There has been a recent spike in cases of sudden, severe hepatitis in children around the world. Several news outlets have highlighted a possible link between cases and contacts with pet dogs.
The data suggesting a link is weak and probably a lot weaker than other hypotheses.
In the UK, there was a spike in children's cases of the disease, but it has now been reported in Europe, Asia, and the Americas. Some children have needed a liver transplant because of the severe disease that is still very low.
There are suggestions that it may continue for some time.
Toxicity, such as alcohol, or infections with one of several different viruses, are the most common causes of hepatitis in humans. None of the usual viruses have been found in these children.
The UK Health Security Agency is trying to find the cause of the disease so that it can be controlled and treated.
The agency reported a high number of dog exposures in these cases of severe childhood hepatitis. Before parents stop their children from going near their family dog, it is worth looking at the results in detail.
70 percent of patients were from dog-owning families or had other dog exposures, according to the UKHSA.
Many more children from non-dog-owning households will be exposed to dogs when they visit or play with their friends because 33 percent of households in the UK own dogs. Exposure to dogs may be normal.
It is important to show that exposure to dogs in patients is higher than in unaffected children. Until that is checked in the case-control study, any link is nothing more than a suggestion.
There is a strong chance that the answers to one or more questions may be related to cases, if you ask enough questions.
This kind of spurious association can easily occur where we collect large amounts of data.
There is a website devoted to collecting them. The divorce rate in Maine between 2000 and 2009 seems to be linked to per capita margarine consumption.
There is a spurious association. Tyler Vigen is a person.
The important point is that links are hypotheses. They need to collect more data around new cases. The link will continue to show up in new data if it is real. If it is spurious, it will not.
There is a problem on the spurious-correlation website. Between 2000 and 2009, cheese consumption in the US appears to be linked to deaths as a result of becoming tangled in bedsheets.
It is not hard to think that this might happen because of cheese-related nightmares. Even if the mechanism is far-fetched, the fact that we can think of a mechanism gives us more confidence.
When the evidence is poor, we tend to put more weight on associations where we can think of a reason.
The spike in hepatitis cases in children may be linked to dogs, so what are the possible causes? The adenoviruses has been found in the blood of 72 percent of patients tested, compared to 18 percent for the otherviruses.
Ad41 is a human type that causes diarrhoea in children and was found to be the type where it was possible to identify. Ad41 and the adenoviruses that cause respiratory disease are not known to be associated with dogs.
There are too few cases to suggest that there is an outbreak between children.
The distribution of cases does not suggest that this is a novel virus being transmitted from dogs to children. Cases have appeared in other countries much quicker than a dog virus would.
Is there other possible causes? It has been suggested that the severity of the hepatitis is a result of the immune system malfunctioning.
The transmission of a lot of diseases has been reduced, and a lack of exposure to them may have left some children unprepared for infections that normally wouldn't cause a problem.
The lack of exposure to dirt as a result of hand washing, sterilizing surfaces, and other hygiene measures may cause children to have an over-reactive immune response.
It has been suggested that previous COVID infections may have made children susceptible to the disease.
All of these are theories at the moment, and the data is not enough to suggest control measures or prioritize any of them.
Fortunately, the incidence is still very low, and until there is better data, parents should keep an eye out for any symptoms in their children, rather than reducing their exposure to dogs.
Mick Bailey is a professor at the University of Bristol.
This article is free to use under a Creative Commons license. The original article is worth a read.
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