Doctors misdiagnose all the time.
Was diagnosed as borderline mentally retarded as child and sent to special school (Wanaka for those who are locals) and within one week in school I was told it was a bad diagnosis, given an IQ test and told I had a 164 IQ).
Was diagnosed with epilepsy in high school and 9 years later told mistake.
Had leg issue with one doctor diagnosing it as 'all in my head' and another with Plantar Facitiis; later diagnose revealed a tumor the size of a golf ball. I went to doctor who said it was a mental issue, dropped copy of results and told him in front of patients and coworkers he was a quack.
Tommy Morrison did not help his case challenging the existence of the virus. He should have challenged the testing which can result in false positives repeatedly in some cases.