Some people believe pneumonia spreads quickly, but this past month has shown nothing on earth spreads as fast as an Internet rumour.
Without downplaying its severity, severe acute respiratory syndrome (Sars) has shown technology can be a super-carrier of misinformation that can turn a health scare into a crisis.
The chances of getting Sars in Hong Kong appear to be about one in 9,900. The chance of dying are one in 400,000. But the chance of receiving an e-mail from a doctor whom you have never heard of? A certainty.
The Prince of Wales Hospital, scene of one of the two main clusters of infection in Hong Kong, was also the source of at least part of the panic.
Someone named Dr Jason Fat Wu sent round an e-mail saying we will all get the virus eventually. So why wear a mask? Because that way you can ensure you will get only a small dose of virus rather than a big one. And there we were thinking all viruses were small.
The hospital has done nothing to stem the panic. Its online news section was last updated in November.