you may want to consider a home daycare that does a full preschool program or does some sort of structured day
I had my daughter in a daycare where I worked until she was 10 months old. She got RSV 3 times. I think an allergy to pears (I nursed and drank pear juice a LOT) may have been a contributing factor, as well as going to the mall for pictures (each incident happened the day after a picture session at picture people - how often do they sanitize the infant stuff?). But I know that daycare was not good for her at the center.
The center I was at did not nap all the babies at the same time, they did not sanitize as often as they should have imo either, partly cause they didn't have a set nap time to do so. At other centers I worked at they had two set napping times in the infant room, every baby napped at that time, and all the toys and surfaces were sanitized at that time, plus at the end of the day. So, not all daycare centers are the same. Perhaps you need to investigate how infant rooms are run at other centers and switch centers.
After I started home daycare my daughter didn't get another lung infection at all even though she was around more kids daily. She also had older kids teaching her how to do things, and later younger kids for her to love and teach herself. I do a full preschool program at my daycare and my older daughter is now in 7th grade getting straight A's. She got a citizenship award in kindergarten, and was ahead of her class all along. So, home daycare may be an option as well.