Global epidemiological data
As of 26 May 2022, 650 probable cases of acute hepatitis of unknown etiology in children meeting the WHO case definition have been reported to WHO from 33 countries in 5 WHO regions, and 99 other cases are awaiting classification. The majority of reported cases (n=374; 58%) come from the WHO European Region (22 countries), including 222 (34%) from the United Kingdom of Great Britain and Northern Ireland alone. Probable cases and cases awaiting classification have also been reported in the Region of the Americas (n=240, including 216 cases in the United States), Western Pacific Region (n=34), Asia Region East (n=14) and the Eastern Mediterranean Region (n=5). Compared to previous reports of acute hepatitis of unknown etiology in children, cases are clinically more severe and a higher proportion develop acute liver failure at least 38 (6%) children required transplantation, and 9 ( 1%) deaths were reported.
European epidemiological data
According to the latest joint surveillance report from the WHO Regional Office for Europe (EURO) and the European Center for Disease Prevention and Control (ECDC) on cases originating from EU/EEA countries, as of from May 20, 2022:
- Three quarters (75.4%) of cases are under 5 years old.
- Of the 156 cases for which hospital admission information is available, 22 (14.1%) were admitted to an intensive care unit.
- Of the 117 cases for which this information was available, 14 (12%) received liver transplantation.
- Overall, 181 cases were tested for adenovirus, regardless of specimen type, and 110 (60.8%) of them tested positive. The positivity rate was highest in whole blood samples (69.5%).
- Of the 188 cases tested by PCR for SARS-CoV-2, 23 (12.2%) tested positive. SARS-CoV-2 serology results were only available for 26 cases, of which 19 (73.1%) had a positive result.
- Of the 63 cases with data on COVID-19 vaccination, 53 (84.1%) were unvaccinated.
Most of the reported cases appear to be unlinked and extensive epidemiological investigations are underway to identify common exposures, risk factors or links between cases. Two pairs of cases have been reported as epidemiologically linked in Scotland, and linked cases have also been reported in the Netherlands. Therefore, human-to-human transmission cannot be excluded.
An etiology that remains unknown
The etiology of this severe acute hepatitis remains unknown and is under investigation.
- Adenovirus has been found in 75% of cases tested in the UK and of the small number of samples that have been typed so far, a majority have been confirmed for adenovirus type 41. But this virus does not has never been associated with such a clinical picture in healthy children. This question will be clarified by the extension of adenovirus screening to other cases, beyond Europe and the United States, and by the communication of the results of the UKHSA (United Kingdom Health Security Agency) currently underway.
- Adeno-associated virus (or AAV, for adeno associated virus in English) has also been detected in a small number of cases in the UK, but this virus is not usually pathogenic.
- Hypotheses related to side effects of COVID-19 vaccines are currently not supported as most affected children have not received these vaccines.
- Increased susceptibility in young children as a result of lower circulating level of adenovirus during the COVID-19 pandemic, potential emergence of novel adenovirus, co-infection with SARS-CoV- 2 or a complication of a previous SARS-CoV-2 infection, resulting in superantigen-mediated immune cell activation, are mechanisms that have been suggested. These assumptions need to be investigated further.
Source : Promed