As health officials in more than a dozen countries look into the mystery, they are asking:

— Has there been some surge in the stomach bug — called adenovirus 41 — that is causing more cases of a previously undetected problem?

— Are children more susceptible due to pandemic-related lockdowns that sheltered them from the viruses kids usually experience?

— Is there some mutated version of the adenovirus causing this? Or some other not-yet-identified germ, drug or toxin?

— Is it some kind of haywire immune system reaction set off by a past COVID-19 infection and a later invasion by some other virus?