Compositions comprising miscible blends of antimicrobial bisguanide compounds with certain thermoplastic polymers are provided. These antimicrobial polymeric materials may be further processed into particulate or fiber form for use in fluid treatment devices and processes. The antimicrobial bisguanide compound, such as chlorhexidine, is distributed at the molecular level within at least one thermoplastic polymer, such as a polyolefm, in which the antimicrobial bisguanide compound is soluble to form a miscible blend, which may be from about 1% to about 25% by weight antimicrobial bisguanide compound. The antimicrobial polymeric materials may be secured in a device for antimicrobial treatment of a fluid. The devices may comprise a housing having at least one inlet orifice and at least one outlet orifice, the antimicrobial polymeric material being secured within the house and configured to contact a fluid flowing through the housing between the inlet orifice and the outlet orifice.
