Loss of Puppies

We've had a very traumatizing experience over the weekend. Libby's 2 5 week old puppies suddenly got sick and died within 12hrs, despite my extensive treatment with medications, fluids, and supportive care. We started the litter on antibiotics on Friday and the remaining puppies acted perfectly fine. Sunday night I found another puppy dead suddenly, and again Monday morning, a puppy who acted fine a few hours before was dead. I took the last puppy to the vet for an emergency IV and antibiotics. They decided to change the type of antibiotic and by yesterday afternoon his condition became grave. He has hung on through the night which is a miracle, so I'm hoping the antibiotics are helping. But it will be a miracle if he survives. We have sent tissue samples to the university for culture and my veterinarians believe it is some type of bacterial infection that has effected the puppy's livers. Since none of my adults or other older puppies are sick, it must have something to do with their immature immunity. It's heartbreaking to have something like this happen, but even worse to tell families just after a happy update and photos, that the puppies have died. I know I'm not in control of nature, but there is just nothing more upsetting than to have something happen and not know the cause. I'm very medically minded and need to know a diagnosis, treatment plan, and how to prevent it and so far no one can tell me anything. It's hard to understand when I'm such a thorough sanitizer, and jokingly call myself a "Germ-phobic", how something could possibly infect my puppies. I sanitize outside with bleach, inside with kennel with vet strength sanitizing solution, and even Dr Gail has commented several times on how clean my place is. The puppies were young enough that although they had been in the puppy house floor and the kids had played with them, they had not been in the yard yet or anywhere that they could have picked up something. It's driving me crazy trying to figure out the how/when/where/why.