The rare virus suspected of sickening over 1,000 kids can start out like the common cold but quickly evolve into something much more serious, health officials say.

The virus, known as enterovirus 68, is similar to the rhinovirus that causes the common cold, according to the CDC. But unlike a cold, the infection can lead to severe respiratory symptoms like wheezing.

“It’s the wheezing you have to watch out for,” said ABC News’ chief health and medical editor, Dr Richard Besser, referring to the whistling sound generated when air moves through narrowed breathing tubes.

Here are five things you should know about the outbreak:

  • This isn’t the first enterovirus 68 outbreak in the US
  • No one knows how it started
  • No one knows how it spreads
  • There’s no specific treatment
  • Some people may be more vulnerable than others