Why transmission risk is stated as an annual risk rather than a per-act risk

[optimist]

Why is transmission risk stated as an annual risk rather than a per-act risk? I've seen this question asked frequently, especially by those who engage in casual sex. I wanted to share my thoughts as to why I believe transmission risk is expressed as an annual risk rather than a per-act risk. All of the following is just my opinion, though my conclusions are based on data from well regarded studies.

 

On average, asymptomatic people shed virus 10.2% of the time. Antivirals reduce shedding by a median of 80%. This means the average asymptomatic person on daily antivirals will be highly contagious 0% of the time and mildly contagious 7.5% of the time. However, the infected person will be unaware of when this shedding is occurring. Overall, the female to male transmission risk in such a scenario is 1% per year with regular condom use and 2% per year without condom use. This annual risk is based on having sex 2-3x per week and increases with increased frequency of sex. I assume this is because greater frequency of sex = greater chance of having sex during that 7.5% of shedding time. Perhaps more frequent friction to the infected area with less recovery time plays a role as well, I don't know.

 

On average, symptomatic people shed virus 20.1% of the time. For these people, a higher proportion of shedding occurs immediately before and after outbreaks, so if they get noticeable prodrome symptoms (such as tingling), they can avoid sex during prodrome, and of course during outbreaks, and for 7 days after outbreaks have healed. The rest of the time, their transmission risk is similar to that of asymptomatic people.

 

Additional factors include a partner's vulnerability to infection. If the partner's skin is compromised by recent shaving or some other trauma, vulnerability to infection increases.

 

So in the case of a ONS, for instance, transmission risk can range from no risk at all if no viral shedding is occurring to mild risk if asymptomatic shedding is occurring to moderate risk immediately before and after an outbreak when asymptomatic shedding levels are highest to high risk during an actual outbreak. Then there are additional factors such as a partner's vulnerability to infection.

 

Again, all of this is just my opinion, though it is based on data from well regarded research.

[Katidid]

@optimist I completely agree here with your opinion. Makes perfect sense to me!!! I have a question. Having had this for 35 plus yrs, you would think I would know everything about the H. Asymptomatic means a person showing no symptoms, correct?? So, prior to anti viral, I was symptomatic approximately 5 times per year. So, I guess that means I was symptomatic?? I've been on anti viral for over a year now with zero ob's....does that make me asymptomatic now?? Just not sure of the exacts. I've never passed it on. Also, I have this question you may be able to answer. Skin to skin contact can transmit H, but only while shedding, correct? If you are not shedding and you have skin to skin contact you don't transmit??

[optimist]

@Katidid I agree with most everything you said above, but it's just my opinion. I don't know whether people who are asymptomatic on antivirals would be considered asymptomatic for purposes of guessing overall annual shedding rates. I would think so since the studies show the increased shedding that occurs with symptomatic people is primarily attributed to the times immediately before and after outbreaks, but also possible that is built into the assumption of 80% decrease in shedding, so I'm not sure. Anyway, there is variance among individuals, so even the quoted rates of 10.2 and 20.1 are just averages and will vary person to person.

[Katidid]

Ahh ok, makes sense. Seems there is still so much I don't know.

[butterfly2018]

Thank you for this information! My question is, how does this relate if you had sex a few days before your first outbreak? I don't recall feeling any tingling. The only thing I recall is being sore after the first couple times and thinking it was due to friction and frequency of intercourse the previous night/day before.

 

If we continued to have sex during that sore period but no open sores were present, is that prodrome? It was only sore, it didn't burn when I urinated or anything. At first I noticed redness, a day later it was redness with bumps, then by day 3 it was sores and it burned to use the restroom. I also had shaved about a week before but this was of course before thinking I had this or experienced any symptoms.

 

I'm not really worried about myself but more so my partner. We were unprotected the whole weekend.

 

Thanks