I am not sure my now 6 year old son, Chris got a severe case of RSV when he was 5 weeks old. I also had a 20 month at home with a "cold" My 20 month old, Gary was never tested for RSV because he wasn't in distress.
Chris got it again when he was 2 1/2 years old and it was the middle of summer. my husband had a "cold" any one, from what I was told, can get RSV and it is just a cold but if you are under 2 and a preemie or if your child has certin cardiac issues they are at a higher risk for complications. most people aren't even aware that they or their child have it.
If your child or some one else child it at a higher risk for issues talk to their primary care doctor to see if they qualify for the synagisis shot. it won't prevent RSV but will lesson the effects if the child has one of these issues