This invention provides a system and method for sterilizing an ISO 594 female Luer fitting and an attached catheter using UV light. An optical plug can be inserted into a female Luer fitting, and UV-C light or a combination of UV-C and UV-A light can be radiated through the optical plug and into the female Luer fitting and attached catheter, thereby sterilizing the fitting and catheter. A sterilizer device can be used to hold the female Luer fitting and catheter, with an optical plug inserted into the female Luer fitting. The sterilizer device can include a UV light source that radiates UV light through the optical plug and into the female Luer fitting and attached catheter. A protective cover can be placed over the optical plug before inserting the optical plug into the female Luer fitting. The protective cover can be disposable.