WHY? The concept of “disease,” as in STD, implies a clear medical problem, usually some obvious signs or symptoms. But in truth several of the most common STIs have no signs or symptoms in the majority of persons infected. Or they have mild signs and symptoms that can be easily overlooked. So the sexually transmitted virus or bacteria can be described as creating “infection,” which may or may not result in “disease.” This is true of chlamydia, gonorrhea, herpes, and human papillomavirus (HPV), to name a few.