Shiga Toxin-Producing and Hemolytic Uremic Syndrome: A Study of the 2022 Outbreak in Turkey

Introduction

ETIOLOGY:

In diseases that cause thrombotic microangiopathy, endothelial damage occurs at the microvascular level, increasing the tendency to thrombosis. When diagnosing hemolytic uremic syndrome (HUS), it is important to evaluate other diseases that can cause microangiopathy [1]. HUS is made up of non-immune hemolytic anemia, fragmented red blood cells, low platelets, and acute kidney injury. Shiga toxin-associated HUS is the most common cause of acute kidney injury, accounting for approximately 90% of all HUS cases [2].

Escherichia coli 0157: H7 occurs after consuming undercooked meat or inadequately pasteurized dairy products or after contact with contaminated fomites loaded with Shiga toxin-producing enterohemorrhagic E. coli [3]. Shiga toxin-producing strains of E. coli (STEC) produce virulent-type toxins, such as Stx-1 and Stx-2. Stx-2 is more toxic, and both toxins are associated with complicated STEC infections; however, the incidence of HUS is higher in the Stx-2 strain [4,5]. In most countries, STEC serotype O157: H7 infection is the most common cause of HUS [6]. Other serotypes, however, have been identified in the disease’s etiology [7].

EPIDEMIOLOGY:

Each year, STEC causes 43 acute diseases and 3890 HUS cases per 100 000 people [8]. Studies in the literature on STEC-HUS primarily focus on pediatric cases, with an estimated incidence of 0.57 cases per 100 000 children. The incidence of HUS among adults increases as a result of environmental exposure in practices such as cattle breeding and agriculture. Atypical HUS (aHUS), in contrast to HUS, occurs significantly less frequently. However, aHUS exhibits significantly higher morbidity and mortality rates [9].

PATHOPHYSIOLOGY:

When STEC is taken into the digestive system from an external source, it penetrates the mucosal layer of the intestine and secretes Shiga toxin, which binds to the Gb3 receptor. Shiga toxin/Gb3 complex binds to cell ribosomes, inhibits protein synthesis, and causes inflammatory cytokine release and apoptosis. In addition to cytotoxic effects, Shiga toxin can activate the complement system by inhibiting complement factor H. Once in the bloodstream, Shiga toxin continues to bind to cells via the Gb3 receptor, which is most abundant in the glomerular vascular space. Shiga toxin causes endothelial damage through (1) direct cytotoxicity, (2) disruption of the hemostatic pathway, (3) increased cytokine release, and (4) activation of the alternative pathway. This endothelial damage causes thrombotic microangiopathy [9]. aHUS are usually associated with a genetic abnormality that affects regulation of the alternative complement system in conjunction with a provocative stress, such as infection.

EVALUATION:

Symptoms, travel status, laboratory data, and dietary history all contribute to the diagnosis of HUS. First, a comprehensive biochemistry panel and complete blood count tests should be performed. The appearance of schistocytes in the peripheral smear accompanied by high lactate dehydrogenase (LDH), indirect bilirubin, and hemoglobin, as well as low haptoglobin levels, is valuable in the diagnosis of hemolytic anemia [10].

Elevated amylase and lipase can be observed in approximately 20% of patients, due to pancreatic damage. In cases in which diarrhea is present, rapid stool sampling should be performed. A negative result for Shiga toxin does not rule out the disease. Although a low complement level is not specific, it is more suggestive of aHUS. Electrolyte disturbances and signs of acute kidney injury can be observed in patients. ADAMTS13 level should be studied to rule out thrombotic thrombocytopenic purpura. Prolonged prothrombin time, activated partial thromboplastin time, and elevated D-dimer levels are suggestive of disseminated intravascular coagulation [11].

Tests for the diagnosis of HUS are very valuable; however, in cases in which clinical suspicion is high, treatment should begin immediately.

TREATMENT:

In the treatment of typical HUS caused by STEC, supportive treatments, such as electrolyte replacement and fluid resuscitation, are performed. The risk of thrombosis should be kept in mind when using blood products. Patients with typical HUS caused by STEC should refrain from using antibiotics. In the treatment of atypical HUS, treatment should be started early, and eculizumab, which forms the basis of treatment, should be given early in patients with an indication [11].

In this study, we examined a large HUS outbreak caused by E. coli with serotype O104: H4 that occurred in the Western Black Sea Region of Turkey in July 2022. This major outbreak was primarily caused by a rare strain resembling enteroaggregative E. Coli with serotype O104: H4. An important difference of this strain was its ability to secrete Shiga toxin, which is characteristic for enterohemorrhagic E. coli (EHEC) strains.

Material and Methods

STATISTICAL ANALYSIS:

Statistical analysis was made by the Statistical Package for Social Sciences (SPSS) version 25 (IBM Corp, Armonk, NY, USA). Normality of variables was analyzed by the Kolmogorov-Smirnov test. Continuous variables are expressed either as mean±standard deviation or as median and minimum–maximum values, according to normality. The relationship between length of hospital stay and laboratory parameters was examined with the Spearman correlation test. In addition, the relationship between laboratory parameters at the time of admission and patients requiring eculizumab and plasmapheresis was examined with the Mann-Whitney U test. P values <0.05 were considered statistically significant.

Results

DEMOGRAPHIC RESULTS:

In this study, we presented the follow-up data of 21 adult patients who were admitted to our İntensive Care Unit (ICU) with HUS diagnosis in July 2022. The outbreak lasted for 2.5 months. Adult patients with HUS requiring treatment in the İntensive Care Unit were followed up in a single center. The average length of stay was 17 (2–56) days. The ages of the patients ranged between 22 and 81 years, and 4 were men and 17 were women. All patients lived in the Western Black Sea Region, where the outbreak occurred. All patients had a history of eating fruits and vegetables exposed to contaminated water. Eight patients (38.10%) had a history of antibacterial use (ciprofloxacin and meropenem) before admission to the ICU. Hemorrhagic diarrhea was present in 10 patients (47.6%). Oliguria was present in 16 patients (76.1%) at the time of admission.

CLINICAL RESULTS:

Cardiogenic involvement was seen in 1 patient (4.76%), neurogenic involvement in 5 patients (23.81%), pulmonary involvement in 19 patients (90.48%), and abdominal involvement in 21 patients (100%). Hemodialysis was performed in 10 patients (47.62%), and plasmapheresis was performed in 7 patients (33.33%). Acute kidney injury was present in 19 patients (90.4%) at the time of admission. Acute kidney injury developed in 20 patients (95.2%) during follow-up. Four patients (19.05%) received eculizumab treatment. All patients were defined as confirmed HUS cases.

Cardiac involvement developed in 1 patient, and the patient’s ejection fraction level decreased from 60% to 20% within 1 week, and pericardial effusion was detected. The patient’s cardiac magnetic resonance imaging revealed right atrial and right ventricular myocardial dysfunction. In the echocardiography performed before discharge, it was observed that the ejection fraction level of the patient increased up to 55%, and the pericardial effusion decreased, but the global mild hypokinetic state continued. After 3 months of follow-up, the patient’s ejection fraction level returned to normal. Pulmonary edema was detected in 19 patients. Non-massive hemoptysis developed in 2 of these patients. Five patients showed signs of neurological involvement. All of these patients had visual impairment, 3 had seizures, and 2 had impaired consciousness and extremity paresis. In patients with visual impairment, there were symptoms of decreased visual field and blurred vision. One patient developed transient blindness. In addition, visual impairment was the first observed neurological symptom. Before discharge, patients’ visual impairments improved.

Abdominal involvement (abdominal pain, vomiting, bleeding) was observed in all patients hospitalized in the ICU. Lower gastrointestinal system bleeding occurred in 2 patients and required erythrocyte suspension replacement. Evaluation of laboratory parameters, demographic characteristics, treatments, and extrarenal findings at the time of admission are shown in Tables 1 and 2.

Twenty-one patients, followed up for 3 months after ICU discharge, did not experience any permanent sequelae. Eight patients (38.10%) had a history of antibiotic use (ciprofloxacin and meropenem) before admission to the ICU. There was no significant difference in laboratory values performed during hospitalization between the patients who received and did not receive antibiotics prior to ICU admission. However, the highest NT-proBNP value was found to be significantly higher in those receiving antibiotics (P=0.02).The relationship between antibiotic use and laboratory parameters in patients with a history of antibiotic usage is shown in Table 3.

An inverse correlation was found between the total length of stay in the hospital and the GFR value at admission. A positive correlation was found between the length of hospital stay and LDH at admission, highest troponin I, and highest NT-proBNP values during follow-up. The relationship between total length of hospital stay and laboratory parameters is shown in Table 4.

Four patients who developed serious neurological complications received eculizumab treatment. Two of the patients received eculizumab treatment as a double dose, and 2 patients as a single dose. Two patients received eculizumab treatment on the second day of their ICU hospitalization, while the other 2 patients received it on the sixth day. It was observed that the creatinine, LDH, and NT-pro BNP values at the time of admission were significantly higher in patients receiving eculizumab. The relationship between laboratory test results of the patients during hospitalization and the patients who required eculizumab is shown in Table 5.

In patients treated with 2 doses of eculizumab (patient 7 and patient 14), there were 72 h between doses. Although low hemoglobin and thrombocyte levels persisted in the first 24 h of treatment in those receiving eculizumab, the patients’ neurological findings improved. Patients whose neurological symptoms improved did not receive the second dose of eculizumab after the first dose. We administered a second dose of eculizumab to 2 patients (patients 7 and 14) whose neurological symptoms did not improve. In 1 patient (patient 14), neurologic symptoms did not improve despite eculizumab treatment. Hemoglobin, platelet, creatinine, and LDH values before and after eculizumab treatment are shown in Table 6.

Plasmapheresis was performed on 7 patients (33.33%) who exhibited clinical deterioration and a change in consciousness. Since there was no clinical improvement in 4 of 7 patients, eculizumab was subsequently added to the treatment. It was observed that the creatinine, LDH, and amylase values were significantly higher in patients receiving plasmapheresis at the time of admission. The relationship between laboratory tests during hospitalization for patients receiving plasmapheresis is shown in Table 7.

Discussion

STUDY LIMITATIONS:

The limitations of our study are that the number of participants is relatively limited and does not represent a large population. In addition, stool culture could not be performed in all patients before admission to the ICU. Detailed microbiological characterization of the strains was therefore missing in some patients. One of our limitations was a lack of a specific indication for eculizumab treatment. The simultaneous application of plasmapheresis and eculizumab in some patients made it difficult to make a clear comparison in terms of prognosis. For future studies, we recommend conducting prospective studies with a larger population.

Conclusions

We want to point out that E, coli infections in adults are more likely to progress to HUS in epidemics, and that these infections are an important public health problem. We want to emphasize the importance of starting the treatment at an early stage and managing it at a single center, with a multidisciplinary approach. However, more comprehensive studies are needed. STEC is a significant health problem that causes serious illnesses. In this study, a statistically significant difference was detected between LDH, GFR, troponin, NT-proBNP parameters, and the length of hospital stay. Creatine and LDH values of patients requiring eculizumab and plasmapheresis at the time of admission were found to be statistically high. It should be kept in mind that eculizumab and plasmapheresis treatment can be required for patients with elevated creatine and LDH levels at the time of admission. Additionally, directing patients to centers where these treatments can be given can be important for early treatment.