Is there a nose swab test for detecting the Swine Flu?

I took my 4 yr old into the doctor 2day, he has a runny nose, fever over 100, vomiting all day, the doctor did a nose swab, said 2 me this is to detect the Swine Flu, which i had no idea they had such a thing. After 2 hours the nurse came into the room & said that it showed up negative, but it doesn't mean that he doesn't have the Swine, but does for sure have a virus. I can accept it being neg. but what the heck do they mean that it still can be the Swine Flu? Is this test not accurate or are they guessing?