www.ratguide.com There are some very good articles on pneumonia, Sendai and SDA.

Rats just don't all of a sudden get sick like this without an outside vector bringing something in, especially since it's such a large group that is getting sick. It sounds respiratory in nature since CC had congestion.

Where are the rats kept? Is it possible a wild mouse or something could have gotten in the basement? Wild rodents are known to carry alot of disease and parasites.

Have any new, unquarantined rats been brought in at where you work?