These terms are often confused, but they are not inter-changeable. Sexually transmitted infection is the broadest term. All STDs are STIs, but not all STIs are STDs.

Sexually Transmitted Infection: Invasion of and multiplication in bodily tissue by a microorganism (eg, bacterium, virus, protozoan) that is usually (more than half the time) passed from one person to another during initimate bodily contact meant to give or derive sexual gratification.

Sexually Transmitted Disease: Pathology (ie, damage) with or without symptoms secondary to an infection that is usually (more than half the time) passed from one person to another during intimate bodily contact meant to give or derive sexual gratification.

Reviewed by: Jennifer A. Shuford, MD, MPH
Date: October 2008