The meningitis outbreak in Kent has seen 20 confirmed cases. All needed hospital treatment, nine in intensive care. Two young people are dead. This outbreak has been called unusual and unprecedented because of the number infected in such a short space of time. The worst seems to be over with no newly confirmed cases for a week, but there is still an unsolved mystery - why did this outbreak occur? The explanation is critical because it will tell us whether teenagers and young adults are at greater risk of meningitis than previously thought, and whether this was a deeply unlucky one-off or if it could happen again. "That is the million-dollar question," says Dr Eliza Gil, from the London School of Hygiene and Tropical Medicine. We're not facing another Covid. Meningitis is very rare. However, cases of bacterial meningitis do not normally happen like this. Many of us are harmlessly infected with meningococcal bacteria that have the potential to cause disease.…