This is the 12330th most frequent French word.
épidémique
Relating to or characteristic of an epidemic.
In this usage, 'épidémique' functions as an adjective describing the characteristic of the spread of the flu, indicating it has reached epidemic proportions.
La propagation de la grippe dans cette région est devenue épidémique.
The spread of the flu in this region has become epidemic.
Here, 'épidémique' serves to qualify 'comportements' (behaviors), referring to the nature of these behaviors as related to an epidemic pattern in infectious agents.
Les comportements épidémiques des agents infectieux doivent être compris.
The epidemic behaviors of infectious agents must be understood.
In this instance, 'épidémique' describes the type of risk being discussed, specifically in relation to the possibility of an epidemic occurring.