Severe acute hepatitis and acute liver failure of unknown origin in children: a questionnaire-based study within 34 paediatric liver centres in 22 European countries and Israel, April 2022

Developing a syndromic surveillance tool to support the epidemiological investigation into paediatric acute hepatitis of unknown aetiology in England

BACKGROUND

During 2022, a new public health threat emerged when cases of paediatric acute hepatitis of unknown aetiology (HUA) were identified in children aged under 16 years old in the United Kingdom (UK). At the time, the epidemiology and extent of cases was based upon limited and non-standardised reporting from hospitals and liver units. We aimed to adapt existing real-time syndromic surveillance systems to support the epidemiological investigation of cases of HUA presenting to emergency departments (EDs) in England.

METHODS

Syndromic surveillance is generally based on the collection of patient symptoms or chief complaints, which are collected using automated routines in near real-time. Here, we used an existing ED syndromic surveillance system monitoring daily patient attendances across a network of approximately 150 EDs in England. Clinical diagnosis codes related to the potential symptoms associated with the HUA incident were selected and attendance data monitored retrospectively and prospectively during the incident.

RESULTS

From 2 April 2018 to 31 December 2021, there were small sporadic numbers of daily ED attendances for 'liver conditions' in children with no observed secular trends or seasonality across the 1 to 4 and 5 to 14 years age groups. The period 2 April to 29 July was compared across each year included in the analysis. Mean daily HUA attendances during 2018 to 2021 was 0.05 and 0.22 for 1 to 4 and 5 to 14 years respectively, however in 2022 there were 0.26 and 0.42 mean daily attendances. This represented an increase of 377% and 94% in the 1 to 4 and 5 to 14 years age groups, respectively. From June 2022, daily syndromic 'liver condition' attendances appeared to decrease and the rate of increase in cumulative attendances slowed.

CONCLUSIONS

We demonstrate how syndromic surveillance provided support to the HUA outbreak using an existing syndromic surveillance framework to develop new indicators based on the newly emerging clinical symptoms. The outputs from the syndromic tool matched clinical and epidemiological findings with respect to trends in other HUA-related data, including clinical and laboratory reports, over time. This work demonstrates the potential for syndromic surveillance supporting the epidemiological surveillance of hepatitis and providing a valuable tool for the real-time management of future unknown health threats.

Investigation of an outbreak of novel hepatitis of unknown aetiology in children and adolescents, Ireland, 2021 to 2023

An outbreak of severe acute hepatitis of unknown aetiology in children (HUAC) was reported by the United Kingdom (UK) in spring 2022. Within days, a corresponding increase was identified in Ireland. A multi-agency incident management team (IMT), led by the Health Protection Surveillance Centre (HPSC), established a national case definition, trawling questionnaire, testing protocol and communications plan. Between 1 October 2021 and 12 May 2023, 44 probable and three possible cases of HUAC were identified in Ireland with a median age of 3 years. Adeno-associated virus 2 (AAV2), detected in 18 of 31 probable cases, and SARS-CoV-2 antibodies in 22 of 37 of probable cases were the most common infectious agents, followed by human herpes virus 7 (18/33) and adenovirus (20/44). Immunological findings included the human leukocyte antigen (HLA) class II HLA-DRB1*04:01 allele in 17 of 32 cases. Autoantibodies were found in 15 of 40 patients. Our findings corroborate those of the UK, which suggested a link between HUAC and AAV2 and another virus, in children predisposed due to presence of a particular HLA class II type. Close collaboration with the UK, the European Centre for Disease Prevention and Control (ECDC) and World Health Organization (WHO) was invaluable in the investigation.

Using Laboratory Test Results for Surveillance During a New Outbreak of Acute Hepatitis in 3-Week- to 5-Year-Old Children in the United Kingdom, the Netherlands, Ireland, and Curaçao: Observational Cohort Study

Background

In March 2022, a concerning rise in cases of unexplained pediatric hepatitis was reported in multiple countries. Cases were defined as acute hepatitis with serum transaminases >500 U/L (aspartate transaminase [AST] or alanine transaminase [ALT]) in children aged 16 years or younger. We explored a simple federated data analytics method to search for evidence of unreported cases using routinely held data. We conducted a pragmatic survey to analyze changes in the proportion of hospitalized children with elevated AST or ALT over time. In addition, we studied the feasibility of using routinely collected clinical laboratory results to detect or follow-up the outbreak of an infectious disease.

Objective

We explored a simple federated data analytics method to search for evidence of unreported cases using routinely held data.

Methods

We provided hospitals with a simple computational tool to enable laboratories to share nondisclosive summary-level data. Summary statistics for AST and ALT measurements were collected from the last 10 years across all age groups. Measurements were considered elevated if ALT or AST was >200 U/L. The rate of elevated AST or ALT test for 3-week- to 5-year-olds was compared between a period of interest in which cases of hepatitis were reported (December 1, 2021, to August 31, 2022) and a prepandemic baseline period (January 1, 2012, to December 31, 2019). We calculated a z score, which measures the extent to which the rate for elevated ALT or AST was higher or lower in the period of interest compared to a baseline period, for the 3-week- to 5-year-olds.

Results

Our approach of sharing a simple software tool for local use enabled rapid, federated data analysis. A total of 34 hospitals in the United Kingdom, the Netherlands, Ireland, and Curaçao were asked to contribute summary data, and 30 (88%) submitted their data. For all locations combined, the rate of elevated AST or ALT measurements in the period of interest was not elevated (z score=-0.46; P=.64). Results from individual regions were discordant, with a higher rate of elevated AST or ALT values in the Netherlands (z score=4.48; P<.001), driven by results from a single center in Utrecht. We did not observe any clear indication of changes in primary care activity or test results in the same period.

Conclusions

Hospital laboratories collect large amounts of data on a daily basis that can potentially be of use for disease surveillance, but these are currently not optimally used. Federated analytics using nondisclosive, summary-level laboratory data sharing was successful, safe, and efficient. The approach holds potential as a tool for pandemic surveillance in future outbreaks. Our findings do not indicate the presence of a broader outbreak of mild hepatitis cases among young children, although there was an increase in elevated AST or ALT values locally in the Netherlands.

The clinical characteristics and SARS-CoV-2 infection in children of acute hepatitis with unknown aetiology: A meta-analysis and systematic review

The World Health Organization has issued a global alert on Acute Severe Hepatitis of Unknown Aetiology (AS-HEP-UA) since 23 April 2022,and there was still uncertainty regarding the association of AS-HEP-UA with SARS-CoV-2 as well as adenovirus. This study aimed to summarize the infection of SARS-CoV-2 and co-infections with adenovirus, as well as clinical features and outcomes in patients with AS-HEP-UA. PubMed, Embase, Web of Science, and the Cochrane Library were searched from 1 October 2021 to 8 December 2022 for studies about patients with AS-HEP-UA. This study was registered in the PROSPERO database (CRD42023385056). We has included 14 eligible articles. The main clinical features of AS-HEP-UA were jaundice (65%) and vomiting (59%), while other clinical features included diarrhea (45%), abdominal pain (37%), and fever (31%), roughly 10% of the children required liver transplantation. The overall positivity rate for SARS-CoV-2 was 21.6% (95% CI: 0.126-0.319), with 25.5% (95% CI: 0.161-0.358) for previous infections. The positivity rate for adenovirus infection was 58.6% (95% CI:0.429-0.736) while co-infection with SARS-CoV-2 was 17.5% (95% CI: 0.049-0.342). Moreover, we found that the positive rate of SARS-CoV-2 for this hepatitis outbreak was correlated with region by subgroup analysis. In conclusion, the positive rate of adenovirus was higher than SARS-CoV-2, and the relationship between AS-Hep-UA and COVID-19 is not significant. However, it cannot be excluded that the COVID-19 epidemic is an indirect causative agent of AS-Hep-UA, which requires a larger cohort of AS-Hep-UA patients to uncover additional findings.

Distinct Patterns of Liver Chemistry Changes in Pediatric Acute Hepatitis of Unknown Origin and COVID-19 Patients: A Systematic Review

In 2021 and 2022, there were noted to be clusters of pediatric acute hepatitis of unknown origin (AHUO) occurring across the globe. While there was not necessarily a global increase in cases, understanding the pattern of liver injury in AHUO is crucial to properly identify cases of this unexplained phenomenon, especially since it occurred simultaneously with a global resurgence of COVID-19. The objective of this study was to contrast the patterns in liver-relevant biochemical data from COVID-19 patients and AHUO. Studies reporting liver chemistries for cases of AHUO and COVID-19 were identified by a systematic review and search of the literature. For each case, alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin, direct bilirubin, and international normalized ratio (INR) levels were extracted as available. These were normalized to multiples of the upper limit of normal by patient age. There were statistically significant greater elevations of ALT and AST in patients with AHUO than in those with COVID-19. Only a subset of patients with COVID-19 had an AST or ALT greater than the normal range. INR elevation could be substantial for both conditions but was also statistically higher in the AHUO group. Liver chemistry changes were not statistically correlated with age. The pattern of liver chemistry changes between AHUO and COVID-19 have some distinctions, which suggests that AHUO is not a phenomenon driven primarily by SARS-CoV-2 infection alone. Differentiating AHUO and COVID-19 would be challenging based on patterns of liver chemistry changes alone.

Demystifying the global outbreak of severe acute hepatitis of unknown aetiology in children: A systematic review and meta-analysis

BACKGROUND

The sudden outbreak of severe acute hepatitis of unknown aetiology (SAHUA) in the first half of 2022 affected more than 1010 children in 35 countries worldwide. Dire clinical outcomes, such as acute liver failure necessitating transplantation, neurological symptoms, long-term sequelae, and death, highlight the need to determine the pathogenesis of this condition. Hypotheses on the aetiology include adenovirus and SARS-CoV-2 infections and an aberrant immune response to multiple pathogen exposure following lifting of lockdown measures but further investigation is required to reach an informed consensus.

METHODS

A literature search was performed on MEDLINE and EMBASE in accordance with PRISMA guidelines for systematic reviews. Primary studies reporting data on severe acute hepatitis of unknown aetiology in children from the COVID-19 era were selected for inclusion in our review. Data on patient demographics, clinical presentation and outcomes, and diagnostic testing for coinfection were extracted. Meta-analysis used a random-effects model.

RESULTS

The 33 included studies (30 case series and 3 case-control studies) described a total of 3636 cases of SAHUA (reported 1 January, 2019-31 December, 2022), with a median age of 3.5 years. Of these, 214 children (5.9%) received a liver transplant and 66 (1.8%) died. Whilst data on diagnostic testing was incomplete, the most frequently detected coinfections were with adenovirus and/or adeno-associated virus 2 (AAV2). Other common childhood respiratory and enteric pathogens, such as enterovirus, rhinovirus, and herpesviruses (EBV and HHV-6), were also identified.

CONCLUSION

Coinfection with AAV2 and other common childhood pathogens may predispose children to develop this novel severe hepatitis. Altered susceptibility and response to such pathogens may be a consequence of immunological naivety following pandemic restrictions. Further investigations are needed to generate high-quality evidence on aetiology for different patient demographics and geographical areas.

Paediatric acute hepatitis of unknown aetiology: a national surveillance investigation in the USA during 2021 and 2022

BACKGROUND

Adenovirus is a known cause of hepatitis in immunocompromised children, but not in immunocompetent children. In April, 2022, following multiple reports of hepatitis of unknown aetiology and adenovirus viraemia in immunocompetent children in the USA and UK, the US Centers for Disease Control and Prevention (CDC) and jurisdictional health departments initiated national surveillance of paediatric acute hepatitis of unknown aetiology. We aimed to describe the clinical and epidemiological characteristics of children identified with hepatitis of unknown aetiology between Oct 1, 2021, and Sept 30, 2022, in the USA and to compare characteristics of those who tested positive for adenovirus with those who tested negative.

METHODS

In this national surveillance investigation in the USA, children were identified for investigation if they were younger than 10 years with elevated liver transaminases (>500 U/L) who had an unknown cause for their hepatitis and onset on or after Oct 1, 2021. We reviewed medical chart abstractions, which included data on demographics, underlying health conditions, signs and symptoms of illness, laboratory results, vaccination history, radiological and liver pathology findings, diagnoses and treatment received, and outcomes. Caregiver interviews were done to obtain information on symptoms and health-care utilisation for the hepatitis illness, medical history, illness in close contacts or at school or daycare, diet, travel, and other potential exposures. Blood, stool, respiratory, and tissue specimens were evaluated according to clinician discretion and available specimens were submitted to CDC for additional laboratory testing or pathology evaluation.

FINDINGS

Surveillance identified 377 patients from 45 US jurisdictions with hepatitis of unknown aetiology with onset from Oct 1, 2021, to Sept 30, 2022. The median age of patients was 2·8 years (IQR 1·2-5·0) and 192 (51%) were male, 184 (49%) were female, and one patient had sex unknown. Only 22 (6%) patients had a notable predisposing underlying condition. 347 patients (92%) were admitted to hospital, 21 (6%) subsequently received a liver transplant, and nine (2%) died. Among the 318 patients without notable underlying conditions, 275 were tested for adenovirus. Of these 116 (42%) had at least one positive specimen, and species F type 41 was the most frequent type identified (19 [73%] of 26 typed specimens were HAdV-41). Proportions of patients who had acute liver failure, received a liver transplant, and died were similar between those who tested positive for adenovirus compared with those who tested negative. Adenovirus species F was detected by polymerase chain reaction in nine pathology liver evaluations, but not by immunohistochemistry in seven of the nine with adequate liver tissue available. Interviews with caregivers yielded no common exposures.

INTERPRETATION

Adenovirus, alone or in combination with other factors, might play a potential role in acute hepatitis among immunocompetent children identified in this investigation, but the pathophysiologic mechanism of liver injury is unclear. To inform both prevention and intervention measures, more research is warranted to determine if and how adenovirus might contribute to hepatitis risk and the potential roles of other pathogens and host factors.

FUNDING

None.

Recent Increase in Incidence of Severe Acute Hepatitis of Unknown Etiology in Children is Associated with Infection with Adenovirus and Other Nonhepatotropic Viruses

OBJECTIVE

To evaluate whether the nature and severity of non-A-E severe acute hepatitis in children noted by the World Health Organization from late 2021 through early 2022 was indeed increased in 2021-2022 compared with prior years.

STUDY DESIGN

We performed a single-center, retrospective study to track the etiology and outcomes of children with non-A-E severe acute hepatitis in 2021-2022 compared with the prior 3-year periods (2018-2019, 2019-2020, and 2020-2021). We queried electronic medical records of children ≤16 years of age with alanine or aspartate aminotransferase levels of >500 IU. Data were analyzed for the periods of October 1, 2021, to May 1, 2022, and compared with the same time periods in 2018-2021.

RESULTS

Of 107 children meeting entry criteria, 82 cases occurred from October to May of 2018-2022. The average annual case number was 16.3 in 2018-2021 compared with a 2-fold increase (to 33) in 2021-2022 (P = .0054). Analyses of etiologies showed that this increase was associated with a higher number of children who tested positive for viruses (n = 16) when compared with the average of 3.7 for 2018-2021 (P = .018). Adenovirus (26.1%) and severe acute respiratory syndrome coronavirus-2 (10.3%) were the most frequently detected viruses in 2021-2022. Despite evidence of acute liver failure in 37.8% of children in the entire cohort and in 47% of those with viral infection, the overall survival rate was high at 91.4% and 88.9%, respectively.

CONCLUSIONS

The number of children with severe acute hepatitis in our center increased from 2021 to May 2022, with a greater frequency of cases associated with adenovirus, yet transplant-free survival remains high.

Common mechanisms in pediatric acute liver failure

Acute liver failure (ALF) is a rare but potentially fatal disease in children. The etiology is multifactorial, including infection, autoimmune, and genetic disorders, as well as indeterminate hepatitis, which has a higher requirement for liver transplantation. Activation of the innate and adaptive immune systems leads to hepatocyte-specific injury which is mitigated by T regulatory cell activation. Recovery of the native liver depends on activation of apoptotic and regenerative pathways, including the integrated stress response (ISR; e.g., PERK), p53, and HNF4α. Loss-of-function mutations in these pathways cause recurrent ALF in response to non-hepatotropic viruses. Deeper understanding of these mechanisms will lead to improved diagnosis, management, and outcomes for pediatric ALF.

Severe acute hepatitis of unknown etiology in children in 2022: A Narrative Review

Severe cases of acute hepatitis have been reported all around the world since 5 April 2022. Common viral hepatitis agents (HAV, HBV, HCV, HDV, and HEV) were ruled out by laboratory investigations, impelling the term "acute non-A-E hepatitis". Common manifestations consist of abdominal pain, jaundice, and vomiting. A highly elevated level of liver enzymes was a remarkable laboratory finding among the patients. Currently, there is no clear etiology and thus treatment for the condition. Adenovirus serotype 41 (ad-41) was detected in most of the patients even though there is no elucidated link between Adenovirus and acute hepatitis. Other viral agents such as SARS-CoV-2 tested positive in a few cases. Treatment strategies depend on the severity, complications, and sequela of acute hepatitis and can vary widely from supportive therapy to liver transplantation. As of 8 July 2022, 1010 probable cases were reported from 35 countries. More than half were from the European region and were mostly children under the age of 6 years. Among different hypotheses about the etiology of severe acute non-A-E hepatitis, adenovirus-41 is of great importance but further assessments are needed to prove any definite link between ad-41 and severe acute hepatitis.

Severe Acute Hepatitis: An Emerging Grave Illness in Children

Acute hepatitis of unknown origin in children has been recently described in the literature, and a case definition has also been proposed for this condition. The exact etiology is unknown and exclusion of infectious, metabolic, autoimmune and toxin mediated injuries is essential. Management for this condition is supportive, but some may require liver transplantation. Infection prevention and control practices are important as the etiology remains unidentified.

Acute severe non-A-E-hepatitis of unknown origin in children - A 30-year retrospective observational study from north-west Germany

BACKGROUND & AIMS

The etiology of the current acute severe non-A-E hepatitis epidemic in children remains unclear. We aimed to describe the occurrence and outcomes of acute severe hepatitis in pediatric patients in North-West Germany over a period of more than 30 years and in the context of the current epidemic.

METHODS

We analyzed all cases of acute severe hepatitis in childhood, as defined by the World Health Organization, at Hannover Medical School from 1990 and at the University Hospital of Essen from 2009 to 16 May 2022. We separated cases into a historic cohort (1990-2018) and a COVID-19 era cohort (2019-2022).

RESULTS

After application of exclusion criteria, 107 patients with acute severe hepatitis were identified (2.32 cases/center/year). Annual incidence per center rose significantly from 2.2 (historic cohort until 2018) to 4.25/center/year (from 2019, p = 0.002). Of all cases, 75.7% presented with jaundice, while 53.3% had clinical signs of infection. Two cases of adenovirus were proven (2004/2016), other pathogens detected were HHV-6 (4), CMV, HSV, EBV(3). Sixty-nine patients (64.5%) met the criteria of pediatric acute liver failure, with 44 requiring liver transplantation. In the current cohort, patients with infection, gastrointestinal symptoms and higher alanine aminotransferase had a better chance of transplant-free survival, whereas hepatic encephalopathy, higher international normalized ratio and bilirubin predicted a poor outcome. Twenty-five patients developed hepatitis-associated aplastic anemia and 19 patients (17.8%) died.

CONCLUSIONS

Acute non-A-E-hepatitis in children is a rare but severe entity, often leading to acute liver failure. Clinical presentation in our current cohort resembles 2022 NAEH cases, with improved outcomes compared to historic controls. The rising incidence of NAEH in our centers since 2019, in the absence of adenoviral infection, indicates other potential triggers of similar NAEH cases.

IMPACT AND IMPLICATIONS

As the current epidemic of severe acute non-A-E-hepatitis cases in children highlights our limited understanding in the field, we aim to describe current cases, characterizing the presentation over time, and defining similarities and discrepancies before and during the COVID-19 pandemic. Our data show a rising incidence of non-A-E-hepatitis cases since the beginning of the COVID-19 pandemic. These cases were not associated with adenoviral infections, suggesting that the recently described accumulation of adenovirus infections in relationship to hepatitis is a new trigger for a known phenomenon, rather than a new disease entity. Therefore, the role of protective isolation and subsequent lack of contact with trivial infections in children during the pandemic should be the subject of further examinations. We expect our data to contribute to a better understanding of severe acute hepatitis in childhood, increased vigilance for this potentially lethal disease beyond the current epidemic, and ultimately improved clinical diagnosis and care.

Acute severe hepatitis outbreak in children: A perfect storm. What do we know, and what questions remain?

During the first half of 2022, the World Health Organization reported an outbreak of acute severe hepatitis of unknown aetiology (AS-Hep-UA) in children, following initial alerts from the United Kingdom (UK) where a cluster of cases was first observed in previously well children aged <6 years. Sporadic cases were then reported across Europe and worldwide, although in most countries incidence did not increase above the expected baseline. There were no consistent epidemiological links between cases, and microbiological investigations ruled out known infectious causes of hepatitis. In this review, we explore the evidence for the role of viral infection, superimposed on a specific host genetic background, as a trigger for liver pathology. This hypothesis is based on a high prevalence of Human Adenovirus (HAdV) 41F in affected children, together with metagenomic evidence of adeno-associated virus (Adeno-associated viruses)-2, which is a putative trigger for an immune-mediated liver injury. Roles for superantigen-mediated pathology have also been explored, with a focus on the potential contribution of SARS-CoV-2 infection. Affected children also had a high frequency of the MHC allele HLA-DRB1*04:01, supporting an immunological predisposition, and may have been vulnerable to viral coinfections due to disruption in normal patterns of exposure and immunity as a result of population lockdowns during the COVID-19 pandemic. We discuss areas of ongoing uncertainty, and highlight the need for ongoing scrutiny to inform clinical and public health interventions for this outbreak and for others that may evolve in future.

Characterization of a Hepatitis Outbreak in Children, 2021 to 2022

Importance

After a cluster of pediatric cases of hepatitis of unknown etiology were identified in Scotland in March 2022, the World Health Organization published an outbreak alert, and more than 1010 probable cases were reported. Some cases progressed to acute liver failure and required liver transplant. Although many patients had positive results for adenovirus on polymerase chain reaction testing from whole blood samples and/or reported recent COVID-19 infection (with or without seropositivity), the precise pathogenesis remains unclear despite the high potential morbidity of this condition.

Objective

To summarize the currently available evidence regarding novel pediatric hepatitis of unknown etiology (or novel hepatitis), encompassing case numbers, testing, management, and outcomes.

Evidence Review

A rapid review of the literature from April 1, 2021, to August 30, 2022, aimed to identify all available published case series and case-control studies of novel hepatitis. The search included PubMed and references and citations of short-listed studies.

Findings

A total of 22 available case series and case-control studies describing 1643 cases were identified, with 120 children (7.3%) receiving liver transplants and 24 deaths (1.5%). Outcome reporting and testing for adenovirus and SARS-CoV-2 was incomplete. Assessment of disease severity and management was mixed and results regarding testing for adenovirus and SARS-CoV-2 were inconsistent for both serological testing and testing of explant or biopsy liver samples. More recent studies suggest a more plausible role for adenovirus and/or adeno-associated virus 2.

Conclusions and Relevance

This systematic review without meta-analysis describes the challenge posed by hepatitis of unknown etiology in terms of investigation and management, with many cases progressing to acute liver failure. The lack of clarity regarding pathogenesis means that these children may be missing the potential for targeted therapies to improve outcomes and avert the need for transplant. Clinicians, immunologists, and epidemiologists must collaborate to investigate the pathogenesis of this novel hepatitis.

Acute Hepatitis of Unknown Etiology Among Young Children: Research Agenda by the ESPGHAN Hepatology Committee

In April 2022, an increased incidence of acute hepatitis cases of unknown etiology among previously healthy children across the United Kingdom was described. Since, more than 270 cases from the United Kingdom and hundreds more from all across the world have been reported. The majority of affected children were younger than 6 years of age. The clinical presentation was nonspecific with diarrhea and vomiting usually preceding the appearance of jaundice, abdominal pain, nausea, and malaise. Approximately 5% have required liver transplantation. An infectious etiology has been considered likely given the epidemiological and clinical features of the reported cases. Between 50 and 60% of the children tested were diagnosed with adenovirus infection although a clear etiological connection has still to be demonstrated. No link with SARS-CoV-2 infection and COVID-19 vaccine was found. What is not clear to date is whether the high number of acute hepatitis cases reported is related to a true increase in incidence or heightened awareness following on from the initial reports from the United Kingdom. The Hepatology Committee of the European Society of Pediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) developed a paper on the current outbreak of acute hepatitis of unknown etiology recognizing its importance and the need of approaching the current situation with a scientifically rigorous approach. The aims of the article are to summarize the current knowledge and to identify the most pertinent issues regarding the diagnosis and management of this condition and the research questions raised.

Acute hepatitis (Non Hepa A-E) of unknown origin among pediatrics

Several clusters and individual cases of acute hepatitis have been reported in the US, Europe and recently in Asia and Central America since October 2021. A laboratory investigation of the common viral hepatitis agents (HAV, HBV, HCV, HDV and HEV) yielded negative results prompting the use of the term "acute non HepA-E hepatitis" to describe this condition. As of 24 June of 2022, WHO have reported 920 probable cases of severe acute hepatitis of unknown origin among pediatrics in 33 countries in five WHO regions. Since the previous reports on 27 May 2022, 270 new probable cases have been increased, including from four new countries, some of whom were also found to be positive for SARS-CoV-2. All the patients showed symptoms such as vomiting, diarrhea, jaundice, and abdominal pain. The patients' liver enzymes were remarkably increased. No connection with SARS-CoV-2 or its vaccine has been found so far. However, the suspected cause is adenovirus, including its genomic variations, because its pathogenesis and laboratory investigations have been positively linked. Until further evidence emerges, hygiene precautions could be helpful to prevent its spread.

Hepatitis of unknown aetiology in children - epidemiological overview of cases reported in Europe, 1 January to 16 June 2022

Following the report of an excess in paediatric cases of severe acute hepatitis of unknown aetiology by the United Kingdom (UK) on 5 April 2022, 427 cases were reported from 20 countries in the World Health Organization European Region to the European Surveillance System TESSy from 1 January 2022 to 16 June 2022. Here, we analysed demographic, epidemiological, clinical and microbiological data available in TESSy. Of the reported cases, 77.3% were 5 years or younger and 53.5% had a positive test for adenovirus, 10.4% had a positive RT-PCR for SARS-CoV-2 and 10.3% were coinfected with both pathogens. Cases with adenovirus infections were significantly more likely to be admitted to intensive care or high-dependency units (OR = 2.11; 95% CI: 1.18–3.74) and transplanted (OR = 3.36; 95% CI: 1.19–9.55) than cases with a negative test result for adenovirus, but this was no longer observed when looking at this association separately between the UK and other countries. Aetiological studies are needed to ascertain if adenovirus plays a role in this possible emergence of hepatitis cases in children and, if confirmed, the mechanisms that could be involved.

Acute severe hepatitis of unknown etiology in children: A mini-review

The emergence of acute, severe non hepA-E hepatitis of unknown etiology (ASHUE) has attracted global concern owing to the very young age of the patients and its unknown etiology. Although this condition has been linked to several possible causes, including viral infection, drugs and/or toxin exposure, the exact cause remains unknown; this makes treatment recommendation very difficult. In this review, we summarize recent updates on the clinical manifestations, complemented with laboratory results, case numbers with the global distribution and other epidemiological characteristics, and the possible etiologies. We also provide the proposed actions that could be undertaken to control and prevent further spread of this hepatitis. Since many etiological and pathological aspects of the acute non hepA-E hepatitis remain unclear, further research is needed to minimize the severe impact of this disease.

Diagnosis, treatment, and prevention of severe acute hepatitis of unknown etiology in children

BACKGROUND

Severe acute hepatitis of unknown etiology in children has recently exhibited a global trend of concentrated occurrence. This review aimed to summarize the current available information regarding the outbreak of severe acute hepatitis and introduce our hospital's previous experiences with the diagnosis and treatment of severe acute hepatitis for reference.

DATA SOURCES

Websites including the UK Health Security Agency, European Centre for Disease Prevention and Control, CDC, WHO, and databases including PubMed/Medline, Cochrane Library, Embase and Web of Science were searched for articles on severe acute hepatitis in children.

RESULTS

As of May 26, 2022, a total of 650 cases have been reported in 33 countries; at least 38 (6%) children required liver transplantation, and nine (1%) died. Cases are predominantly aged between 3 and 5 years old, and there are no epidemiological links among them. The common manifestations are jaundice, vomiting and pale stools. Adenovirus tested positive in most cases, and SARS-CoV-2 and other viruses were detected in a few cases, but virus particles were not found in liver tissue. Adenovirus immunohistochemistry showed immunoreactivity in the intrasinusoidal lumen from some liver samples. The hierarchical treatment includes symptomatic and supportive therapy, management of coagulation disorders and hepatic encephalopathy, artificial liver support, and liver transplantation (approximately 6%-10% of cases require liver transplant).

CONCLUSIONS

The etiology of this severe acute hepatitis in children is not clear. The clinical features are severe acute hepatitis with significantly elevated liver enzymes. Clinicians need to be alert to children with hepatitis.

Acute Hepatitis of Unknown Origin in Children: Early Observations from the 2022 Outbreak

Recent reports of acute hepatitis of unknown origin in previously healthy children have been increasing worldwide. The main characteristics of the affected children were jaundice and gastrointestinal symptoms. Their serum aminotransaminase levels were above 500 IU/L, with negative tests for hepatitis viruses A-E. By 31 May 2022, the outbreak had affected over 800 children under the age of 16 years in more than 40 countries, resulting in acute liver failure in approximately 10%, including at least 21 deaths and 38 patients requiring liver transplantation. There was still no confirmed cause or causes, although there were several different working hypotheses, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), adenovirus serotype 41, or SARS-CoV-2 superantigen-mediated immune cell activation. Here, we review early observations of the 2022 outbreak which may inform diagnosis, treatment, and prevention in the context of an overlapping COVID-19 pandemic.

Trends in Acute Hepatitis of Unspecified Etiology and Adenovirus Stool Testing Results in Children - United States, 2017-2022

In November 2021, CDC was notified of a cluster of previously healthy children with hepatitis of unknown etiology evaluated at a single U.S. hospital (1). On April 21, 2022, following an investigation of this cluster and reports of similar cases in Europe (2,3), a health advisory* was issued requesting U.S. providers to report pediatric cases^† of hepatitis of unknown etiology to public health authorities. In the United States and Europe, many of these patients have also received positive adenovirus test results (1,3). Typed specimens have indicated adenovirus type 41, which typically causes gastroenteritis (1,3). Although adenovirus hepatitis has been reported in immunocompromised persons, adenovirus is not a recognized cause of hepatitis in healthy children (4). Because neither acute hepatitis of unknown etiology nor adenovirus type 41 is reportable in the United States, it is unclear whether either has recently increased above historical levels. Data from four sources were analyzed to assess trends in hepatitis-associated emergency department (ED) visits and hospitalizations, liver transplants, and adenovirus stool testing results among children in the United States. Because of potential changes in health care-seeking behavior during 2020-2021, data from October 2021-March 2022 were compared with a pre-COVID-19 pandemic baseline. These data do not suggest an increase in pediatric hepatitis or adenovirus types 40/41 above baseline levels. Pediatric hepatitis is rare, and the relatively low weekly and monthly counts of associated outcomes limit the ability to interpret small changes in incidence. Ongoing assessment of trends, in addition to enhanced epidemiologic investigations, will help contextualize reported cases of acute hepatitis of unknown etiology in U.S. children.

[The investigation on the acute, severe hepatitis of unknown origin in children]

In April 2022, the United Kingdom notified the World Health Organization (WHO) of an unexpected increase of acute hepatitis of unknown origin in children. Subsequent investigations have found more than 400 cases in more than 20 countries and regions around the world. Although the potential role of adenovirus type 41 in the pathogenesis of these cases is one hypothesis, but it is probably not the only pathogenic factor, and other infectious and non-infectious causes cannot be completely ruled out. For hepatitis caused by non-hepatitis A, B, C, D and E viruses, there is a lack of systematic monitoring and research, and many unknowns still exist. According to the current etiology speculation and epidemiological characteristics of adenovirus in China, cases of acute hepatitis with unknown origin may be found in China in the future. There is also a risk of imported cases. This article systematically sorts out the reports and studies on child acute hepatitis of unknown origin, hoping to attract the attention of pediatric clinicians in China, raise awareness and vigilance, and calmly prepare for possible abnormal situations.

Hepatitis of Unknown Origin and Etiology (Acute Non HepA-E Hepatitis) among Children in 2021/2022: Review of the Current Findings

Several clusters and individual cases of acute hepatitis have been reported in the US, Europe and recently in Asia and Central America since October 2021. A laboratory investigation of the common viral hepatitis agents (HAV, HBV, HCV, HDV and HEV) yielded negative results prompting the use of the term "acute non HepA-E hepatitis" to describe this condition. The cases were characterized by the manifestations of acute hepatitis (abdominal pain, vomiting, diarrhea, jaundice and very high levels of liver enzymes) affecting children with a median age of 3-4 years. The exact underlying etiology has not been revealed yet; however, a leading hypothesis is that an infectious agent is the culprit, underlying cause or a risk factor for acute non HepA-E hepatitis occurrence. So far, laboratory testing has shown the presence of the group F human adenovirus serotype 41 (HAdV-F41) in about three-fourths of the investigated cases. As of 13 May 2022, more than 450 cases were reported worldwide, the majority of which were in the UK (n = 176), the US (n = 109), 13 European countries (at least 103 cases) and in Argentina, Brazil, Canada, Costa Rica, Indonesia, Israel, Japan, Palestine, Panama, Singapore and South Korea. Vigilant surveillance and epidemiologic investigations to identify further cases are warranted to delineate the features of this emergent public health issue. The possible role of environmental and toxic agents including foodborne toxins should also be considered. Specific guidelines for identification of further cases are necessary, particularly in low-income settings where testing for adenoviruses is not considered routinely. A genetic analysis of HAdV-F41 isolates is recommended to assess the potential changes in the virus genome with subsequent possible altered virus behavior. Immunopathogenesis is another possibility that should be evaluated considering the lack of viral structures in liver biopsies of the affected children in the US.