Hello Eric,
For the most part, yes it is. HOWEVER:
1. Pneumonia can be bilateral
2. IPE has been reported in being just unilateral (in combat military swimmers how swim mostly only on one side. The immersed side is the one who got hit with IPE)
Chest films are only part of the puzzle that leads to a diagnosis:
Unfortunately atelectasis, pneumonia and pulmonary edema all can have a similar pattern. However, the diffusion pattern in pneumonia vs pulm edema is different (patchy vs. diffuse). There is a whole lecture on this in radiology rounds.
One would not expect signs of infection in plum. edema associated with IPE. Also, pulm edema with IPE is sudden, pneumonia is not. Etc.
So, one has to take the whole picture into consideration to derive at a viable diagnosis.
Hope this helps,
Claudia R