Versatile - Anonymous Interpretation:
Psychological / emotional perspective: For an epidemic / plague to take hold people would need to be capable of being contaminated. From an emotional perspective in dreams an epidemic might suggest some kind of group hysteria.
Material aspects: To dream of an epidemic suggests that we are under some pressure, perhaps to maintain our own viewpoint or integrity in the light of group pressure.
Spiritually an epidemic constitutes a generalized plague, infection or contamination of ideas and concepts.