Hi I have just noticed a flat(as in it is not raised and cannot be felt)red spot behind my 6 week old daughters knee. It does not disappear when pressure is applied. She has had heat rashes over the last week mainly over her chest neck and back, but at present this is the only red spot like this on her. At present she seems normal in herself. I worry more as I carried strep b during pregnancy. I was treated with iv anti biotics during labour and doctors discussed what to look for with early and late onset infections in baby. As I understood "late onset" was up to 4 weeks after delivery? Is this single spot something to worry about? And if not what could it be?
No you did not have to worry. Isolated red spot without any signs and symptoms is not serious. Your child is also normal and playing so don't worry. As suggested by you the spot is on the back of knee, so possibly it's in the Knee folds. Continues moisture is present due to sweating. Dirt or tiny stool particles in that fold may have created small inflammatory zone due to which there is redness. There can also be the possibility of Mosquito or small insect bite. My advice is to keep the area clean and Chat Doctor.  Wipe the folds with warm water and then apply baby cream.