Việc trả lời cụ thể cho từng câu hỏi của em sẽ rất mất thời gian và với câu tâm trạng của em bây giờ anh tin các câu hỏi của em sẽ kéo dài forever và em sẽ không chịu tìm hiểu vì vậy anh sẽ trích dẫn cho em đoạn này. Đấy là câu trả lời của TS BS Hunter Hunsifield về vấn đề này và sẽ không có gì hơn thế.

The reason that some infections are transmitted only by sex, direct blood exposure, and other very intimate contacts (transplantation, childbirth, etc) is that they CANNOT be transmitted by other means.  Why not?  Because large amounts of the causative bacteria or viruses must have direct access to susceptible tissues, which typically are deep inside (gonorrhea, chlamydia, HIV, HBV, etc); or they must be massaged vigorously into susceptible tissues, often with microscopic trauma (syphilis, HSV, HPV).  This is how these bacteria and viruses, and the human interactions with them, evolved over thousands of human generations and millions of years, and it is an essential biological difference between STDs and, say, colds, influenza, common intestinal infections, measles, chickenpox, and a hundred other infectious diseases.

This is why STDs are not transmitted by kissing, hand-genital contact, contact with a contaminated environment, or from such fleeting contact like you describe here -- even fleeting contact with the genitals.  Nobody can say the risk is zero from what you describe.  But in 30+ years in the STD business, I have never seen or heard of such transmission occurring.  The people who show up in the clinic with HIV or other STDs always have had intercourse or direct blood exposure, as through shared injection equipment -- we simply see no exceptions.

So if there is risk in the sort of exposure described in your question, it is far too low to measure or worry about.  This also explains our universal reassurance to questions about mutual masturbation, contact with potentially infected secretions in the environment, and most sexual exposures other than insertive sex.