Flu tests for symptomatic pts

I have seen many patients who have all symptoms of flu but when tested for flu A and B, it comes back negative. Could it be that they have a strain of flu which we are not testing for or would the A and B tests come back positive despite the strain the pt is infected with? I'm just confused because we stop isolating them when the flu comes back negative and it doesn't seem like we have any further tests we conduct. I just do't get how they could simply have a cold with the symptoms they present with.

Thanks for any help!
We often have pts test negative for flu in the ED, but positive when we test them up in the unit.I've been told it's technique. Though I'd assume the ED knows how to test for flu, I haven't seen them do it. It's not like a MRSA swab. You literally have to be stirring their brains. It's an awful test. I'd almost rather have the flu than be tested for it again.

Technique and there is a high incidence of false negatives. From the CDCFalse-negative (and true-positive) influenza test results are more likely to occur when disease prevalence is high, which is typically at the height of the influenza season.

Quote from delphine22I've been told it's technique. Though I'd assume the ED knows how to test for flu, I haven't seen them do it. It's not like a MRSA swab. You literally have to be stirring their brains. It's an awful test. I'd almost rather have the flu than be tested for it again.