A friend caught chlamydia at University. A lad she had slept with told her he had been diagnosed with it, so she got checked out. She had it vaginally and orally but without symptoms- she would never have know she had it.
She knew she should have used protection but didn't. She was on the pill. She was furious with the lad for giving it to her. Until she followed the clinic advice to tell her previous sexual partners. One man wasn't surprised to be told- he'd had symptoms and gotten treated but not bothered to tell anyone he'd infected! She probably caught it from him. My friend had gone on to infect three people.