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

Acute Hepatitis of Unknown Origin in Children: Analysis of 17 Cases Admitted to the Bambino Gesù Children's Hospital in Rome

This study described 17 cases of children admitted to the Bambino Gesù Children's Hospital with acute hepatitis of unknown origin between mid-April and November 2022. Following the World Health Organization's working case definition of probable cases, 17 children, with a median age of 2.1 years (interquartile range: 1.0-7.1), presenting with acute hepatitis non-AE, with serum transaminase >500 IU/L, were included in the study. A pre-specified set of microbiological tests was performed on different biological specimens for all pediatric patients. All patients resulted negative for the common hepatotropic viruses. The most common pathogen detected in blood specimens was human-herpes-virus-7 (52.9%). Adenovirus was detected more frequently in stool specimens (62.5%) than in respiratory (20.0%) or blood samples (17.6%). Regarding Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection, one child tested positive two days after admission, while antibodies against spike and nucleoprotein were present in 82.3% of patients. A co-pathogen detection was observed in 94.1% of children. Overall, 16 children recovered without clinical complications, while one patient required liver transplantation. In these cases of acute hepatitis of unknown origin, adenovirus was mainly detected in stool samples. A co-pathogen detection was also frequently observed, suggesting that the etiology of this acute hepatitis is most probably multifactorial.

Liver abnormalities following SARS-CoV-2 infection in children 1 to 10 years of age

OBJECTIVE

Beginning in October 2021 in the USA and elsewhere, cases of severe paediatric hepatitis of unknown aetiology were identified in young children. While the adenovirus and adenovirus-associated virus have emerged as leading aetiological suspects, we attempted to investigate a potential role for SARS-CoV-2 in the development of subsequent liver abnormalities.

DESIGN

We conducted a study using retrospective cohorts of deidentified, aggregated data from the electronic health records of over 100 million patients contributed by US healthcare organisations.

RESULTS

Compared with propensity score matched children with other respiratory infections, children aged 1-10 years with COVID-19 had a higher risk of elevated transaminases (HR (95% CI) 2.16 (1.74 to 2.69)) or total bilirubin (HR (95% CI) 3.02 (1.91 to 4.78)), or new diagnoses of liver diseases (HR (95% CI) 1.67 (1.21 to 2.30)) from 1 to 6 months after infection. Patients with pre-existing liver abnormalities, liver abnormalities surrounding acute infection, younger age (1-4 years) or illness requiring hospitalisation all had similarly elevated risk. Children who developed liver abnormalities following COVID-19 had more pre-existing conditions than those who developed abnormalities following other infections.

CONCLUSION

These results indicate that SARS-CoV-2 may prime the patient for subsequent development of liver infections or non-infectious liver diseases. While rare (~1 in 1000), SARS-CoV-2 is a risk for subsequent abnormalities in liver function or the diagnosis of diseases of the liver.

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.

A Report on a Nationwide Surveillance System for Pediatric Acute Hepatitis of Unknown Etiology in Korea

BACKGROUND

Several cases of pediatric acute hepatitis of unknown etiology related to adenoviral infections have been reported in Europe since January 2022. The aim of this study was to compare the incidence, severity, possible etiology, and prognosis of the disease with those in the past in Korea.

METHODS

The surveillance group collected data between May and November 2022 using a surveillance system. Acute hepatitis of unknown etiology was defined in patients aged < 16 years with a serum transaminase level > 500 IU/L, not due to hepatitis A-E or other underlying causes. For comparison, data from 18 university hospitals were retrospectively collected as a control group between January 2021 and April 2022.

RESULTS

We enrolled 270 patients (mean age, 5 years). The most common symptom was fever. However, the incidence was similar between 2021 and 2022. Liver function test results, number of patients with acute liver failure (ALF), liver transplantation (LT), death, and adenovirus detection rates did not differ between the two groups. None of the adenovirus-positive patients in either group experienced ALF, LT, or death. In the surveillance group, adenovirus-associated virus-2 was detected in four patients, one of whom underwent LT. Patients with an unknown etiology showed significantly higher bilirubin levels, a lower platelet count, and a higher LT rate than patients with a possible etiology.

CONCLUSION

The incidence of pediatric acute hepatitis of unknown etiology and adenovirus detection rate have not increased in Korea.

Clinical epidemiology and disease burden of adenoviral encephalitis in hospitalized children in China: A nationwide cross-sectional study

Importance

Adenovirus encephalitis is a significant infectious disease of the central nervous system that commonly affects children under the age of 5 and has a profound impact on the health of infants and young children throughout China. National multicenter epidemiological studies have significant public health implications.

Objective

This study aims to report the epidemiology of adenovirus encephalitis in hospitalized children in China, providing valuable guidance for clinicians.

Methods

The data utilized in this study were extracted from the comprehensive Futang Update Medical Records database, which comprises discharge medical records collected by 27 tertiary children's hospitals between January 2016 and December 2018 in China. Specifically, the face sheet of discharge medical records encompassed critical sociodemographic variables and basic medical care details.

Results

In this database, a total of 544 children were hospitalized due to adenoviral encephalitis. The male-to-female ratio was 1.62:1, with more boys being affected across different age groups and places of residence. Of the children hospitalized, the highest number of hospitalizations occurred in the 1-3-year age group and the number of hospitalizations decreased each year from 2016 to 2018. The disease exhibits seasonal characteristics with a pronounced peak in the summer months of June and July. While most children (58%) did not have any significant complications, one-third of them developed respiratory complications, including pneumonia and acute bronchitis. The median length of stay for adenoviral encephalitis was 7 days, and the median cost of hospitalization was 2145.56 US dollars.

Interpretation

This study highlights the prevalence of adenovirus encephalitis in hospitalized children in China. Children aged 1-3 years were found to be the main demographic hospitalized due to this condition, with boys being significantly more affected than girls. The seasonal variations of adenovirus encephalitis were also found to be significant. Fortunately, the fatality rate associated with this condition was low, and the prognosis was generally favorable.

Pathogenicity and virulence of human adenovirus F41: Possible links to severe hepatitis in children

Over 100 human adenoviruses (HAdVs) have been isolated and allocated to seven species, A-G. Species F comprises two members-HAdV-F40 and HAdV-F41. As their primary site of infection is the gastrointestinal tract they have been termed, with species A, enteric adenoviruses. HAdV-F40 and HAdV-F41 are a common cause of gastroenteritis and diarrhoea in children. Partly because of difficulties in propagating the viruses in the laboratory, due to their restrictions on growth in many cell lines, our knowledge of the properties of individual viral proteins is limited. However, the structure of HAdV-F41 has recently been determined by cryo-electron microscopy. The overall structure is similar to those of HAdV-C5 and HAdV-D26 although with some differences. The sequence and arrangement of the hexon hypervariable region 1 (HVR1) and the arrangement of the C-terminal region of protein IX differ. Variations in the penton base and hexon HVR1 may play a role in facilitating infection of intestinal cells by HAdV-F41. A unique feature of HAdV-F40 and F41, among human adenoviruses, is the presence and expression of two fibre genes, giving long and short fibre proteins. This may also contribute to the tropism of these viruses. HAdV-F41 has been linked to a recent outbreak of severe acute hepatitis "of unknown origin" in young children. Further investigation has shown a very high prevalence of adeno-associated virus-2 in the liver and/or plasma of some cohorts of patients. These observations have proved controversial as HAdV-F41 had not been reported to infect the liver and AAV-2 has generally been considered harmless.

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.

Liver abnormalities following SARS-CoV-2 infection in children under 10 years of age

Objective

Beginning in October 2021 in the US and elsewhere, cases of severe pediatric hepatitis of unknown etiology were identified in young children. While the adenovirus and adenovirus-associated virus have emerged as leading etiologic suspects, we attempted to investigate a potential role for SARS-CoV-2 in the development of subsequent liver abnormalities.

Design

We conducted a study utilizing retrospective cohorts of de-identified, aggregated data from the electronic health records of over 100 million patients contributed by US health care organizations.

Results

Compared to propensity-score-matched children with other respiratory infections, children aged 1-10 years with COVID-19 had a higher risk of elevated transaminases (Hazard ratio (HR) (95% Confidence interval (CI)) 2.16 (1.74-2.69)) or total bilirubin (HR (CI) 3.02 (1.91-4.78)), or new diagnoses of liver diseases (HR (CI) 1.67 (1.21-2.30)) from one to six months after infection. Patients with pre-existing liver abnormalities, liver abnormalities surrounding acute infection, younger age (1-4 years), or illness requiring hospitalization all had similarly elevated risk. Children who developed liver abnormalities following COVID-19 had more pre-existing conditions than those who developed abnormalities following other infections.

Conclusion

These results indicate that SARS-CoV-2 may prime the patient for subsequent development of liver infections or non-infectious liver diseases. While rare (~1 in 1,000), SARS-CoV-2 is a risk for subsequent abnormalities in liver function or the diagnosis of diseases of the liver.

What is already known on this topic

Clusters of severe hepatitis in children in 2022 coincident with the increase in COVID-19 infections in children raised the question of the contribution of SARS-CoV-2 to the hepatitis outbreak, though it was soon determined that SARS-CoV-2 was not the primary etiologic agent.

What this study adds

SARS-CoV-2 may prime the patient for subsequent development of liver infections or non-infectious liver diseases.

How this study might affect research practice or policy

Despite the mild initial disease in children, there may be longer term consequences of COVID-19, such as liver abnormalities, that warrants further investigation.

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.

Signatures of AAV-2 immunity are enriched in children with severe acute hepatitis of unknown etiology

Severe acute hepatitis of unknown etiology in children is under investigation in 35 countries. Although several potential etiologic agents have been investigated, a clear cause for the liver damage observed in these cases remains to be identified. Using VirScan, a high-throughput antibody profiling technology, we probed the antibody repertoires of nine cases of severe acute hepatitis of unknown etiology treated at Children's of Alabama and compared their antibody responses with 38 pediatric and 470 adult controls. We report increased adeno-associated dependoparvovirus A (AAV-A) breadth in cases relative to controls and adeno-associated virus 2 (AAV-2) peptide responses that were conserved in seven of nine cases but rarely observed in pediatric and adult controls. These findings suggest that AAV-2 is a likely etiologic agent of severe acute hepatitis of unknown etiology.

National Surveillance of Pediatric Acute Hepatitis of Unknown Etiology, Japan, October 2021-December 2022

Pediatric acute hepatitis of unknown etiology has been reported globally since April 2022. In Japan, 139 possible cases with onset dates after October 2021 were reported as of December 2022. Three patients required liver transplants, but none died. Rates of adenovirus positivity (11/125, 9%) were lower than those for other countries.

Multiplex MinION sequencing suggests enteric adenovirus F41 genetic diversity comparable to pre-COVID-19 era

Human adenovirus F41 causes acute gastroenteritis in children, and has recently been associated with an apparent increase in paediatric hepatitis of unknown aetiology in the UK, with further cases reported in multiple countries. Relatively little is known about the genetic diversity of adenovirus F41 in UK children; and it is unclear what, if any, impact the COVID-19 pandemic has had on viral diversity in the UK. Methods that allow F41 to be sequenced from clinical samples without the need for viral culture are required to provide the genomic data to address these questions. Therefore, we evaluated an overlapping-amplicon method of sequencing adenovirus genomes from clinical samples using Oxford Nanopore technology. We applied this method to a small sample of adenovirus-species-F-positive extracts collected as part of standard care in the East of England region in January-May 2022. This method produced genomes with >75 % coverage in 13/22 samples and >50 % coverage in 19/22 samples. We identified two F41 lineages present in paediatric patients in the East of England in 2022. Where F41 genomes from paediatric hepatitis cases were available (n=2), these genomes fell within the diversity of F41 from the UK and continental Europe sequenced before and after the 2020-2021 phase of the COVID-19 pandemic. Our analyses suggest that overlapping amplicon sequencing is an appropriate method for generating F41 genomic data from high-virus-load clinical samples, and currently circulating F41 viral lineages were present in the UK and Europe before the COVID-19 pandemic.

Acute liver failure and unique challenges of pediatric liver transplantation amidst a worldwide cluster of adenovirus-associated hepatitis

Investigation into a recent cluster of acute hepatitis in children from the southeastern United States identified human adenovirus (HAdV) DNAemia in all 9 cases. Molecular genotyping in 5 of 9 (56%) children identified HAdV type 41 in all cases (100%). Importantly, 2 children from this cluster progressed rapidly to pediatric acute liver failure (PALF) and required liver transplantation. HAdV type 41, a known cause of self-limited gastroenteritis, has not previously been associated with severe cholestatic hepatitis and liver failure in healthy children. Adenovirus polymerase chain reaction assay and sequencing of amplicons performed on DNA extracted from formalin-fixed, paraffin-embedded liver tissue also identified adenovirus species F (HAdV type 40 or 41) in these 2 children with PALF. Transplant considerations and successful liver transplantation in such situations remain scarce. In this report, we describe the clinical course, laboratory results, liver pathology, and treatment of 2 children with PALF associated with HAdV type 41, one of whom developed secondary hemophagocytic lymphohistiocytosis. Their successful posttransplant outcomes demonstrate the importance of early multidisciplinary medical management and the feasibility of liver transplantation in some children with PALF and HAdV DNAemia.

Concurrent infections of cells by two pathogens can enable a reactivation of the first pathogen and the second pathogen's accelerated T-cell exhaustion

When multiple intracellular pathogens, such as viruses, bacteria, fungi and protozoan parasites, infect the same host cell, they can help each other. A pathogen can substantially help another pathogen by disabling cellular immune defenses, using non-coding ribonucleic acids and/or pathogen proteins that target interferon-stimulated genes and other genes that express immune defense proteins. This can enable reactivation of a latent first pathogen and accelerate T-cell exhaustion and/or T-cell suppression regarding a second pathogen. In a worst-case scenario, accelerated T-cell exhaustion and/or T-cell suppression regarding the second pathogen can impair T-cell functionality and allow a first-time, immunologically novel second pathogen infection to escape all adaptive immune system defenses, including antibodies. The interactions of herpesviruses with concurrent intracellular pathogens in epithelial cells and B-cells, the interactions of the human immunodeficiency virus with Mycobacterium tuberculosis in macrophages and the interactions of Toxoplasma gondii with other pathogens in almost any type of animal cell are considered. The reactivation of latent pathogens and the acceleration of T-cell exhaustion for the second pathogen can explain several puzzling aspects of viral epidemics, such as COVID-19 and their unusual comorbidity mortality rates and post-infection symptoms.

Acute hepatitis of unknown origin in children: A combination of factors

On 5 April 2022, the World Health Organization was notified of 10 cases of severe acute hepatitis of unknown etiology in children under 10 years of age in the United Kingdom. Although the exact cause of a proportion of pediatric acute hepatitis and acute liver failure cases was unclear, the above event has caused widespread concern worldwide. As of 14 September 2022, approximately 1,296 probable cases of acute hepatitis of unknown etiology have been reported from 37 countries/regions, of which approximately 55 required or received liver transplantation and 29 died. Although the etiology of acute hepatitis of unknown origin in children remains unclear, many hypotheses have been proposed about the disease. Instead of individual factors such as "adenovirus infection," "SARS-CoV-2 related," and "Adeno-associated virus 2 with helper virus coinfection," it is more likely due to a combination of factors. Accordingly, there is an urgent need for more data and research to clarify the disease etiology. This review aims to provide a historical perspective of acute hepatitis of unknown etiology in children in the past decades and summarize the current hypothesis and evidence on this emerging disease.

Use of Cidofovir for Safe Transplantation in a Toddler with Acute Liver Failure and Adenovirus Viremia

BACKGROUND

Since October 2021, there have been more than 500 cases of severe hepatitis of unknown origin in children reported worldwide, including 180 cases in the U.S. The most frequently detected potential pathogen to date has been adenovirus, typically serotype 41. Adenovirus is known to cause a self-limited infection in the immunocompetent host. However, in immunosuppressed individuals, severe or disseminated infections may occur.

METHOD

We present the case of a two-year-old female who presented with cholestatic hepatitis and acute liver failure (ALF). Work up for etiologies of ALF was significant for adenovirus viremia, but liver biopsy was consistently negative for the virus. The risk for severe adenoviral infection in the setting of anticipated immunosuppression prompted us to initiate cidofovir to decrease viral load prior to undergoing liver transplantation.

RESULT

Our patient received a successful liver transplant, cleared the viremia after 5 doses of cidofovir, and continues to maintain allograft function without signs of infection at the time of this report, 5 months posttransplant.

CONCLUSION

Recent reports of pediatric hepatitis cases may be associated with adenoviral infection although the exact relationship is unclear. There is the possibility of the ongoing SARS-CoV-2 environment, or other immunologic modifying factors. All patients presenting with hepatitis or acute liver failure should be screened for adenovirus and reported to state health departments. Cidofovir may be used to decrease viral load prior to liver transplantation, to decrease risk of severe adenoviral infection.

Acute hepatitis of unknown aetiology among children around the world

By 26 August 2022, the number of cases of acute hepatitis of unknown etiology (AHUA) has drastically increased to 1115 distributed in 35 countries that fulfill the World Health Organization definition. Several hypotheses on the cause of AHUA have been proposed and are being investigated around the world. In the recent United Kingdom (UK) report, human adenovirus (HAdV) with adeno-associated virus (AAV) co-infection is the leading hypothesis. However, there is still limited evidence in establishing the causal relationship between AHUA and any potential aetiology. The leading aetiology continues to be HAdV infection. It is reported that HAdV genomics is not unusual among the population in the UK, especially among AUHA cases. Expanding the surveillance of HAdV and AAV in the population and the environment in the countries with AUHA cases is suggested to be the primary action. Metagenomics should be used in detecting other infectious pathogens on a larger scale, to supplement the detection of viruses in the blood, stool, and liver specimens from AUHA cases. It is useful to develop a consensus-specific case definition of AHUA to better understand the characteristics of these cases globally based on all the collected cases.

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.

Interim Analysis of Acute Hepatitis of Unknown Etiology in Children Aged <10 Years - United States, October 2021-June 2022

On April 21, 2022, CDC issued a health advisory^† encouraging U.S. clinicians to report all patients aged <10 years with hepatitis of unknown etiology to public health authorities, after identification of similar cases in both the United States (1) and Europe.^§ A high proportion of initially reported patients had adenovirus detected in whole blood specimens, thus the health advisory encouraged clinicians to consider requesting adenovirus testing, preferentially on whole blood specimens. For patients meeting the criteria in the health advisory (patients under investigation [PUIs]), jurisdictional public health authorities abstracted medical charts and interviewed patient caregivers. As of June 15, 2022, a total of 296 PUIs with hepatitis onset on or after October 1, 2021, were reported from 42 U.S. jurisdictions. The median age of PUIs was 2 years, 2 months. Most PUIs were hospitalized (89.9%); 18 (6.1%) required a liver transplant, and 11 (3.7%) died. Adenovirus was detected in a respiratory, blood, or stool specimen of 100 (44.6%) of 224 patients.^¶ Current or past infection with SARS-CoV-2 (the virus that causes COVID-19) was reported in 10 of 98 (10.2%) and 32 of 123 (26.0%) patients, respectively. No common exposures (e.g., travel, food, or toxicants) were identified. This nationwide investigation is ongoing. Further clinical data are needed to understand the cause of hepatitis in these patients and to assess the potential association with adenovirus.

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.