When I fell ill with traditional Lyme disease symptoms (flu, fatigue etc ) in 2005 after a deer tick bite, I had 4 negative Elisa tests. My doctors should have treated based on my clinical picture, but did not. I was a mountain bike racer in Lyme endemic Wisconsin, which is why I was even tested. Some people can't even get their doctors to run the test. I was getting ill again in late 2013, which was the start of my neurological and autonomic symptoms, and I had yet another negative Elisa test.

Reasons why tests are negative:

Reasons for False Negative (Seronegative) Test Results in Lyme Disease

Scroll down to the tests section - Reasons for False Negative (Seronegative) Test Results in Lyme Disease

An article by Dr. Cameron why you are supposed to treat based on clinical symptoms:

Relying on a negative Lyme disease test can prove deadly - Daniel Cameron MD