Escherichia coli O121:H19 infection identified on microagglutination assay and PCR

Non‐O157 Shiga toxin‐producing Escherichia coli (STEC) strains are increasingly recognized as foodborne pathogens that trigger hemolytic uremic syndrome (HUS). The detection and isolation of these strains is important, but distinguishing their bacteriological profiles is difficult. A 2‐year‐old girl developed HUS with mild renal involvement 22 days after consuming barbecued meat. Clinical and laboratory findings gradually improved without specific treatment. Because neither enterohemorrhagic E. coli (EHEC) nor Shiga toxins were detected in stool cultures in a clinical laboratory and the patient tested negative for circulating antibodies to O157 lipopolysaccharide, the case was initially diagnosed as probable atypical HUS. Subsequent serodiagnostic microagglutination assay and polymerase chain reaction‐based molecular testing, however, indicated the presence of the EHEC O121:H19 strain with stx2. Thus, to correctly diagnose and treat HUS, a system for detecting non‐O157 STEC in a clinical setting is urgently needed.     

A time for reappraisal of “atypical” hemolytic uremic syndrome: should all patients be treated the same?

Atypical hemolytic uremic syndrome (HUS) refers to the triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury in the absence of Shiga toxin-producing Escherichia coli exposure or Streptococcus pneumoniae infection. Currently, approximately 50?% of the atypical cases have demonstrable mutations in complement regulatory proteins. Historically, the diagnosis of atypical HUS portends a poor prognosis with a high rate of disease recurrence, progression to end-stage renal disease, and death. However, it is now evident that atypical HUS actually encompasses a heterogeneous group of disorders, and there are reports suggesting that some cases of atypical HUS have a favorable prognosis, similar to that of diarrhea-associated disease. We present three patients with the atypical HUS phenotype who had complete renal recovery and no disease recurrence. We believe it is important to distinguish those cases of atypical HUS associated with disorders of complement regulatory proteins from other idiopathic causes of nondiarrheal HUS given the implications for prognosis and treatment. Conclusion: Given the heterogeneous nature and variable prognosis of atypical HUS, treatment should be carefully considered prior to the use of long-term plasma therapy and/or eculizumab.     

Follow‐up of children with infection‐associated haemolytic uraemic syndrome 1979–1995: Would eculizumab have improved prognosis?

The late outcome in 55 children with infection‐mediated haemolytic uremic syndrome (Shiga Toxin E Coli (STEC)‐HUS and pneumococcal HUS) observed in 1979–1995 was followed up 23 years after disease onset. Of these, two were later confirmed to have atypical HUS (aHUS). Furthermore, of this population, five children had impaired kidney function at 3‐months follow‐up, which continued to deteriorate. These children had significant oliguria/anuria and hypertension during their illness requiring early dialysis and antihypertensive therapy. At 23 years post‐disease onset, all five (100%) of these children have developed end‐stage kidney disease or chronic kidney disease. Eculizumab is a monoclonal antibody that binds with high affinity to the C5 protein of the complement pathway, a major component of the pathophysiology of infection‐mediated HUS. There are no long‐term randomised controlled trials in the literature to support its use in such cases. Our 23‐year follow‐up of a population of severely affected children with infection‐mediated HUS demonstrates a high percentage of chronic kidney disease and end‐stage kidney disease (19%). Randomised controlled trials with eculizumab are now being conducted in this affected cohort.     

Pathogenic functions and diagnostic utility of cytokines/chemokines in EHEC‐HUS

Hemolytic ? uremic syndrome (HUS) is a severe complication of infection by Shiga toxin (STx)‐producing enterohemorrhagic Escherichia coli. Hemolytic ? uremic syndrome is defined clinically as a triad of non‐immune microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injuries. Neurologic complications such as acute encephalopathy are also observed. In humans, endothelial cells, proximal tubular epithelial cells, mesangial cells, podocytes, intestinal epithelial cells, and monocytes / macrophages are susceptible to STx‐mediated injury. Shiga toxin induces the secretion of inflammatory cytokines and chemokines from susceptible cells, including tumor necrosis factor‐α interleukin (IL)‐1, IL‐6, and IL‐8. These cytokines and chemokines contribute to the pathogenesis of HUS and encephalopathy by enhancing STx‐induced cytotoxicity and inducing inflammatory cell infiltration. Serum cytokine/chemokine levels are therefore useful as indicators of disease activity and predictors of progression from acute kidney injury to chronic kidney disease. Anti‐inflammation therapy combined with apheresis to remove excessive cytokines / chemokines and methylprednisolone pulse therapy to suppress cytokine/chemokine production may be an effective treatment regimen for severe E. coli‐associated HUS. However, this regimen requires careful monitoring of potential side effects, such as infections, thrombus formation, and hypertension.     

Mikroangiopatie zakrzepowe: nowe spojrzenie na patofizjologię i terapię

Thrombotic microangiopathy (TMA) is defined as process of endothelial cell damage, affecting mainly arterioles and capillaries, resulting in intraluminal thrombosis, platelet clumping, microangiopathic hemolytic anemia and occlusion of the vessel lumen. TMA encompasses hemolytic uremic syndromes (HUS) and thrombotic thrombocytopenic purpura (TTP), differentiated mainly by microbiologic tests and activity of protein ADAMTS13. Currently, four types of hemolytic uremic syndrome are distinguished: typical, atypical, secondary and idiopathic. Typical HUS is caused by bacterial toxins, mainly Shiga toxin-producing Escherichia coli (STEC-HUS). Atypical HUS develops as a result of pathologic activation of alternative complement pathway, mainly as a genetic defect. Secondary HUS includes various diseases with underlying pathophysiology causing development of microangiopathy. Idiopathic HUS is diagnosed after exclusion of other thrombotic microangiopathies and genetic defects. Thrombotic thrombocytopenic purpura results after decrease of activity of metalloproteinase ADAMTS13, which physiologically cleaves multimers of von Willebrand factor to subunits with lower procoagulation activity. ADAMTS13 deficiency can be congenital or acquired. Inherited forms are based on recessive mutations of ADAMTS13 gene. Acquired TTP are of immunological character, and appears with autoantibodies against ADAMTS13 protein. The predisposing factor for these antibodies is presence of HLA-DRB1*11 antigen. This review presents current knowledge on definitions, pathophysiology, differential diagnostics and therapy of thrombotic microangiopathies. A new perspective on targeted therapy in hemolytic uremic syndrome, based on the use of eculizumab, monoclonal antibody against C5 protein of complement pathway, is underlined.     

Post‐transplant recurrence of atypical hemolytic uremic syndrome in a patient with thrombomodulin mutation

HUS is characterized by hemolytic anemia, thrombocytopenia, and acute renal failure. While “typical” HUS is usually associated with Shiga toxin‐producing Escherichia coli infections and recovers in the majority of cases, aHUS is caused by mutations of complement components or antibodies against CFH leading to uncontrolled activation of alternative complement pathway and often to ESRD. Recently, THBD gene mutations have been reported in aHUS. Theoretically, the risk of disease recurrence after renal transplantation should be low because THBD is primarily a membrane‐bound protein expressed by endothelial cells; however, a small proportion of THBD is present as a soluble form in plasma. We report the case of a 19‐yr‐old man with aHUS secondary to a THBD mutation that relapsed twice after two renal transplantations performed 12 yr apart. Despite successful control of HUS with plasma exchange and eculizumab after the second transplantation, the graft was ultimately lost due to severe steroid‐resistant cellular rejection. The present report suggests that THBD mutations may favor‐relapse of aHUS after renal transplantation.     

Autoimmune‐type atypical hemolytic uremic syndrome treated with eculizumab as first‐line therapy

We report a case of atypical hemolytic uremic syndrome (aHUS) in a 4‐year‐old boy. Although the patient had the typical triad of aHUS (microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury), urgent dialysis was not indicated because he had neither oliguria nor severe electrolyte abnormality. He was given eculizumab as first‐line therapy, which led to significant clinical improvement, thus avoiding any risk of complications associated with plasma exchange and central venous catheterization. Retrograde functional analysis of the patient's plasma using sheep erythrocytes indicated an increase in hemolysis, suggesting impairment of host cell protection by complement factor H. The use of eculizumab as first‐line therapy in place of plasma exchange might be reasonable for pediatric patients with aHUS.     

Frequency of Shiga Toxin-Producing Genes of Escherichia Coli Isolated from Diarrheic Stools of Iranian Children by PCR

Objective

Shiga toxin-producing E. coli (STEC) is a pathogenic E. coli that may cause hemolytic uremic syndrome (HUS) after diarrheal disease through Shiga toxins. Management of the patients with STEC infection is different from that of other diarrheal diseases due to increase in frequency of HUS after antibiotic administration. Few studies were conducted in Iran and epidemiology of STEC remains obscure; this necessitates examination of stools especially in young children for this bacterium.

Methods

We determined the frequency of STEC in 947 E. coli strains isolated from diarrheal stools of children less than 14 years in Tehran with conventional culture methods and multiplex-PCR via determining the STX1 and STX2 genes, between October 2008 and September 2009. We also evaluated the association between stool exam findings and presence of STEC.

Findings

Twenty seven (2.8%) of E. coli isolates were positive for STX1 or STX2 genes, most of which occurred in spring (P<0.05). There was no significant association between STEC positivity and stool exam findings. Eighteen out of 27 (66.7%) Shiga toxin positive samples were isolated from males and the rest from females. The most common STX-positive diarrheal samples showed loose consistency (P<0.017).

Conclusion

Although the low frequency of STEC in our population indicates that it is not a major problem in our population, STEC should be regarded as an important infection because of its severe consequences. Further studies with greater sample size are needed to confirm our results.     

Decreased sialylation of IgA1 O‐glycans associated with pneumococcal hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) in children is usually caused by Shiga‐like toxin‐producing Escherichia coli, but approximately 5% of cases are caused by invasive pneumococcal infection (P‐HUS). Reported herein is the case of a 9‐month‐old HUS patient with pneumococcal meningitis who needed hemodialysis for 12 days. Decreased sialylation was characterized in both transferrin N‐glycans and IgA1 O‐glycans, analyzed in the acute phase on mass spectrometry, consistent with S. pneumonia‐produced sialidases hydrolyzing both α2,3‐ and α2,6‐linked sialic acids. The method will complement the T‐antigen activation test and help to understand the molecular pathology related to P‐HUS.     

Surveillance of hemolytic uremic syndrome in children less than 15 years of age, a system to monitor O157 and non-O157 Shiga toxin-producing Escherichia coli infections in France, 1996-2006

BACKGROUND: Since the 1980s, Shiga toxin-producing Escherichia coli (STEC), especially E. coli O157:H7, has been an important cause of food borne disease in industrial countries. In France, as there was no routine screening for STEC in clinical laboratories, enhanced surveillance of hemolytic uremic syndrome (HUS) in children less than 15 years of age was established in 1996 to monitor trends in the incidence of STEC infections. METHODS: The surveillance system was based on a voluntary national network of pediatricians of 31 pediatric nephrology units in public hospitals. RESULTS: From 1996 to 2006, the mean annual incidence of HUS was 0.71 cases per 100,000 children less than 15 years of age and 1.87 cases per 100,000 children less than 5 years of age. STEC infections were confirmed in 66% of patients; STEC O157 was the most common serogroup identified in STEC-related HUS (83%). In this 11-year period, 96% of HUS cases were sporadic and only 2 outbreaks caused by STEC O157 and by a dual infection of STEC O26 and O80 were detected. CONCLUSIONS: An evaluation of the surveillance of pediatric HUS showed that it is a simple and useful system for monitoring trends in STEC infections in France. It provides the information needed to measure the impact of new and changing vehicles of STEC transmission, and evaluate the effectiveness of prevention measures.     

Fulminant recurrence of atypical hemolytic uremic syndrome during a calcineurin inhibitor-free immunosuppression regimen

Recurrence of hemolytic uremic syndrome (HUS) after kidney transplantation is frequent, occurring almost exclusively in patients with atypical HUS, which is not caused by Escherichia coli gastroenteritis and in which diarrhea is absent. Calcineurin inhibitors are associated with recurrence of HUS. In two children who underwent living donor kidney transplantation for atypical HUS, we pre-emptively employed sirolimus in a calcineurin inhibitor-free immunosuppression regimen. Both children had excellent early graft function, yet both developed severe recurrent disease and subsequently lost their grafts. Avoidance of calcineurin inhibitors did not prevent recurrence of severe HUS and graft loss. Transplantation for severe atypical HUS remains problematic.     

Syndrome hémolytique et urémique post-diarrhéique : Quand y penser ? Quel suivi ?

Haemolytic uremic syndrome (HUS) is characterized by thrombotic microangiopathy with acute renal failure, haemolytic anaemia with schizocytes and thrombocytopenia. Typical forms (D⁺ HUS) are caused by gastrointestinal infection with Escherichia coli species producing verotoxines (or Shiga toxins, STEC). It is estimated that 5-8 % of infected individuals will develop HUS following STEC infection. E. coli O157:H7 is the most commonly involved serotype and can lead to D⁺ HUS in 15 % of young infected children. Vehicles of STEC transmission are contaminated food (ground beef, unpasteurised dairy products, unwashed and uncooked fruit and vegetables), person-to-person transmission and contact with farm animals with STEC. After an average incubation period of 3 to 8 days, patients develop painful bloody diarrhoea followed by systemic toxinemia. This may lead to thrombotic microangiopathy with endothelial damage and activation of local thrombosis. Since 1996, the Institut de Veille Sanitaire (InVS) centralises all notified French cases of D⁺ HUS in children less than 15 years of age and investigates cases regrouped by time and place for the presence of STEC risk factors. The average annual incidence ranges between 0.6 and one for 100 000 children younger than 15 years and with a peak at 1 year of age. Fifty-one percent of HUS occur between June and September. Patients with a suspicion of STEC infection or bloody diarrhoea should not receive antibiotics, antimotility agents, narcotics and non-steroidal anti-inflammatory drugs. Maintenance optimal hydration provides nephroprotection. The management of HUS remains supportive. Dialysis was required for 46 % of HUS cases in 2009. For similar indication, peritoneal dialysis has to be a first choice treatment. Neurological injury is the most frequent non-renal complication and the first cause of death. Early initiation of plasmapheresis might improve the prognosis. Overall mortality rate ranges between 1 and 5 %. One third of patients suffer from long-term renal morbidity such as proteinuria, arterial hypertension and decrease of glomerular filtration rate. The longer the duration of anuria, the greater the risk of sequellae. Any patient with a history of HUS needs a long-term renal follow-up.     

Cluster of hemolytic-uremic syndrome caused by Shiga toxin-producing Escherichia coli O26:H11

BACKGROUND: The epidemiology and clinical characteristics of the hemolytic-uremic syndrome (HUS) caused by Escherichia coli O157:H7 are well-known, but HUS attributable to non-O157:H7 Shiga toxin (Stx)-producing E. coli (STEC) are less thoroughly described. Here we report a cluster of HUS cases caused by STEC O26:H11 the most common non-O157:H7 STEC isolated from sporadic cases of HUS in Europe. METHODS: Three children between 13 and 17 months of age, living in the same small town, developed HUS within an interval of 5 days. We present clinical and microbiologic data on the patients and their infecting isolates. RESULTS: The clinical course ranged from mild uncomplicated HUS to severe HUS complicated by multiorgan involvement. Microbiologic investigation demonstrated STEC of serotype O26:H11 in stools of all the patients. The phenotypic and molecular characterization of the STEC O26:H11 isolates demonstrated that these strains were identical and, unusual for STEC O26, they harbored the stx2 but not the stx1 gene. None of the patients had evidence of STEC O157:H7 infection either by culture or by E. coli O157 serology. The source of the STEC O26:H11 infection was undetermined. CONCLUSIONS: Our results demonstrate that diagnostic procedures based on the detection of stx genes and/or Stx production and subsequent subtyping of the isolates using molecular methods are necessary to identify such outbreaks caused by non-O157:H7 STEC.     

Saliva IgM and IgA are a sensitive indicator of the humoral immune response to Escherichia coli O157 lipopolysaccharide in children with enteropathic hemolytic uremic syndrome

Saliva antibodies to Escherichia coli O157 were investigated as markers of the immune response in children with enteropathic hemolytic uremic syndrome (HUS). Paired serum and saliva samples were collected from 22 children with HUS during acute disease and convalescence and were tested for E. coli O157 lipopolysaccharide (LPS)-specific IgM and IgA antibodies by ELISA. Serum and saliva samples from 44 age-matched controls were used to establish the cut-off values. Elevated levels of IgM and/or IgA antibodies to O157 LPS were detected in saliva of 13/13 HUS patients with Shiga toxin-producing E. coli (STEC) O157 in stool culture and from 4 of 5 HUS patients in whom STEC were not detected. These results closely mirrored the results obtained with paired serum samples. In contrast, saliva and serum samples from four children with STEC isolates belonging to O-groups O26, O145 (n = 2), and O165 lacked detectable O157 LPS-specific antibodies. The specificity of the ELISA was confirmed by western blotting. In STEC O157 culture-confirmed cases, the sensitivity of the ELISA was 92% for saliva IgM and IgA, based on the first available sample, and 100% and 92%, respectively, when subsequent samples were included. The specificity was 98% for IgM and 100% for IgA. Children with E. coli O157 HUS demonstrate a brisk, easily detectable immune response as reflected by the presence of specific antibodies in their saliva. Saliva-based immunoassays offer a reliable, noninvasive method for the diagnosis of E. coli O157 infection in patients with enteropathic HUS.     

Pathogenesis, treatment, and therapeutic trials in hemolytic uremic syndrome

Diarrhea-associated hemolytic uremic syndrome is one of the most common causes of acute renal failure in childhood. Nearly all cases are the result of an antecedent infection by Shiga toxin--producing strains of Escherichia coli, especially the O157:H7 serotype. Most cases occur after ingestion of contaminated meat; however, new food sources such as leaf lettuce, alfalfa sprouts, and goat's milk have been identified, and diarrhea-associated hemolytic uremic syndrome can occur after exposure to contaminated water in recreational swimming sites. Diarrhea-associated hemolytic uremic syndrome is a systemic disease with activation of a variety of inflammatory cytokines. Kidney injury may result from direct effects of the Shiga toxin on renal tubular epithelial cells as well as endothelial cells. Early diagnosis of diarrhea-associated hemolytic uremic syndrome may be expedited by the introduction of new techniques to rapidly detect toxin and microorganism in stool samples. Optimal therapy of diarrhea-associated hemolytic uremic syndrome includes intensive management of the renal failure and serious extrarenal complications that may occur during the course of disease. The role of antibiotics in prevention and amelioration of diarrhea-associated hemolytic uremic syndrome remains controversial. Experimental therapies that are undergoing evaluation in clinical trials include SYNSORB Pk (SYNSORB Biotech, Inc., Calgary, Alberta, Canada), a drug designed to bind Shiga toxin in the lumen of gastrointestinal tract. Immunization strategies are also being developed and tested. It is hoped that with continued progress in this field the incidence of diarrhea-associated hemolytic uremic syndrome in children will be substantially reduced in the coming years.     

Cardiac Failure in Hemolytic Uremic Syndrome and Rescue with Extracorporeal Life Support

Extrarenal involvement manifesting in the cardiovascular system is a rare but potentially fatal complication of hemolytic uremic syndrome (HUS). Current treatment is aimed at cardiovascular supportive measures while awaiting organ recovery. However, there are cases in which this recovery never occurs, and patients succumb secondary to heart failure. We report two cases of severe cardiac failure in children in the acute phase of HUS and the use of extracorporeal membrane oxygenation (ECMO) to support one patient to cardiac recovery. Clinicians should be aware of this potentially life-threatening cardiac involvement and should consider the use of ECMO for potentially salvageable children with HUS.     

Atypical hemolytic uremic syndrome responsive to steroids and intravenous immune globulin

Atypical hemolytic uremic syndrome remains a challenge to diagnose and treat, with significant acute morbidity and risk for progression to end stage renal disease. Treatment strategies center on plasma exchange but do not necessarily affect the progression of disease. We report the case of a patient with atypical HUS resulting from a mutation in the complement pathway who responded to treatment with steroids and IVIG, therefore avoiding transfusion or plasma exchange. Pediatr Blood Cancer 2009;53:90–91. © 2009 Wiley‐Liss, Inc.     

Nationwide study of haemolytic uraemic syndrome: clinical, microbiological, and epidemiological features.

AIMS: To establish the incidence and aetiology of haemolytic uraemic syndrome (HUS) in Australia and compare clinical and microbial characteristics of sporadic and outbreak cases. METHODS: National active surveillance through the Australian Paediatric Surveillance Unit with monthly case notification from paediatricians, July 1994 to June 1998. Children under 15 years presenting with microangiopathic haemolytic anaemia, thrombocytopenia, and acute renal impairment were identified. RESULTS: Ninety eight cases were identified (incidence 0.64 per 10(5) children <15 years/annum and 1.35 per 10(5) children <5 years/annum). Eighty four were associated with diarrhoea (64 sporadic, 20 constituting an outbreak) and 14 were atypical. Shiga toxin producing Escherichia coli (STEC) O111:H- was the most common isolate in sporadic HUS and caused the outbreak. However O111:H- isolates from outbreak and sporadic cases differed in phage type and subtyping by DNA electrophoresis. STEC isolates from sporadic cases included O26:H-, O113:H21, O130:H11, OR:H9, O157:H-, ONT:H7, and ONT:H-. STEC O157:H7 was not isolated from any case. Only O111:H- isolates produced both Shiga toxins 1 and 2 and possessed genes encoding E coli attaching and effacing gene (intimin) and enterohemolysin. Outbreak cases had worse gastrointestinal and renal disease at presentation and more extrarenal complications. CONCLUSIONS: Linking national surveillance with a specialised laboratory service allowed estimation of HUS incidence and provided information on its aetiology. In contrast to North America, Japan, and the British Isles, STEC O157:H7 is rare in Australia; however, non-O157:H7 STEC cause severe disease including outbreaks. Disease severity in outbreak cases may relate to yet unidentified virulence factors of the O111:H- strain isolated.     

Prognosis and pathological characteristics of five children with non-Shiga toxin-mediated hemolytic uremic syndrome

BACKGROUND: The three major signs of hemolytic uremic syndrome (HUS) are hemolytic anemia, thrombopenia and acute renal failure. HUS is classified into Shiga toxin-mediated HUS (Stx-HUS) and non-Shiga toxin-mediated HUS (nStx-HUS). The prognosis of nStx-HUS is reported to be less favorable than that of Stx-HUS. Although the association between the prognosis and pathological characteristics of HUS have been reported such that the prognosis was considered to be poor for thrombotic microangiopathy (TMA) with predominant arterial involvement (arterial TMA), good for TMA with predominant glomerular involvement (glomerular TMA) and dependent on the extent of necrosis in cases of renal cortical necrosis, it is not yet clear whether pathological findings are also related to the renal prognosis of nStx-HUS cases. Therefore the purpose of the present paper was to analyze renal biopsy findings and prognosis for five children with nStx-HUS. METHODS: Clinical records of five cases of nStx-HUS among 74 cases of diagnosed HUS were reviewed, and information and data were summarized. RESULTS: Histological examination of the kidney led to the diagnosis of arterial TMA in three cases, and glomerular TMA and severe renal cortical necrosis in one case each. Analysis of the relationship between renal histological findings and the prognosis found that three patients with arterial TMA and one patient with severe renal cortical necrosis later developed end-stage renal failure while one patient with glomerular TMA has continued to show normal renal function. CONCLUSIONS: These findings indicate that pathological findings are closely related to the prognosis in cases of nStx-HUS.     

Haemolytic uraemic syndrome and thrombotic thrombocytopenic purpura

This review will focus on the classification, symptoms, pathology, pathogenesis and management of haemolytic uraemic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP). HUS is characterized by microangiopathic haemolytic anaemia, thrombocytopenia and acute renal failure. Typical cases have been associated with infections caused by Shiga toxin (Stx)-producing bacteria manifested by a diarrhoeal prodrome. Atypical cases have heterogeneous aetiologies not associated with Stx. Certain cases may be hereditary and mutations in complement factor H have been identified in a subset of these patients. TTP is a similar condition characterized by microangiopathic haemolytic anaemia, thrombocytopenia, nephropathy, fever and neurological symptoms associated with mutations in the von Willebrand cleaving protease. The pathological lesion has been termed thrombotic microangiopathy revealing small vessel lesions and platelet thrombosis leading to obstruction of blood flow. Supportive management reduces morbidity and mortality. Patients with atypical HUS and TTP may benefit from specific treatment with plasma infusions or exchange.