Streptococcus pneumoniae-associated hemolytic uremic syndrome

Bronchopleural fistula management in a pediatric patient requiring extracorporeal membrane oxygenation

Bronchopleural fistula (BPF) is a connection between the bronchus and pleural cavity. It is associated with high morbidity and mortality and management of BPF has not been well described in the pediatric population. We describe a 2-year-old girl who presented with fever and increased work of breathing, found to have atypical hemolytic uremic syndrome and Streptococcus necrotizing pneumonia with development of persistent air leak due to bronchopleural fistulas requiring extracorporeal membrane oxygenation (ECMO). Three endobronchial valves were placed with successful resolution of bronchopleural fistulas. She required tracheostomy for chronic respiratory failure and endobronchial valves were eventually removed. Approximately 3.5 months after discharge to acute care rehabilitation, tracheostomy was successfully decannulated. This case highlights the successful use of endobronchial valves for resolution of BPF while on ECMO as well as the importance of further studies on optimal candidates, timing and duration of intervention in addition to sequelae of endobronchial valve placement.

The Role of the Complement System in the Pathogenesis of Infectious Forms of Hemolytic Uremic Syndrome

Hemolytic uremic syndrome (HUS) is an acute disease and the most common cause of childhood acute renal failure. HUS is characterized by a triad of symptoms: microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. In most of the cases, HUS occurs as a result of infection caused by Shiga toxin-producing microbes: hemorrhagic Escherichia coli and Shigella dysenteriae type 1. They account for up to 90% of all cases of HUS. The remaining 10% of cases grouped under the general term atypical HUS represent a heterogeneous group of diseases with similar clinical signs. Emerging evidence suggests that in addition to E. coli and S. dysenteriae type 1, a variety of bacterial and viral infections can cause the development of HUS. In particular, infectious diseases act as the main cause of aHUS recurrence. The pathogenesis of most cases of atypical HUS is based on congenital or acquired defects of complement system. This review presents summarized data from recent studies, suggesting that complement dysregulation is a key pathogenetic factor in various types of infection-induced HUS. Separate links in the complement system are considered, the damage of which during bacterial and viral infections can lead to complement hyperactivation following by microvascular endothelial injury and development of acute renal failure.

The role of pneumococcal extracellular vesicles on the pathophysiology of the kidney disease hemolytic uremic syndrome

Streptococcus pneumoniae-induced hemolytic uremic syndrome (Sp-HUS) is a kidney disease characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. This disease is frequently underdiagnosed and its pathophysiology is poorly understood. In this work, we compared clinical strains, isolated from infant Sp-HUS patients, with a reference pathogenic strain D39, for host cytotoxicity and further explored the role of Sp-derived extracellular vesicles (EVs) in the pathogenesis of an HUS infection. In comparison with the wild-type strain, pneumococcal HUS strains caused significant lysis of human erythrocytes and increased the release of hydrogen peroxide. Isolated Sp-HUS EVs were characterized by performing dynamic light-scattering microscopy and proteomic analysis. Sp-HUS strain released EVs at a constant concentration during growth, yet the size of the EVs varied and several subpopulations emerged at later time points. The cargo of the Sp-HUS EVs included several virulence factors at high abundance, i.e., the ribosomal subunit assembly factor BipA, the pneumococcal surface protein A, the lytic enzyme LytC, several sugar utilization, and fatty acid synthesis proteins. Sp-HUS EVs strongly downregulated the expression of the endothelial surface marker platelet endothelial cell adhesion molecule-1 and were internalized by human endothelial cells. Sp-HUS EVs elicited the release of pro-inflammatory cytokines (interleukin [IL]-1β, IL-6) and chemokines (CCL2, CCL3, CXCL1) by human monocytes. These findings shed new light on the overall function of Sp-EVs, in the scope of infection-mediated HUS, and suggest new avenues of research for exploring the usefulness of Sp-EVs as therapeutic and diagnostic targets. IMPORTANCE Streptococcus pneumoniae-associated hemolytic uremic syndrome (Sp-HUS) is a serious and underdiagnosed deadly complication of invasive pneumococcal disease. Despite the introduction of the pneumococcal vaccine, cases of Sp-HUS continue to emerge, especially in children under the age of 2. While a lot has been studied regarding pneumococcal proteins and their role on Sp-HUS pathophysiology, little is known about the role of extracellular vesicles (EVs). In our work, we isolate and initially characterize EVs from a reference pathogenic strain (D39) and a strain isolated from a 2-year-old patient suffering from Sp-HUS. We demonstrate that despite lacking cytotoxicity toward human cells, Sp-HUS EVs are highly internalized by endothelial cells and can trigger cytokine and chemokine production in monocytes. In addition, this work specifically highlights the distinct morphological characteristics of Sp-HUS EVs and their unique cargo. Overall, this work sheds new light into potentially relevant players contained in EVs that might elucidate about pneumococcal EVs biogenesis or pose as interesting candidates for vaccine design.

Acute organ injury and long-term sequelae of severe pneumococcal infections

Streptococcus pneumoniae (Spn) is a major public health problem, as it is a main cause of otitis media, community-acquired pneumonia, bacteremia, sepsis, and meningitis. Acute episodes of pneumococcal disease have been demonstrated to cause organ damage with lingering negative consequences. Cytotoxic products released by the bacterium, biomechanical and physiological stress resulting from infection, and the corresponding inflammatory response together contribute to organ damage accrued during infection. The collective result of this damage can be acutely life-threatening, but among survivors, it also contributes to the long-lasting sequelae of pneumococcal disease. These include the development of new morbidities or exacerbation of pre-existing conditions such as COPD, heart disease, and neurological impairments. Currently, pneumonia is ranked as the 9^th leading cause of death, but this estimate only considers short-term mortality and likely underestimates the true long-term impact of disease. Herein, we review the data that indicates damage incurred during acute pneumococcal infection can result in long-term sequelae which reduces quality of life and life expectancy among pneumococcal disease survivors.

Atypical Hemolytic Uremic Syndrome Secondary to Pancreatitis: A Case Report

This is a report of an extremely rare case of an atypical hemolytic uremic syndrome (aHUS) that appears to have been triggered by acute pancreatitis. A 68-year-old man was examined at a medical institution because of sudden lower abdominal pain. The patient was diagnosed with acute pancreatitis on computed tomography. Hemoglobinuria and laboratory findings indicative of intravascular hemolysis were noted. Biochemical analysis revealed normal results for von Willebrand factor activity, antiplatelet antibodies, and ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13), and stool culture was negative for Shiga-toxin-producing Escherichia coli, leading to the diagnosis of aHUS. Treatment for acute pancreatitis resulted in improvement in the laboratory findings, and the patient's progress was monitored without treatment intervention for aHUS. On day 2 of hospitalization, the abdominal symptoms and hemoglobinuria resolved without any subsequent recurrence. In the absence of any complications, the patient was transferred back to the initial hospital on day 26 of hospitalization. When hemolytic anemia or thrombocytopenia of unknown etiology is observed, aHUS should be suspected, and clinicians should be aware that acute pancreatitis may be a potential cause of aHUS.

Streptococcus Pneumoniae Bacteremia with Acute Kidney Injury and Transient ADAMTS13 Deficiency

A 43-year-old woman with a medical history of splenectomy for immune thrombocytopenic purpura was diagnosed with Streptococcus pneumoniae bacteremia. Her initial complaints were fever and more importantly painful extremities that appeared cyanotic. During her hospitalisation, she never developed cardiocirculatory failure but presented acute kidney injury (AKI) with oliguria. Laboratory investigations confirmed AKI with serum creatinine 2.55 mg/dL which peaked at 6.49 mg/dL. There was also evidence for disseminated intravascular coagulation (DIC) with decreased platelet count, low fibrinogen levels, and high D-dimer levels. There were no signs of haemolytic anaemia. The initial ADAMTS13 activity was low (17%) but slowly recovered. Renal function progressively improved with supportive therapy, as opposed to the progressing skin necrosis. The association of DIC and low ADAMTS13 activity may have contributed to the severity of microthrombotic complications, even in the absence of thrombotic microangiopathy as thrombotic thrombocytopenic purpura (TTP) or pneumococcal-associated haemolytic uremic syndrome (pa-HUS).

Hemolytic-Uremic Syndrome in Children

Hemolytic uremic syndrome is characterized by a triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney failure. Most cases are caused by Shiga-toxin-producing bacteria, especially Escherichia coli. Transmission occurs through ground beef and unpasteurized milk. STEC-HUS is the main cause of acute renal failure in children. Management remains supportive. Immediate outcome is most often. Atypical HUS represents about 5% of cases, has a relapsing course with more than half of the patients progressing to end-stage kidney failure. Most cases are due to variants in complement regulators of the alternative pathway. Complement inhibitors, such as eculizumab, have considerably improved the prognosis.

Haemolytic uraemic syndrome

Haemolytic uraemic syndrome (HUS) is a heterogeneous group of diseases that result in a common pathology, thrombotic microangiopathy, which is classically characterised by the triad of non-immune microangiopathic haemolytic anaemia, thrombocytopenia, and acute kidney injury. In this Seminar, different causes of HUS are discussed, the most common being Shiga toxin-producing Escherichia coli HUS. Identifying the underlying thrombotic microangiopathy trigger can be challenging but is imperative if patients are to receive personalised disease-specific treatment. The quintessential example is complement-mediated HUS, which once carried an extremely high mortality but is now treated with anti-complement therapies with excellent long-term outcomes. Unfortunately, the high cost of anti-complement therapies all but precludes their use in low-income countries. For many other forms of HUS, targeted therapies are yet to be identified.

A Case of Thrombotic Microangiopathy and Acute Sarcoidosis

Although sarcoidosis is an established cause of multiorgan dysfunction, acute presentation with thrombotic microangiopathy resulting in severe renal and hematological sequelae has not been reported. We describe the case of a patient presenting with hypercalcemia, pancreatitis, and acute renal failure, followed by microangiopathic hemolytic anemia. Although there were no significant respiratory symptoms, thoracic radiology and mediastinal lymph node biopsy results were in keeping with sarcoidosis as the underlying cause of this multisystem presentation. Corticosteroids were commenced with clinical and biochemical improvement. This novel case highlights the need to consider sarcoidosis as part of the differential diagnosis for unusual multiorgan presentations and for early multidisciplinary involvement in such cases to permit optimal treatment.

The association of anemia with the clinical outcomes of community-acquired pneumonia in children

OBJECTIVES

Anemia is associated with severe outcomes in adult community-acquired pneumonia (CAP), but few studies investigated its association with pediatric CAP. Hence, we tried to delineate the association of anemia with the clinical outcomes of CAP in children.

METHODS

This retrospective cohort study was conducted from 2010 to 2019 in a medical center. Inpatients aged 6 months to 17 years who were diagnosed with CAP and without major underlying diseases were included. The subjects' clinical data within 24 h of admission and clinical outcomes were collected. We accessed the rates of adverse outcomes and the adjusted odds ratios (ORs) of these outcomes between anemic and nonanemic patients, as well as among patients with different types of anemia.

RESULTS

In this study of 3601 patients, the prevalence of anemia was 11.6% (418/3601). Anemic patients had higher rates of intensive care (16.8% vs. 3.6%; p < 0.001), endotracheal intubation (11.0% vs. 1.3%; p < 0.001), and empyema (8.6% vs. 0.6%; p < 0.001) than nonanemic patients. In addition, anemia was independently associated with intensive care (adjusted OR, 3.00; 95% confidence interval [CI], 2.03-4.42), endotracheal intubation (adjusted OR, 3.79; 95% CI, 2.17-6.63), and empyema (adjusted OR, 4.72; 95% CI, 2.30-9.69). Iron-deficiency anemia (IDA) and normocytic anemia were associated with these adverse outcomes but not with anemia due to thalassemia trait.

CONCLUSION

Anemia is a biomarker associated with poor outcomes in pediatric CAP, and patients with IDA or normocytic anemia should be carefully monitored and managed since they may have higher disease severity.

Sialic acid and platelet count regulation: Implications in immune thrombocytopenia

Platelets are blood components that survive in circulation for 7 to 10 days in humans. Thus, platelet production by bone marrow (BM) megakaryocytes (MKs), and their removal from the blood circulation is precisely orchestrated to maintain an average platelet count. Abnormalities in both processes can result in thrombocytopenia (low platelet count) or thrombocytosis (high platelet count), often associated with the risk of bleeding or overt thrombus formation, respectively. Platelet glycans, particularly sialic acids, are indicators of platelet count. Loss of platelet sialic acids leads to platelet clearance. A State-of-the-Art lecture titled "Platelet and Megakaryocyte Glycobiology" was presented at the ISTH virtual congress 2021 to discuss (i) the loss of O-glycan sialic acid on BM MKs, revealing the Thomsen-Friedenreich (TF) antigen as a new concept of thrombocytopenia; herein, impaired thrombopoiesis is attributed to activation of immune cells with a plasmacytoid dendritic cell signature; and (ii) upregulation of antibodies against the TF antigen in pediatric patients with immune thrombocytopenia (ITP), positing that glycan alterations such as MK asialylation can lead to immune cell responses. Here, we discuss our findings alongside new data presented at the 2020 and 2021 ISTH congresses on the role of sialic acids and glycans in regulating platelet count. Desialylation is a prominent feature in thrombocytopenia, notably in ITP presentation. We compare similarities between ITP mediated with shear-stress and with storage-related asialylation. We also discuss genes involved in sialic acid synthesis leading to thrombocytopenia. Increased awareness in gene-regulating MK and platelet glycans is a giant leap to understanding the underpinning mechanisms of ITP and other forms of thrombocytopenia.

Immune cells surveil aberrantly sialylated O-glycans on megakaryocytes to regulate platelet count

Immune thrombocytopenia (ITP) is a platelet disorder. Pediatric and adult ITP have been associated with sialic acid alterations, but the pathophysiology of ITP remains elusive, and ITP is often a diagnosis of exclusion. Our analysis of pediatric ITP plasma samples showed increased anti-Thomsen-Friedenreich antigen (TF antigen) antibody representation, suggesting increased exposure of the typically sialylated and cryptic TF antigen in these patients. The O-glycan sialyltransferase St3gal1 adds sialic acid specifically on the TF antigen. To understand if TF antigen exposure associates with thrombocytopenia, we generated a mouse model with targeted deletion of St3gal1 in megakaryocytes (MK) (St3gal1MK-/-). TF antigen exposure was restricted to MKs and resulted in thrombocytopenia. Deletion of Jak3 in St3gal1MK-/- mice normalized platelet counts implicating involvement of immune cells. Interferon-producing Siglec H-positive bone marrow (BM) immune cells engaged with O-glycan sialic acid moieties to regulate type I interferon secretion and platelet release (thrombopoiesis), as evidenced by partially normalized platelet count following inhibition of interferon and Siglec H receptors. Single-cell RNA-sequencing determined that TF antigen exposure by MKs primed St3gal1MK-/- BM immune cells to release type I interferon. Single-cell RNA-sequencing further revealed a new population of immune cells with a plasmacytoid dendritic cell-like signature and concomitant upregulation of the immunoglobulin rearrangement gene transcripts Igkc and Ighm, suggesting additional immune regulatory mechanisms. Thus, aberrant TF antigen moieties, often found in pathological conditions, regulate immune cells and thrombopoiesis in the BM, leading to reduced platelet count.

Streptococcal pneumonia-associated hemolytic uremic syndrome treated by T-antibody-negative plasma exchange in children: Two case reports

BACKGROUND

The occurrence of Streptococcus pneumoniae-associated hemolytic uremic syndrome (SP-HUS) is increasing. Thomsen-Friedenreich antigen activation is highly involved in the pathogenesis of SP-HUS, and T-antibody-negative plasma exchange (PE) may be effective in the treatment of severe cases of SP-HUS.

CASE SUMMARY

We retrospectively reviewed two pediatric patients with SP-HUS. Both clinical features and laboratory examination results of the children were described. T-antibody-negative PE was performed in both cases. Both children made a full recovery after repeated PE and remained well at a 2 year follow-up.

CONCLUSION

Streptococcal pneumonia continues to be an uncommon but important cause of HUS. The successful treatment of the presented cases suggests that T-antibody-negative PE may benefit patients with SP-HUS.

Streptococcus Pneumoniae-Associated Hemolytic Uremic Syndrome in the Era of Pneumococcal Vaccine

Streptococcus pneumoniae-associated hemolytic uremic syndrome (Sp-HUS) is a serious complication of invasive pneumococcal disease that is associated with increased mortality in the acute phase and morbidity in the long term. Recently, Sp-HUS definition has undergone revision and cases are categorized as definite, probable, and possible, based on less invasive serological investigations that evaluate Thomsen-Friedenreich crypt antigen (T-antigen) activation. In comparison to the pre-vaccine era, Sp-HUS incidence seems to be decreasing after the introduction of 7-serotype valence and 13-serotype valence pneumococcal vaccines in 2000 and 2010, respectively. However, Sp-HUS cases continue to occur secondary to vaccine failure and emergence of non-vaccine/replacement serotypes. No single hypothesis elucidates the molecular basis for Sp-HUS occurrence, although pneumococcal neuraminidase production and formation of T-antigen antibody complexes on susceptible endothelial and red blood cells continues to remain the most acceptable explanation. Management of Sp-HUS patients remains supportive in nature and better outcomes are being reported secondary to earlier recognition, better diagnostic tools and improved medical care. Recently, the addition of eculizumab therapy in the management of Sp-HUS for control of dysregulated complement activity has demonstrated good outcomes, although randomized clinical trials are awaited. A sustained pneumococcal vaccination program and vigilance for replacement serotypes will be the key for persistent reduction in Sp-HUS cases worldwide.

Complement activation in children with Streptococcus pneumoniae associated hemolytic uremic syndrome

BACKGROUND

Hemolytic uremic syndrome caused by invasive pneumococcal disease (P-HUS) is rare in children and adolescents, but accompanied by high mortality in the acute phase and complicated by long-term renal sequelae. Abnormalities in the alternative complement pathway may additionally be contributing to the course of the disease but also to putative treatment options.

METHODS

Retrospective study to assess clinical course and laboratory data of the acute phase and outcome of children with P-HUS.

RESULTS

We report on seven children (median age 12 months, range 3-28 months) diagnosed with P-HUS. Primary organ manifestation was meningitis in four and pneumonia in three patients. All patients required dialysis which could be discontinued in five of them after a median of 25 days. In two patients, broad functional and genetic complement analysis was performed and revealed alternative pathway activation and risk haplotypes in both. Three patients were treated with the complement C5 inhibitor eculizumab. During a median follow-up time of 11.3 years, one patient died due to infectious complications after transplantation. Two patients showed no signs of renal sequelae.

CONCLUSIONS

Although pathophysiology in P-HUS remains as yet incompletely understood, disordered complement regulation seems to provide a clue to additional insights for pathology, diagnosis, and even targeted treatment.

Pediatric Pneumococcal Hemolytic Uremic Syndrome Treated with Sequence Tandem Therapeutic Plasma Exchange and Continuous Venovenous Hemodiafiltration: A Case Report

Hemolytic uremic syndrome (HUS) is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. Approximately 5% of HUS cases are associated with Streptococcus pneumoniae infections (pHUS). Treatment includes supportive care with appropriate antimicrobial therapy, fluid and blood product resuscitation, and renal replacement therapy. We presented a case of a 22-month-old previously healthy girl, who was hospitalized at University Hospital of Split. Left-sided pneumonia and sepsis caused by S. pneumoniae were confirmed. The course of illness was complicated with development of pHUS. Since the pathogenesis of pHUS is only partially understood, the treatment remains controversial. Our patient was successfully treated with daily sequence tandem continuous venovenous hemodiafiltration and therapeutic plasma exchange with albumins, along with other supportive measures. Therefore, in our opinion, plasmapheresis should be considered as a part of standard treatment of children with pHUS. Additionally, the incidence of pHUS appears to be increasing. S. pneumoniae is a particularly important among pediatric pathogens and it can cause wide spectrum of illnesses. Therefore, due to the significant burden of invasive pneumococcal disease, pneumococcal vaccination should be encouraged.

Plasma exchange and thrombotic microangiopathies: From pathophysiology to clinical practice

Thrombotic microangiopathy (TMA) brings together many diseases that have a commonality in the apparition of mechanical hemolysis with consuming thrombopenia. In all cases, these diseases can be life threatening, thereby justifying the implementation of treatment as an emergency. First-line treatment represents plasma exchange. This treatment has proven efficiency in improving the vital patient's and functional prognosis. However, the administration methods of plasma exchange can be redefined in light of the understanding of the pathophysiology of TMA. The aim of this review is to try to define, from pathophysiology, the place of plasma exchanges in the modern therapeutic arsenal of TMA.

Invasive Streptococcus Pneumoniae Septicemia Complicated with Hemolytic Uremic Syndrome and Meningitis

Streptococcus pneumoniae-associated hemolytic uremic syndrome (SpHUS) is an uncommon cause of hemolytic uremic syndrome (HUS). The diagnosis and treatment of Streptococcus pneumoniae-associated HUS is often difficult and associated with high long-term morbidity and mortality. The authors report a five-year-old child who developed HUS following an invasive Streptococcus (S.) pneumoniae infection. The child initially presented with fever, cough, and difficulty in breathing for three days duration and was clinically and radiologically diagnosed as having right middle lobe pneumonia. Blood culture grew Streptococcus pneumoniae. The cerebrospinal fluid analysis also showed Streptococcus pneumoniae. He was initially treated with intravenous cefotaxime. As the child had a poor response to cefotaxime with ongoing fever, antibiotics were changed to ceftriaxone and vancomycin. Although fever started to subside subsequently, the child deteriorated with reduced urine output and developed generalized body swelling. The hematological and biochemical evaluation confirmed hemolytic uremic syndrome. He needed continuous renal replacement therapy for five days and antibiotics were given for 14 days. He had no long-term sequelae on follow-up.

New insights into the pathogenesis of Streptococcus pneumoniae-associated hemolytic uremic syndrome

The purpose of this review is to describe Streptococcus pneumoniae-associated hemolytic uremic syndrome (P-HUS) with emphasis on new insights into the pathophysiology and management over the past 10 years. Even though awareness of this clinico-pathological entity has increased, it likely remains under-recognized. Recent observations indicate that although neuraminidase activity and exposure of the T-antigen are necessary for development of P-HUS, they are not sufficient; activation of the alternate pathway of complement may also contribute. It is unclear, however, whether or not eculizumab and/or plasmapheresis are of value.

Typical and Atypical Hemolytic Uremic Syndrome in the Critically Ill

Hemolytic uremic syndrome is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. Disseminated intravascular coagulation, thrombotic thrombocytopenic purpura, and hemolytic uremic syndrome have a similar clinical presentation. Diagnostic needs to be prompt to decrease mortality, because identifying the different disorders can help to tailor specific, effective therapies. However, diagnosis is challenging and morbidity and mortality remain high, especially in the critically ill population. Development of clinical prediction scores and rapid diagnostic tests for hemolytic uremic syndrome based on mechanistic knowledge are needed to facilitate early diagnosis and assign timely specific treatments to patients with hemolytic uremic syndrome variants.

HEMOLYTIC UREMIC SYNDROME ASSOCIATED WITH STREPTOCOCCUS PNEUMONIAE IN PEDIATRICS: A CASE SERIES

Objective:

To describe a case series of four (4) patients with hemolytic uremic syndrome due to Streptococcus pneumoniae in a level four complexity institution in the city of Bogotá, D.C., Colombia.

Cases description:

We describe cases of four patients who presented respiratory symptoms and fever. All four patients were in regular conditions on hospital admission, after which they required intensive care and ventilatory support. Upon admission, three cases showed evidence of pleuropulmonary complication. Penicillin-sensitive Streptococcus pneumoniae was isolated in all cases. All patients presented anemia, severe thrombocytopenia, schistocytes on peripheral blood smear, and hyperazotemia. They required blood transfusion and renal replacement therapy during their hospitalization. The patients were diagnosed with hemolytic uremic syndrome due to S. pneumoniae. Three of the four patients had a progressive recovery of the renal function and were discharged after an average of 36 days of hospital stay. The remaining patient had two amputations in the extremities due to thrombotic vascular complications and was discharged after 99 days of hospital stay, requiring hemodialysis every other day.

Comments:

Hemolytic uremic syndrome due to Streptococcus pneumoniae is a rare but severe complication of invasive pneumococcal disease. Complicated pneumonia is the main condition associated with this entity. It is noteworthy the short period in which these cases were presented, considering the low annual incidence of the disease.

Streptococcus pneumoniae From Patients With Hemolytic Uremic Syndrome Binds Human Plasminogen via the Surface Protein PspC and Uses Plasmin to Damage Human Endothelial Cells

Pneumococcal hemolytic uremic syndrome (HUS) in children is caused by infections with Streptococcus pneumoniae. Because endothelial cell damage is a hallmark of HUS, we studied how HUS-inducing pneumococci derived from infant HUS patients during the acute phase disrupt the endothelial layer. HUS pneumococci efficiently bound human plasminogen. These clinical isolates of HUS pneumococci efficiently bound human plasminogen via the bacterial surface proteins Tuf and PspC. When activated to plasmin at the bacterial surface, the active protease degraded fibrinogen and cleaved C3b. Here, we show that PspC is a pneumococcal plasminogen receptor and that plasmin generated on the surface of HUS pneumococci damages endothelial cells, causing endothelial retraction and exposure of the underlying matrix. Thus, HUS pneumococci damage endothelial cells in the blood vessels and disturb local complement homeostasis. Thereby, HUS pneumococci promote a thrombogenic state that drives HUS pathology.

Hemolytic Uremic Syndrome Associated With Non-Shigatoxin-producing Infectious Agents: Expanding the Shigatoxin Theory

Diarrhea-associated hemolytic uremic syndrome (HUS) is usually associated with shigatoxin-producing Escherichia coli or shigella infections. We report 2 cases of HUS, respectively, caused by salmonella and Campylobacter jejuni infections. None of these bacteria produce shigatoxins, and the underlying mechanism of HUS development remains unknown. In streptococcus pneumoniae-associated HUS, bacterial neuraminidase cleaves neuraminic acid and causes exposure of Thomsen-Friedenreich cryptantigen on the cell surface of, for example, erythrocytes, which induces an inflammatory response caused by binding of preformed IgM. Both campylobacter and salmonella bacteria also produce neuraminidase, and HUS development could be explained by a similar mechanism.

Hemolytic Uremic Syndrome

Hemolytic uremic syndrome (HUS) is the clinical triad of thrombocytopenia, anemia, and acute kidney injury. Classically associated with enterocolitis from Shiga toxin-producing Escherichia coli, HUS is also associated with Streptococcus pneumoniae infections; genetic dysregulation of the alternative complement pathway or coagulation cascade; and, rarely, a hereditary disorder of cobalamin C metabolism. These share a common final pathway of a prothrombotic and proinflammatory state on the endothelial cell surface, with fibrin and platelet deposition. Much work has been done to distinguish between the different mechanisms of disease, thereby informing the optimal therapeutic interventions for each entity.

Commentary: Campylobacter and Hemolytic Uremic Syndrome

There are reports in the literature stating that Campylobacter infections can cause hemolytic uremic syndrome (HUS); however, a mechanism for how Campylobacter induces HUS has not been proposed by investigators. The most common bacterial inducer of HUS is the Shiga toxin-producing Escherichia coli (STEC), and a few cases of HUS are induced by an invasive Shigella dysenteriae or Streptococcus pneumoniae infection. Campylobacter spp. have not been shown to produce Shiga toxin (Stx) nor do they possess genetic elements capable of producing a Stx-like toxin. The neuraminidase associated with pneumococcal HUS has not been observed in Campylobacter. Therefore, in the absence of a well-defined toxic mechanism, it not clear that Campylobacter actually causes HUS.

Pneumococcal haemolytic uraemic syndrome in the postvaccine era

OBJECTIVE

Pneumococcal infection is a leading cause of haemolytic uraemic syndrome (HUS) and is potentially vaccine preventable. Published data suggest high mortality and poor renal outcomes. The introduction of the 7-valent pneumococcal conjugate vaccine (PCV) has seen the emergence of disease caused by non-vaccine strains, particularly 19A. We sought to describe serotype prevalence and outcomes, particularly after the introduction of the 13-valent PCV.

DESIGN AND SETTING

We performed a retrospective chart review, using hospital medical records to identify cases of HUS in a tertiary paediatric hospital in Australia over a 20-year period (January 1997-December 2016). Associated pneumococcal infection was identified, and serotype data were categorised according to vaccine era: prevaccine (January 1997-December 2004), PCV7 (January 2005-June 2011) and PCV13 (July 2011-December 2016).

RESULTS

We identified 66 cases of HUS. Pneumococcal infection was proven in 11 cases, representing 4% (1/26) of cases prior to the introduction of PCV7, 20% (3/15) in the PCV7 era and 28% (7/25) in the PCV13 era. Subtype 19A was the most prevalent pneumococcal serotype (6/11). All four patients who received PCV7 were infected with a non-vaccine serotype. Four of the five patients who received PCV13 were classed as vaccine failures. Median follow-up was 14 (range 1-108) months. Chronic kidney disease was the most common complication (4/7). We observed no mortality, neurological sequelae or progression to end-stage kidney disease.

CONCLUSIONS

Serotype 19A is most commonly associated with pneumococcal HUS, despite the introduction of the 13-valent vaccine. Chronic kidney disease is a significant complication of pneumococcal HUS.

Successful treatment of a Streptococcus pneumoniae-associated haemolytic uraemic syndrome by eculizumab

Haemolytic uraemic syndrome (HUS) is a rare complication of invasive infection by Streptococcus pneumoniae (SP-HUS), especially in adults. Here we report an unusual case of a 53-year-old man presenting SP-HUS with severe multivisceral involvement. After failure of supportive care and plasma exchanges, eculizumab (anti-C5 antibody) resulted in a favourable outcome.

Treatment and management of children with haemolytic uraemic syndrome

Haemolytic uraemic syndrome (HUS), comprising microangiopathic haemolytic anaemia, thrombocytopaenia and acute kidney injury, remains the leading cause of paediatric intrinsic acute kidney injury, with peak incidence in children aged under 5 years. HUS most commonly occurs following infection with Shiga toxin-producing Escherichia coli (STEC-HUS). Additionally, HUS can occur as a result of inherited or acquired dysregulation of the alternative complement cascade (atypical HUS or aHUS) and in the setting of invasive pneumococcal infection. The field of HUS has been transformed by the discovery of the central role of complement in aHUS and the dawn of therapeutic complement inhibition. Herein, we address these three major forms of HUS in children, review the latest evidence for their treatment and discuss the management of STEC infection from presentation with bloody diarrhoea, through to development of fulminant HUS.

Influenza-associated thrombotic microangiopathies

Thrombotic microangiopathy (TMA) refers to phenotypically similar disorders, including hemolytic uremic syndromes (HUS) and thrombotic thrombocytopenic purpura (TTP). This review explores the role of the influenza virus as trigger of HUS or TTP. We conducted a literature survey in PubMed and Google Scholar using HUS, TTP, TMA, and influenza as keywords, and extracted and analyzed reported epidemiological and clinical data. We identified 25 cases of influenza-associated TMA. Five additional cases were linked to influenza vaccination and analyzed separately. Influenza A was found in 83%, 10 out of 25 during the 2009 A(H1N1) pandemic. Two patients had bona fide TTP with ADAMTS13 activity <10%. Median age was 15 years (range 0.5-68 years), two thirds were male. Oligoanuria was documented in 81% and neurological involvement in 40% of patients. Serum C3 was reduced in 5 out of 14 patients (36%); Coombs test was negative in 7 out of 7 and elevated fibrin/fibrinogen degradation products were documented in 6 out of 8 patients. Pathogenic complement gene mutations were found in 7 out of 8 patients tested (C3, MCP, or MCP combined with CFB or clusterin). Twenty out of 24 patients recovered completely, but 3 died (12%). Ten of the surviving patients underwent plasma exchange (PLEX) therapy, 5 plasma infusions. Influenza-mediated HUS or TTP is rare. A sizable proportion of tested patients demonstrated mutations associated with alternative pathway of complement dysregulation that was uncovered by this infection. Further research is warranted targeting the roles of viral neuraminidase, enhanced virus-induced complement activation and/or ADAMTS13 antibodies, and rational treatment approaches.

Defining the role of pneumococcal neuraminidases and O-glycosidase in pneumococcal haemolytic uraemic syndrome

The host and bacterial factors that lead to development of pneumococcal haemolytic uraemic syndrome (pHUS) remain poorly defined; however, it is widely believed that pneumococcal exposure of the Thomsen-Friedenreich antigen (T-antigen) on host surfaces is a key step in pathogenesis. Two enzymatic activities encoded by pneumococci determine the level of T-antigen exposed. Neuraminidases cleave terminal sialic acid to expose the T-antigen which is subsequently cleaved by O-glycosidase Eng. While a handful of studies have examined the role of neuraminidases in T-antigen exposure, no studies have addressed the potential role of O-glycosidase. This study used 29 pHUS isolates from the USA and 31 serotype-matched controls. All isolates contained eng, and no significant correlation between enzymatic activity and disease state (pHUS and blood non-pHUS isolates) was observed. A prior study from Taiwan suggested that neuraminidase NanC contributes to the development of pHUS. However, we observed no difference in nanC distribution. Similar to previously published data, we found no significant correlation between neuraminidase activity and disease state. Accurate quantification of these enzymatic activities from bacteria grown in whole blood is currently impossible, but we confirmed that there were no significant correlations between disease state and neuraminidase and O-glycosidase transcript levels after incubation in blood. Genomic sequencing of six pHUS isolates did not identify any genetic elements possibly contributing to haemolytic uraemic syndrome. These findings support the hypothesis that while exposure of T-antigen may be an important step in disease pathogenesis, host factors likely play a substantial role in determining which individuals develop haemolytic uraemic syndrome after pneumococcal invasive disease.

Health-related quality of life and mental health in parents of children with hemolytic uremic syndrome

BACKGROUND

Little is known about health-related quality of life (HRQoL) and mental health of parents having children with a history of hemolytic uremic syndrome (HUS).

METHODS

This study included 63 mothers and 58 fathers of a cohort of 63 HUS-affected children. At assessment, the mean time since a child experienced an acute episode of HUS was 6.4 years. Parental HRQoL, mental health and posttraumatic stress disorder (PTSD) were assessed with standardized self-report questionnaires. Medical data were extracted from patients' hospital records.

RESULTS

The HRQoL and mental health of both the mothers and fathers were not impaired compared to normative data. However, a shorter time since a child's acute HUS episode was a significant predictor of lower HRQoL among the mothers, while no such effect was found among the fathers. Two fathers (3%), but no mothers, met the criteria for a diagnosis of HUS-related full PTSD; one father (2%) and four mothers (6%) met the criteria for a diagnosis of HUS-related partial PTSD.

CONCLUSIONS

Our study shows that most parents of our study sample were doing well in terms of HRQoL and mental health, although a small number met the criteria for full or partial PTSD diagnosis due to their child's HUS. We therefore recommend that healthcare providers pay special attention to parents regarding PTSD symptoms during the clinical follow-up of a HUS-affected child since some parents may benefit from psychological support.

Pneumococcal hemolytic uremic syndrome and steroid resistant nephrotic syndrome

Pneumococcal-associated hemolytic uremic syndrome (pHUS) is a rare but severe complication of invasive Streptococcus pneumoniae infection. We report the case of a 12-year-old female with steroid-resistant nephrotic syndrome treated with adrenocorticotrophic hormone (H.P. Acthar(®) Gel), who developed pneumococcal pneumonia and subsequent pHUS. While nephrotic syndrome is a well-known risk factor for invasive pneumococcal disease, this is the first reported case of pHUS in an adolescent patient with nephrotic syndrome, and reveals novel challenges in the diagnosis, treatment and potential prevention of this complication.

Infectious Diseases and the Kidney in Children

The kidney is involved in a wide range of bacterial, viral, fungal, and parasitic diseases. In most systemic infections, renal involvement is a minor component of the illness, but in some, renal failure may be the presenting feature and the major problem in management. Although individual infectious processes may have a predilection to involve the renal vasculature, glomeruli, interstitium, or collecting systems, a purely anatomic approach to the classification of infectious diseases affecting the kidney is rarely helpful because most infections may involve several different aspects of renal function. In this chapter, a microbiological classification of the organisms affecting the kidney is adopted. Although they are important causes of renal dysfunction in infectious diseases, urinary tract infections and hemolytic uremic syndrome (HUS) are not discussed in detail because they are considered separately in chapters XX and XX, respectively.

Neurodevelopmental long-term outcome in children after hemolytic uremic syndrome

BACKGROUND

To investigate the long-term neurodevelopmental outcome in children after hemolytic uremic syndrome (HUS) and to compare outcome dependent on central nervous system (CNS) involvement during HUS.

METHODS

A single-center retrospective cohort of 47 children was examined at a median age of 10.6 (range 6-16.9) years and a median follow-up of 7.8 (range 0.4-15.3) years after having had HUS. Intellectual performance was assessed with the German version of the Wechsler Intelligence Scale 4th version and neuromotor performance with the Zurich Neuromotor Assessment (ZNA). The occurrence of neurological symptoms during the acute phase of HUS was evaluated retrospectively.

RESULTS

Mean IQ of the whole study population fell within the normal range (median full scale IQ 104, range 54-127). Neuromotor performance was significantly poorer in the domains "adaptive fine," "gross motor," "static balance" (all p < 0.05) and "associated movements" (p < 0.001); only the "pure motor" domain was within the normal reference range. Neurological findings occurred in 16/47 patients (34 %) during acute HUS. Neurodevelopmental outcome was not significantly different between children with or without CNS involvement.

CONCLUSIONS

Our follow-up of children after HUS showed a favorable cognitive outcome. However, neuromotor outcome was impaired in all study participants. Neurological impairment during acute HUS was not predictive of outcome.

Complement, thrombotic microangiopathy and disseminated intravascular coagulation

In the blurring boundaries between clinical practice and scientific observations, it is increasingly attractive to propose shared disease mechanisms that could explain clinical experience. With the advent of available therapeutic options for complement inhibition, there is a push for more widespread application in patients, despite a lack of clinically relevant research. Patients with disseminated intravascular coagulation (DIC) and thrombotic microangiopathies (TMA) frequently exhibit complement activation and share the clinical consequences of thrombocytopenia, microangiopathic hemolytic anemia, and microvascular thrombosis. However, they arise from very different molecular etiologies giving rise to cautious questions about inclusive treatment approaches because most clinical observations are associative and not cause-and-effect. Complement inhibition is successful in many cases of atypical hemolytic uremic syndrome, greatly reducing morbidity and mortality of patients by minimizing thrombocytopenia, microangiopathic hemolytic anemia, and microvascular thrombosis. But is this success due to targeting disease etiology or because complement is a sufficiently systemic target or both? These questions are important because complement activation and similar clinical features also are observed in many DIC patients, and there are mounting calls for systemic inhibition of complement mediators despite the enormous differences in the primary diseases complicated by DIC. We are in great need of thoughtful and standardized assessment with respect to both beneficial and potentially harmful consequences of complement activation in these patient populations. In this review, we discuss about what needs to be done in terms of establishing the strategy for complement inhibition in TMA and DIC, based on the current knowledge.

Red blood cell Thomsen-Friedenreich antigen expression and galectin-3 plasma concentrations in Streptococcus pneumoniae-associated hemolytic uremic syndrome and hemolytic anemia

BACKGROUND

Pneumococcal hemolytic uremic syndrome (P-HUS) is a rare but severe complication of invasive pneumococcal disease (IPD) in young children. Consensual biologic diagnosis criteria are currently lacking.

STUDY DESIGN AND METHODS

A prospective study was conducted on 10 children with culture-confirmed IPD. Five presented with full-blown P-HUS, three had an incomplete form with hemolytic anemia and mild or no uremia (P-HA), and two had neither HUS nor HA. Thomsen-Friedenreich (T), Th, and Tk cryptantigens and sialic acid expression were determined on red blood cells (RBCs) with peanut (PNA), Glycine soja (SBA), Bandeiraea simplicifolia II, and Maackia amurensis lectins. Plasma concentrations of the major endogenous T-antigen-binding protein, galectin-3 (Gal-3), were analyzed.

RESULTS

We found that RBCs strongly reacted with PNA and SBA lectins in all P-HUS and P-HA patients. Three P-HUS and three P-HA patients showed also concomitant Tk activation. Direct antiglobulin test (DAT) was positive in three P-HUS (one with anti-C3d and two with anti-IgG) and two P-HA patients (one with anti-C3d and one with anti-IgG). RBCs derived from the two uncomplicated IPD patients reacted with PNA but not with SBA lectin. Gal-3 plasma concentrations were increased in all P-HUS patients.

CONCLUSIONS

The results indicate high levels of neuraminidase activity and desialylation in both P-HUS and P-HA patients. T-antigen activation is more sensitive than DAT for P-HUS diagnosis. Combining PNA and SBA lectins is needed to improve the specificity of T-antigen activation. High concentrations of Gal-3 in P-HUS patients suggest that Gal-3 may contribute to the pathogenesis of P-HUS.

Management of hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) is a disease characterized by hemolysis, thrombocytopenia, and acute kidney injury, although other organs may be involved. Most cases are due to infection with Shiga toxin-producing Escherichia coli (STEC). Early identification and initiation of best supportive care, with microbiological input to identify the pathogen, result in a favorable outcome in most patients. The remaining 10% of HUS cases are classed together as atypical HUS and have a diverse etiology. The majority are due to inherited or acquired abnormalities that lead to a failure to control complement activation. Atypical HUS occurring in other situations (for example, related to pregnancy or kidney transplantation) may also involve excessive complement activation. Plasma therapies can reverse defective complement control, and it is now possible to specifically target complement activation. This has led to improved outcomes in patients with atypical forms of HUS. We will review our current understanding of the pathogenesis of HUS and how this has led to advances in patient care.

Structural basis for sialic acid-mediated self-recognition by complement factor H

The serum protein complement factor H (FH) ensures downregulation of the complement alternative pathway, a branch of innate immunity, upon interaction with specific glycans on host cell surfaces. Using ligand-based NMR, we screened a comprehensive set of sialylated glycans for binding to FH and solved the crystal structure of a ternary complex formed by the two C-terminal domains of FH, a sialylated trisaccharide and the complement C3b thioester-containing domain. Key residues in the sialic acid binding site are conserved from mice to men, and residues linked to atypical hemolytic uremic syndrome cluster within this binding site, suggesting a possible role for sialic acid as a host marker also in other mammals and a critical role in human renal complement homeostasis. Unexpectedly, the FH sialic acid binding site is structurally homologous to the binding sites of two evolutionarily unrelated proteins. The crystal structure also advances our understanding of bacterial immune evasion strategies.

Hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy defined by thrombocytopenia, nonimmune microangiopathic hemolytic anemia, and acute renal failure. The most frequent form is associated with infections by Shiga-like toxin-producing bacteria (STEC-HUS). Rarer cases are triggered by neuraminidase-producing Streptococcus pneumoniae (pneumococcal-HUS). The designation of aHUS is used to refer to those cases in which an infection by Shiga-like toxin-producing bacteria or S. pneumoniae can be excluded. Studies performed in the last two decades have documented that hyperactivation of the complement system is the pathogenetic effector mechanism leading to the endothelial damage and the microvascular thrombosis in aHUS. Recent data suggested the involvement of the complement system in the pathogenesis of STEC-HUS and pneumococcal-HUS as well. Clinical signs and symptoms may overlap among the different forms of HUS; however, pneumococcal-HUS and aHUS have a worse prognosis compared with STEC-HUS. Early diagnosis and identification of underlying pathogenetic mechanism allows instating specific support measures and therapies. In clinical trials in patients with aHUS, complement inhibition by eculizumab administration leads to a rapid and sustained normalization of hematological parameters with improvement in long-term renal function. This review summarizes current concepts about the epidemiological findings, the pathological and clinical aspects of STEC-HUS, pneumococcal-HUS, and aHUS, and their diagnosis and management.

Diagnosis of Streptococcus pneumoniae-associated hemolytic uremic syndrome

BACKGROUND

Hemolytic uremic syndrome related to pneumococcal infection (P+HUS) can be difficult to diagnose due to the lack of a specific test and the absence of a consensus for definite diagnostic criteria.

METHODS

A retrospective study was conducted on the cases that have been considered as P+HUS in the participating centers during the past 10 years. Diagnostic strategy and criteria used for the diagnosis of P+HUS were evaluated and compared with a review of literature data.

RESULTS

A total of 17 children were studied. Tests ruling out other causes of HUS were performed in 94% of cases. Direct confirmatory tests for P+HUS were done in a minority of cases as Thomsen-Friedenreich antigen testing using lectin assay were done in only 2 patients (11%). Retrospectively, the diagnosis of P+HUS was confirmed in 28% to 89% of cases depending on the already published criteria used. A literature review focused on the last 15 years confirmed these diagnostic difficulties due to variable definition criteria and bring a new light on the potential usefulness of tests used to reveal T activation in this setting.

CONCLUSION

To date, in a context of suspicion of P+HUS, no precise, practical and consensual strategy exists for T-antigen exposure diagnosis. The T-antigen activation test using peanut lectin might be the most appropriate test for a direct diagnosis of P+HUS. A large prospective study is required to confirm this hypothesis. However, before such data are available, its use could be of help when a suspicion of P+HUS is present given the therapeutic impact of such a diagnosis.

Haemolytic uraemic syndrome associated with Pseudomonas aeruginosa sepsis

Haemolytic uraemic syndrome (HUS) is a recognized complication of infection with Shiga toxin-producing Escherichia coli (STEC) and Shigella dysenteriae type 1. Infections with other micro-organisms, especially Streptococcus pneumoniae, have been cited as causes of HUS. In addition, influenza virus and other viruses may rarely be associated with this syndrome. A 2-year-old girl presented with severe Pseudomonas aeruginosa sepsis with renal failure and ecthyma gangrenosum. Further investigations revealed features of HUS. She was managed with antibiotics and other supportive measures including peritoneal dialysis, and subsequently made a full recovery. A possible role of neuraminidase in the pathogenesis of P. aeruginosa-associated HUS was proposed. This is the first reported case of P. aeruginosa sepsis leading to HUS.