Those are good questions.  Many people do not get symptoms of sexually transmitted diseases (STDs) even though they are infected.  Symptoms can be a clue or a warning, but may be mild, unnoticeable, or easily mistaken for another type of irritation.  The only way to know if you have been infected with a STD is to get tested. You can get some tests for STDs done any time after having sex or a risk encounter. The culture tests for Chlamydia and gonorrhea can be done very soon after a risk encounter.  It can take up to 3 months after a risk encounter for the blood tests for syphilis, and hepatitis to be accurate. If you feel like you have been exposed to a STD from a sex partner, the CDC recommends testing.  It might be helpful to discuss your concerns and any risk activities with your doctor or health care provider.  With that information, they can accurately assess your needs and recommend the right tests. We hope this information has been helpful.  Please feel free to contact us if you need further assistance. JKA#285 CDC's National Prevention Information Network
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    那天我写信问CDC关于高危后什么时候做性病检查比较准确，这是他们回答的中文翻译： 这些问题提得很好。许多人就算染上了性病也不会有任何症状。症状只能做为一种暗示或警告，但有时会很轻微，很难被发现，或者很容易与其他疾病混淆。唯一能确定是否被传染上性病的方法是做测试。 有些性病在性交或者高危后任何时候都能检查出来。衣原体和淋病的传统检查在高危后很短时间内都能进行。为了准确起见，需要在高危后3个月再做梅毒，肝炎的血检。 如果你觉得你可能被性伴侣感染上性病，CDC建议你去做测试。和你的医生或者医疗服务人员讨论你的焦虑和任何高危行为能对你有所帮助。 他们能准确地评估你的需要并且推荐你做相应的测试。