are deemed high risk and therefore eligible for the influenza vaccine. At present, no guidance exists for administration of the influenza vaccine in burn injured patients, despite knowledge of immunosuppression. The aim of this literature review is to examine the evidence for associations between burn injury and influenza and where available, evaluate efficacy of influenza vaccines in this cohort. In addition, literature was searched for the effectiveness of the influenza vaccine in patients 65 years and above, and in patients admitted to the intensive care unit (ICU); two domains common to patients with severe burns. Three papers were found to suggest increased susceptibility to influenza following burn injury, however no papers studying the effectiveness of the influenza vaccine in this group were found. Several studies demonstrated improved outcomes in patients over 65 years and patients admitted to ICU. Following evaluation of the evidence, this review advocates for the consideration of hospitalized burn patients for the influenza vaccine. We suggest avoidance of vaccine administration in the acute burn phase. Further prospective clinical trials would be required to validate these findings.

Protective Effects of Melatonin against Severe Burn-Induced Distant Organ Injury: A Systematic Review and Meta-Analysis of Experimental Studies

Extensive burns result in a local wound response and distant-organ injury (DOI) caused by oxidative-stress and inflammation. Melatonin (MT) shows promise in alleviating oxidative-stress and inflammation, but its role in thermal injury is largely unexplored. The present systematic review and meta-analysis were designed to assess the effects of MT on oxidative-stress and inflammatory markers against severe burn-induced DOI. Mean difference (MD)/standard mean difference (SMD) with 95% confidence interval (CI) were estimated using fixed-effect/random-effects models. Eighteen experimental studies met the inclusion criteria. Compared with the control group, MT significantly decreased the levels of malondialdehyde (SMD, −1.03; 95% CI, −1.30, −0.76, p < 0.00001) and 4-hydroxynonenal (MD, −1.06; 95% CI, −1.57, −0.56, p < 0.0001). Additionally, MT increased the levels of glutathione (SMD, 1.94; 95% CI, 1.27, 2.61, p < 0.00001) and superoxide-dismutase (SMD, 0.76; 95% CI, 0.08, 1.45, p = 0.03). Finally, MT significantly decreased the levels of tumor necrosis factor-α (SMD, −1.34; 95% CI, −1.92 to −0.77; p < 0.00001) and C-reactive protein (MD, −12.67; 95% CI, −16.72 to −8.62; p < 0.00001). Meta-analysis indicates that severe burn followed by immediate MT (10 mg/kg) intervention shows significant beneficial effects after 24-h against DOI by regulating oxidative-stress and the inflammatory response.

Viral Infections in Burn Patients: A State-Of-The-Art Review

Infections that are triggered by the accompanying immunosuppression in patients with burn wounds are very common regardless of age. Among burn patients, the most frequently diagnosed infections include the bacterial ones primarily caused by Pseudomonas aeruginosa or Klebsiella pneumonia, as well as fungal infections with the etiology of Candida spp. or Aspergillus spp. Besides, burn wounds are highly susceptible to viral infections mainly due to the impaired immune responses and defective functions of the immune cells within the wound microenvironment. The most prevalent viruses that invade burn wounds include herpes simplex virus (HSV), cytomegalovirus (CMV), human papilloma virus (HPV), and varicella zoster virus (VZV). Likewise, less prevalent infections such as those caused by the orf virus or Epstein-Barr Virus (EBV) might also occur in immunosuppressed burn patients. Viral infections result in increased morbidity and mortality rates in severely burned patients. Additionally, a positive correlation between the hospitalization duration and the severity of the viral infection has been demonstrated. Viral infections trigger the occurrence of various complications, ranging from mild symptoms to even fatal incidents. Accurate detection of viral infection is of great clinical importance because of the possibility for a quicker introduction of proper treatment therapy and shortening of hospitalization time. The aim of this paper is to provide a comprehensive review of the literature and summarize the findings regarding the most common viral infections in immunosuppressed burn patients.

Pediatric Burn Survivors Have Long-Term Immune Dysfunction With Diminished Vaccine Response

Epidemiological studies have demonstrated that survivors of acute burn trauma are at long-term increased risk of developing a range of morbidities. The mechanisms underlying this increased risk remain unknown. This study aimed to determine whether burn injury leads to sustained immune dysfunction that may underpin long-term morbidity. Plasma and peripheral blood mononuclear cells were collected from 36 pediatric burn survivors >3 years after a non-severe burn injury (<10% total body surface area) and from age/sex-matched non-injured controls. Circulating cytokine and vaccine antibody levels were assessed using multiplex immunoassays and cell profiles compared using a panel of 40 metal-conjugated antibodies and mass cytometry. TNF-α (1.31-fold change from controls), IL-2 (1.18-fold), IL-7 (1.63-fold), and IFN-γ (1.18-fold) were all significantly elevated in the burn cohort. Additionally, burn survivors demonstrated diminished antibody responses to the diphtheria, tetanus, and pertussis vaccine antigens. Comparisons between groups using unsupervised clustering identified differences in proportions of clusters within T-cells, B-cells and myeloid cells. Manual gating confirmed increased memory T-regulatory and central memory CD4+ T-cells, with altered expression of T-cell, B-cell, and dendritic cell markers. Conclusions: This study demonstrates a lasting change to the immune profile of pediatric burn survivors, and highlights the need for further research into post-burn immune suppression and regulation.

Scald Injury-Induced T Cell Dysfunction Can Be Mitigated by Gr1+ Cell Depletion and Blockage of CD47/CD172a Signaling

Infection is a common and severe complication of burn injury: Sepsis accounts for 47% of postburn mortality. Burn-induced T cell suppression likely contributes to the increased infection susceptibility in burn patients. However, little is known about the kinetics of T cell dysfunction after burn and its underlying mechanisms. In this study, we show in a murine scald injury model that T cell activation of both CD4⁺ and CD8⁺ T cells as well as T cell cytokine production is suppressed acutely and persistently for at least 11 days after burn injury. Purified T cells from scald-injured mice exhibit normal T cell functions, indicating an extrinsically mediated defect. We further show that T cell dysfunction after burn appears to be cell-to-cell contact dependent and can be ameliorated by depletion of myeloid-derived suppressor cells. These cells expand after burn injury, particularly a subset expressing the checkpoint inhibitor CD172a, and infiltrate germinal centers. Expression of CD172a appears to be driven by ingestion of immature reticulocytes. Immature reticulocytes are drastically increased in the spleen of scald mice and may contribute to immunosuppression through more direct mechanisms as well. Overall, our study newly identifies two cell populations, myeloid-derived suppressor cells and immature reticulocytes, as well as the CD47/CD172a-signaling pathways as mediators of T cell suppressors after burn and thus opens up new research opportunities in the search for new therapies to combat increased infection susceptibility and the associated morbidity and mortality in burn victims.

Seasonal flu-vaccination in the immunocompromised burns patient

BACKGROUND AND AIMS

Influenza is a serious disease which can be life threatening. Patients with significant burns have reduced physiological reserve and are at risk both of incurring dangerous respiratory complications. In other susceptible patient groups the flu vaccine is used to reduce the risk of flu and lessen its effects. We aim to investigate whether there were any existing local and national trends in the use of flu vaccination in burns patients. Our second objective was to review any current evidence in the literature.

METHODS

A questionnaire was carried out of consultants in our own health board and of 5 of the major burns units in the UK to assess current practice.

RESULTS

None of the local respondent were aware of any existing guidelines. None of the external units contacted reported the use of a guideline for flu vaccination in burns patients. On searching the literature there were no existing studies investigating the use of flu vaccination in burns patients.

CONCLUSIONS

Through review of the literature on flu vaccination in immunocompromised patients we show how this could be extrapolated to patients with significant burns. We propose a guideline to aid in the decision to prescribe flu vaccine to patients with significant burns taking into account age, % TBSA burn and comorbidity. The decision to recommend the flu vaccine in this group should be considered on an individual basis. However, flu vaccination represents a simple, low-risk measure which could prevent the dangerous complications of influenza in an at risk group.

Understanding acute burn injury as a chronic disease

While treatment for burn injury has improved significantly over the past few decades, reducing mortality and improving patient outcomes, recent evidence has revealed that burn injury is associated with a number of secondary pathologies, many of which arise long after the initial injury has healed. Population studies have linked burn injury with increased risk of cancer, cardiovascular disease, nervous system disorders, diabetes, musculoskeletal disorders, gastrointestinal disease, infections, anxiety and depression. The wide range of secondary pathologies indicates that burn can cause sustained disruption of homeostasis, presenting new challenges for post-burn care. Understanding burn injury as a chronic disease will improve patient care, providing evidence for better long-term support and monitoring of patients. Through focused research into the mechanisms underpinning long-term dysfunction, a better understanding of burn injury pathology may help with the development of preventative treatments to improve long-term health outcomes. The review will outline evidence of long-term health effects, possible mechanisms linking burn injury to long-term health and current research into burns as a chronic disease.

Long-term mental health outcomes after unintentional burns sustained during childhood: a retrospective cohort study

Background

Burns are a devastating injury that can cause physical and psychological issues. Limited data exist on long-term mental health (MH) after unintentional burns sustained during childhood. This study assessed long-term MH admissions after paediatric burns.

Methods

This retrospective cohort study included all children (< 18 years) hospitalised for a first burn (n = 11,967) in Western Australia, 1980-2012, and a frequency matched uninjured comparison cohort (n = 46,548). Linked hospital, MH and death data were examined. Multivariable negative binomial regression modelling was used to generate incidence rate ratios (IRR) and 95% confidence intervals (CI).

Results

The burn cohort had a significantly higher adjusted rate of post-burn MH admissions compared to the uninjured cohort (IRR, 95% CI: 2.55, 2.07-3.15). Post-burn MH admission rates were twice as high for those younger than 5 years at index burn (IRR, 95% CI 2.06, 1.54-2.74), three times higher for those 5-9 years and 15-18 years (IRR, 95% CI: 3.21, 1.92-5.37 and 3.37, 2.13-5.33, respectively) and almost five times higher for those aged 10-14 (IRR, 95% CI: 4.90, 3.10-7.76), when compared with respective ages of uninjured children. The burn cohort had higher admission rates for mood and anxiety disorders (IRR, 95% CI: 2.79, 2.20-3.53), psychotic disorders (IRR, 95% CI: 2.82, 1.97-4.03) and mental and behavioural conditions relating to drug and alcohol abuse (IRR, 95% CI: 4.25, 3.39-5.32).

Conclusions

Ongoing MH support is indicated for paediatric burn patients for a prolonged period after discharge to potentially prevent psychiatric morbidity and associated academic, social and psychological issues.

A retrospective cohort study to compare post-injury admissions for infectious diseases in burn patients, non-burn trauma patients and uninjured people

Background

Injury triggers a range of systemic effects including inflammation and immune responses. This study aimed to compare infectious disease admissions after burn and other types of injury using linked hospital admissions data.

Methods

A retrospective longitudinal study using linked health data of all patients admitted with burns in Western Australia (n = 30,997), 1980–2012, and age and gender frequency matched cohorts of people with non-burn trauma (n = 28,647) and no injury admissions (n = 123,399). Analyses included direct standardisation, negative binomial regression and Cox proportional hazards regression.

Results

Annual age-standardised infectious disease admission rates were highest for the burn cohort, followed by the non-burn trauma and uninjured cohorts. Age-standardised admission rates by decade showed different patterns across major categories of infectious diseases, with the lower respiratory and skin and soft tissue infections the most common for those with burns and other open trauma. Compared with the uninjured, those with burns had twice the admission rate for infectious disease after discharge (incident rate ratio (IRR), 95% confidence interval (CI): 2.04, 1.98–2.11) while non-burn trauma experienced 1.74 times higher rates (95%CI: 1.68–1.81). The burn cohort experienced 10% higher rates of first-time admissions after discharge when compared with the non-burn trauma (hazard ratio (HR), 95%CI: 1.10, 1.05–1.15). Compared with the uninjured cohort, incident admissions were highest during the first 30 days after discharge for burns (HR, 95%CI: 5.18, 4.15–6.48) and non-burn trauma (HR, 95%CI: 5.06, 4.03–6.34). While incident rates remained high over the study period, the magnitude decreased with increasing time from discharge: burn vs uninjured: HR, 95%CI: 30 days to 1 year: 1.69, 1.53–1.87; 1 to 10 years: 1.40, 1.33–1.47; 10 years to end of study period: 1.16, 1.08–1.24; non-burn trauma vs uninjured: HR, 95%CI: 30 days to 1 year: 1.71, 1.55–1.90; 1 to 10 years: 1.30, 1.24–1.37; 10 years to end of study period: 1.09, 1.03–1.17).

Conclusions

Burns and non-burn trauma patients had higher admission rates for infectious diseases compared with age and gender matched uninjured people. The pattern of annual admission rates for major categories of infectious diseases varied across injury groups. Overall, the burn cohort experienced the highest rates for digestive, lower respiratory and skin and soft tissue infections. These results suggest long-term vulnerability to infectious disease after injury, possibly related to long-term immune dysfunction.