Yes, a lot of us first came down with a flu-like illness, and were never really well again.
Still, it may or may not be true that a virus continues to be involved in the disease long term. It could be that that virus somehow tips our immune system over the edge and then it continues to behave erratically from there on.
No-one really knows which of these alternatives is true. Recently, I've become more convinced now for the immune system account, because it seems that many different types of infections can trigger MECFS, and the symptoms of the MECFS tend to look similar regardless of the infection that triggered it. That to me suggests something is generally going awry in the immune system that is not virus-specific.
It does seem that some types of infections are more likely to 'trigger' MECFS than others. EBV and Polio, and people are now reporting lots of cases after zika virus. But there are still lots of roads that lead to Rome.
I just thought I'd mention this, because if we take into account this alternative possibility too, it makes the argument stronger.