以下是实验室的人回答: 总结就是性传播疾病都是通过性行为。口水也可能传播但是概率很小，只有口水通过性行为或者轻吻方式，共享食物基本不可能。Virtually never. But it depends on the circumstances under which the saliva exchange took place. Did the exchange of saliva involve oral sex, kissing, or sharing food?
If the saliva exchange occurred via oral sex, then yes STDs can be transmitted, but the risk is very low.
Kissing mouth to mouth does not transmit STDs, unless you happen to have syphilitic sores or herpes sores in the mouth. Herpes-1 can be transmitted by kissing, but this strain of Herpes is called “oral herpes” and can be considered as NOT an STD, and is present in about 50% of the world population, and hence this strain of herpes is not considered a big deal.
Sharing drinks/food/utensils does not transmit STDs.
If the saliva exchanged contains blood, then STD transmission might be possible.
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EDIT - POSSIBLE COMPLICATION
Hepatitis B
According to the CDC, hepatitis B virus can be present in saliva, but it is still not believed to be spread by kissing or sharing utensils. However, it can be spread by sharing toothbrushes, as even microscopic amounts of blood can spread the virus.
