Indeterminate pediatric acute liver failure: Clinical characteristics of a temporal cluster of five children in the Netherlands in the spring of 2022

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.

Outbreak of indeterminate acute liver failure in children with adenoviraemia - Not a new disease

BACKGROUND & AIMS

In the year 2022, an outbreak of indeterminate acute hepatitis and indeterminate paediatric acute liver failure (ID-PALF) in association with adenoviraemia in immunocompetent children was reported in the UK. We postulate that this association is not a new disease in immunocompetent children.

METHODS

Children with acute hepatitis during the outbreak who were referred to King's College Hospital, London for advice and management were included in the study. Data on the frequency of ID-PALF in 2022, as well as transplantation rates and the association with adenovirus infection, were obtained from electronic health records. The clinical presentation, histology and outcomes of children with ID-PALF and adenoviraemia in 2017-2021 were compared with those in 2022.

RESULTS

From January to June 2022, 65 patients with acute hepatitis were referred. Ten children were admitted with ID-PALF. ID-PALF constituted 26% of all PALF cases in 2017-2021, in contrast to 58.8% during the 2022 outbreak. During the outbreak, adenoviraemia was present in 52% of children with acute hepatitis without liver failure (in whom adenoviraemia test results were available) and in 100% of ID-PALF cases. Adenoviraemia was seen in immunocompetent children in 6/13 (46%) of all ID-PALF cases between 2017-2019, with a clear absence of adenoviraemia in the 6 ID-PALF cases during 2020-2021. Compared to ID-PALF with adenoviraemia in 2017-2019 (n = 6), ID-PALF with adenoviraemia during the outbreak (n = 10) was associated with more frequent hepatic encephalopathy, hypotension requiring vasoactive medications and higher plasma ammonia levels (admission and peak), with similar native liver survival.

CONCLUSIONS

The recent outbreak of ID-PALF with adenoviraemia in immunocompetent children does not appear to be a new disease, contrary to perception and other reports. The frequency of such cases over the years could be linked to background rates of adenovirus infections.

IMPACT AND IMPLICATIONS

Indeterminate paediatric acute liver failure (ID-PALF) associated with adenoviraemia in immunocompetent children is not a new disease specific to 2022. The exclusive role of human adenovirus infection in the causation of this outbreak of acute hepatitis seems unlikely. Indeed, we provide histological data from explants in transplanted patients that do not support direct viral cytotoxicity. The disease is probably mediated by immunological injury directed towards adenovirus infection and/or adeno-associated virus-2.

Orchestrated regulation of immune inflammation with cell therapy in pediatric acute liver injury

Acute liver injury (ALI) in children, which commonly leads to acute liver failure (ALF) with the need for liver transplantation, is a devastating life-threatening condition. As the orchestrated regulation of immune hemostasis in the liver is essential for resolving excess inflammation and promoting liver repair in a timely manner, in this study we focused on the immune inflammation and regulation with the functional involvement of both innate and adaptive immune cells in acute liver injury progression. In the context of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic, it was also important to incorporate insights from the immunological perspective for the hepatic involvement with SARS-CoV-2 infection, as well as the acute severe hepatitis of unknown origin in children since it was first reported in March 2022. Furthermore, molecular crosstalk between immune cells concerning the roles of damage-associated molecular patterns (DAMPs) in triggering immune responses through different signaling pathways plays an essential role in the process of liver injury. In addition, we also focused on DAMPs such as high mobility group box 1 (HMGB1) and cold-inducible RNA-binding protein (CIRP), as well as on macrophage mitochondrial DNA-cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway in liver injury. Our review also highlighted novel therapeutic approaches targeting molecular and cellular crosstalk and cell-based therapy, providing a future outlook for the treatment of acute liver injury.

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 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.