Hemolytic uremic syndrome and streptococcus pneumoniae: improving our understanding

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.

Influenza-associated hemolytic uremic syndrome: The pathogenic role of the virus

A 3-year-old girl came to our attention for fever and upper respiratory tract infection associated with thrombocytopenia, non-immune hemolytic anemia, and acute kidney injury (AKI). Complete blood count and renal function slowly normalized, with no need for dialysis. She was always normotensive with valid diuresis; her neurological status also rapidly improved. Nasal swab turned out positive for influenza A H1N1; stool test was negative for Shiga toxin-producing Escherichia coli (STEC). The patient was treated with oseltamivir for 5 days with a favorable outcome. Association between hemolytic uremic syndrome (HUS) and H1N1 influenza is poorly reported in literature [1, 2, 3, 4]. The pathogenic role of the virus in causing HUS is still controversial and debated [1, 2, 3, 4]. In our patient, complement activity markers (serum C3 and C5b-9) alteration suggested a transient, virus-mediated complement activation.

Microvascular thrombosis: experimental and clinical implications

A significant amount of clinical and research interest in thrombosis is focused on large vessels (eg, stroke, myocardial infarction, deep venous thrombosis, etc.); however, thrombosis is often present in the microcirculation in a variety of significant human diseases, such as disseminated intravascular coagulation, thrombotic microangiopathy, sickle cell disease, and others. Further, microvascular thrombosis has recently been demonstrated in patients with COVID-19, and has been proposed to mediate the pathogenesis of organ injury in this disease. In many of these conditions, microvascular thrombosis is accompanied by inflammation, an association referred to as thromboinflammation. In this review, we discuss endogenous regulatory mechanisms that prevent thrombosis in the microcirculation, experimental approaches to induce microvascular thrombi, and clinical conditions associated with microvascular thrombosis. A greater understanding of the links between inflammation and thrombosis in the microcirculation is anticipated to provide optimal therapeutic targets for patients with diseases accompanied by microvascular thrombosis.

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.

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.

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.

Postinfectious Hemolytic Uremic Syndrome

Post-infectious hemolytic uremic syndrome (HUS) is caused by specific pathogens in patients with no identifiable HUS-associated genetic mutation or autoantibody. The majority of episodes is due to infections by Shiga toxin (Stx) producing Escherichia coli (STEC). This chapter reviews the epidemiology and pathogenesis of STEC-HUS, including bacterial-derived factors and host responses. STEC disease is characterized by hematological (microangiopathic hemolytic anemia), renal (acute kidney injury) and extrarenal organ involvement. Clinicians should always strive for an etiological diagnosis through the microbiological or molecular identification of Stx-producing bacteria and Stx or, if negative, serological assays. Treatment of STEC-HUS is supportive; more investigations are needed to evaluate the efficacy of putative preventive and therapeutic measures, such as non-phage-inducing antibiotics, volume expansion and anti-complement agents. The outcome of STEC-HUS is generally favorable, but chronic kidney disease, permanent extrarenal, mainly cerebral complication and death (in less than 5 %) occur and long-term follow-up is recommended. The remainder of this chapter highlights rarer forms of (post-infectious) HUS due to S. dysenteriae, S. pneumoniae, influenza A and HIV and discusses potential interactions between these pathogens and the complement system.

Vaccination uptake by vaccine-hesitant parents attending a specialist immunization clinic in Australia

Vaccine hesitancy (VH) is an issue of global concern. The quality of communication between healthcare providers and parents can influence parental immunization acceptance. We aimed to describe immunization uptake following specialist immunization clinic (SIC) consultation for Australian children of VH parents as a cohort, and according to pre-clinic parental position on immunization. At a single tertiary pediatric SIC (RCH, Melbourne) a retrospective descriptive study classified VH families according to 3 proposed parental positions on immunization at initial clinic attendance. Immunization status at follow up was ascertained via the Australian Children's Immunization Register and National HPV Program Register and compared between groups. Of the VH cohort, 13/38 (34%) families were classified as hesitant, 21 (55%) as late/selective vaccinators and 4 (11%) as vaccine refusers. Mean follow up post-SIC attendance was 14.5 months. For the overall VH cohort, the majority chose selective immunization (42%) following SIC consultation. When analyzed by pre-clinic parental position on immunization, there was a trend for hesitant families to proceed with full immunization, selective families to continue selective immunization and refusing families to remain unimmunised (p < 0.0001). The most commonly omitted vaccines were hepatitis B (66%) and Haemophilus influenzae type B (55%), followed by the meningococcal C conjugate vaccine (53%) and measles, mumps and rubella vaccine (53%). Immunization outcome appears to correlate with pre-clinic parental position on immunization for the majority of families attending a SIC in Australia, with selective immunization the most common outcome. Tailored communication approaches based on parental position on immunization may optimise clinic resources and engagement of families, but require prospective research evaluation.

Update on Streptococcus pneumoniae associated hemolytic uremic syndrome

PURPOSE OF REVIEW

Streptococcus pneumoniae associated hemolytic uremic syndrome (SpHUS) is defined by the occurrence of acute hemolytic anemia, thrombocytopenia and acute kidney injury in a patient with a S. pneumoniae infection. We review the pathophysiology, clinical course, treatment and prognosis for SpHUS. We also describe an expanded classification system that uses additional diagnostic criteria to identify more patients with a high likelihood of having SpHUS.

RECENT FINDINGS

SpHUS often may be underdiagnosed because of overlapping features with disseminated intravascular coagulation (DIC) and the lack of strict diagnostic criteria. The epidemiology has changed with the emergence of different pneumococcal serotypes as newer pneumococcal vaccines have been introduced.

SUMMARY

SpHUS accounts for 5-15% of all HUS cases. The majority of SpHUS patients have pneumonia and a low mortality rate in contrast to those with meningitis, who have a more severe clinical course. Although the pathogenesis of SpHUS remains unknown, the Thomsen-Friedenreich antigen seems to play a central role. S. pneumoniae produces neuraminidase, thereby exposing the Thomsen-Friedenreich antigen on the surface of cell membranes. Thomsen-Friedenreich antigen exposure can result in hemolysis and direct endothelial injury leading to HUS phenotype. Early identification of these patients is critical so that fresh frozen plasma may be avoided.

Management of hemolytic uremic syndrome

2011 has been a special year for hemolytic uremic syndrome (HUS): on the one hand, the dramatic epidemic of Shiga toxin producing E. coli -associated HUS in Germany brought the disease to the attention of the general population, on the other hand it has been the year when eculizumab, the first complement blocker available for clinical practice, was demonstrated as the potential new standard of care for atypical HUS. Here we review the therapeutic options presently available for the various forms of hemolytic uremic syndrome and show how recent knowledge has changed the therapeutic approach and prognosis of atypical HUS.

Pneumococcal disease manifestation in children before and after vaccination: what's new?

Pneumococcal infections remain a relevant cause of morbidity and mortality in children, especially in countries where vaccination has not been introduced. In contrast to the common belief by many pediatricians, the most important pneumococcal infections are of the respiratory tract and not invasive diseases. The recent pandemic of the H1N1 virus prompted studies to better understand the interaction between the influenza virus, Streptococcus pneumoniae, and pneumonia outcomes. Radiological findings of bacteremic pneumonia have been well investigated and besides the typical alveolar consolidation, a broad spectrum of atypical patterns has been reported. Molecular techniques, such as real-time polymerase chain reaction (PCR), can improve the detection of S. pneumoniae in sterile fluids, mainly in regions where previous antibiotic therapy is a common practice. In the post vaccination era, new manifestations of pneumococcal invasive disease, such as hemolytic uremic syndrome, have increased in association with parapneumonic empyema. Moreover, serotypes not included in PCV7, particularly serotypes 1, 3, 5, 7F, and 19A, have been among the most common isolates in pneumococcal disease. In Latin America, pneumococcal primary peritonitis has been described as an important clinical syndrome in a growing proportion of patients, mainly in girls. The development of newer and more specific diagnostic markers to distinguish bacterial and viral pneumonia are urgently sought, and will be especially pertinent after the introduction of pneumococcal conjugate vaccines with expanded serotypes. Such markers would minimize inappropriate diagnosis of false positive cases and treatment with antibacterial agents, while increasing positive predictive values for diagnosis of bacterial pneumonia. The extension of serotype coverage with the new conjugate vaccines is promising for pneumococcal infections and coverage against antibiotic-resistant strains.

Epidemiology of Streptococcus pneumoniae-induced hemolytic uremic syndrome in Utah children

BACKGROUND

Hemolytic uremic syndrome (HUS) is an uncommon complication of invasive pneumococcal disease (IPD) in children. Few studies examine the Streptococcus pneumoniae serotypes associated with HUS. Our objective was to describe the epidemiology of S. pneumoniae-related HUS (SP-HUS) and the serotypes associated with HUS in Utah children.

METHODS

We reviewed separate longitudinal databases of HUS and IPD. These included all children <18 years cared for at Primary Children's Medical Center, Salt Lake City, UT, with IPD from 1997 to 2008 and all children in Utah with HUS since 1971.

RESULTS

We identified 435 Utah children with culture-confirmed IPD (1997-2008) and 460 with HUS (1971-2008). There were no reported cases of SP-HUS before 1997. With the introduction of pneumococcal conjugate vaccine (PCV-7) in 2000, the percentage of IPD complicated by SP-HUS has increased from 0.3% to 5.6% (P < 0.001). Pneumonia (P = 0.051) and empyema (P = 0.012) were associated with the development of SP-HUS compared with IPD without SP-HUS. Children with SP-HUS also required ICU care and had longer stays than those with IPD alone. Only serotype 3 appeared associated with SP-HUS (P = 0.067).

CONCLUSIONS

We identified an increasing incidence of SP-HUS in Utah children. SP-HUS is a serious complication of IPD associated most frequently with pneumonia and empyema because of serotypes not included in the PCV-7, particularly serotype 3.