Dust? Some people are sensitive to dust mite excrement in household dust. Special pillow slip covers and even special mattress covers can tackle that. Some houses with air ducts have filthy with dust air ducts pushing dust around.
Mold (walls? ceiling? basement?) Do you notice a musty basement like smell anywhere? Long term mold spore exposure could be toxic (encouraging asthma?), some types of mold spores are very toxic for even short term exposure (especially for those with weaker immune systems like the elderly and some children).
We had a flood accident and mold started to proliferate behind a wall -- a temporary fix was to run a bedroom HEPA air filter (removed the mold spores from the air very effectively) for a few weeks until the behind the wall area dried and the mold stopped fluorishing and went dormant. I still use that HEPA room filteration unit overnight in my bedroom when our annual pollen season arrives, very helpful.
I think that these are the multiple viral infections that children are so prone to until their immune system develops properly. It may not be quite fare to blame any one house or another child. This is just the way of things and it will get better in time.
You don't run a fever with allergies. While I appreciate your insight, Dr Rynne, let me give a little more information. I stay at home with my child now so she's not constantly exposed to all kinds of other children or homes anymore, we can time this like clockwork. I've actually stopped visiting because of this. I also wasn't 100% convinced the last time it happened, which was also the last time my child had a "cold". This time we visited, maybe there for an hour and half, and like clockwork, she woke a couple days later with another urv. I've tested this theory and I'm convinced, I'm just looking for an explanation and suggestions for what to do, other than stay away. When I was working, they were my babysitter sometimes, as well as another. My child kept getting sick, there would be about a 2 week period between "colds". I couldn't figure out where it was coming from, until I quit work and tested this theory.
I'll also add that the last time I became very sick as well. This time around, not anywhere near as much