Hello, some photos of the trees/location could be helpful.  You can send samples of the trees to the MSU Plant and Pest Diagnostic lab for a formal diagnosis.  Information on how, what, where, to send that can be found at : Plant & Pest Diagnostics.

Douglas fir are very susceptible to a couple different needle cast diseases (Swiss needle cast and Rhabdocline).  Here is an article outlying those diseases: The Douglas-Fir Needlecast Blues

From the information you have provided me, that would be my best guess, there your trees have a needlecast disease causing the needles to fall off.  You can see if the tree buds out and puts out some new growth this spring.  if so, you will need to protect those needles from re-infection.  A broad spectrum fungicide, like Chloronathil works well.  Other labeled options include: copper hydroxide, copper sulfate, mancozeb, and thiophanate-methyl. You would want to start your first application at budbreak and do a subsequent application two to three weeks later.  Unfortunately, if this is a needlecast related problem, you will need to continue doing this preventative application for each future year you would like to keep the trees. 

For general lab related questions, you can the lab at Contact Us - Plant & Pest Diagnostics.  

It's great that you sent in a sample to get a formal diagnosis completed.  Once we have that information we will know more about if other trees would be susceptible. Generally speaking, the needlecast diseases that affect Douglas-Fir, do not impact most other conifers.