Person A (male), completely free of any STDs, has penile-vaginal intercourse with person B (female, STD status unknown). 

After 6-8 hours. 

Person A then again engages in intercourse (penile-vaginal, oral) with person C (female, also known to be STD free) 

Please address the following queries - 

1. 

A) What is the risk of infection, to person C from person A, and how would the risk vary by STD? 

B) If any tests are indicated, then when? 

C) What symptoms should person C look out for? 

D) If the risk is negligible/none, For how many hours/days would your answer remain the same as 6-7 hours? 

2. 

A) What are the likely STDs that person A could contract from B? I presume the risk profile would be different from C. 

B) What steps do you recommend for person A. Which all STDs are to be tested and when? 

C) What symptoms should person A look out for? 

3. How does the answer change with the use of condoms? 

4. How does it change if the unknown individual is a commercial sex worker or a not a CSW? 

Thank you

Starting with person A, and presuming that he did not have an STI at the time he interacted with B, the question becomes did she had an STI and how likely was it for a single act of intercourse to result in him becoming infected.  The answer is that it is unlikely that A would be infected.  Most people, including most commercial sex workers do not have STIs and most single exposures do not result in infection.  The most common STIs which might be acquired would be chlamydia or Gonorrhea, each of which, if acquired would cause burning on urination or a urethral discharge,  testing for these infections can be done with a urine test or a penile swab.  Whether or not, if infected, he would be infectious for another partner (C) a few hours later is unclear but probably not because the infecting bacteria need time to grow before the can be transmitted.

C’s risk for infection would be low, as described above. We’re C to become infected, she would most likely be asymptomatic and need testing to find the infection.  Asymptomatic infections however important to discover as the can lead to complications and be transmitted to others.

If A used a condom with B and she happened to be infected, his risk for infection would be close to zero.

Hope this information is helpful.  EWH