an infection that is passed from one person to another during sexual activity (the abbreviation for ‘sexually transmitted infection’) 性传播感染，性行为造成的感染（全写为 sexually transmitted infection） a fact sheet on the symptoms and treatment of STIs 性传播疾病的症状和治疗情况说明书 STIs cause a wide range of illnesses. 性传播感染会引起多种疾病。