HPV and danger/the danger I pose

I’ve been thinking about HPV and danger and, in particular, about the danger I may pose to women, particularly regarding the transmission of HPV. HPV is prevalent: about 45% of men my age are HPV positive (according to the CDC). I’ve always just assumed, given this, that I’m likely HPV-positive.

And, in the world in which I date, there are two norms – one of which is, of late, being eroded:

#1: Vaginal/anal sex always features condoms, except among the “fluid bonded” – typically those in long-term, monogamous (or at least, monogamous as it relates to unprotected intercourse) relationships. [This clearly is less and less of a norm among those who don’t remember when HIV was a death sentence.]

#2: Oral sex never features condoms – except when performed by sex workers. I literally have not had a condom-covered blowjob – or encountered anyone who even vaguely expressed that preference – in over a decade.

So, I wondered, just how risky is that unprotected oral sex I prefer?

Take 1: Crude, general risk

I tried to quantify the risk. I made some assumptions, like condoms reducing the transmissibility of HPV by 70% and, based on something I saw on Perplexity but now can’t find, a 30% chance that any given act of penis-in-vagina sexual intercourse, or oral sex, could transmit the virus if the virus is present.

Using these assumptions, I made a crude model to explore the potential risk people face – and I might represent. For every ten men in my age group, with a 45.2% HPV positivity rate, and assuming 30% of sexual encounters transmit the virus, the model suggested that about 1.5 of those 10 encounters would effectively transmit HPV. With condom use reducing this risk by 70%, the likelihood dropped to 0.41%. This means that, if a woman had protected sex with 24.6 men, one of those encounters would likely result in HPV transmission. Rounding, I estimated that it might take about 25 average (i.e., men who are no more or less likely to be infected than the mean) men for one effective transmission to occur.

Take 2: Thinking a bit more about me

Most of my sexual interactions don’t involve (protected or unprotected) vaginal intercourse but rather, unprotected oral sex. How does oral sex compare to vaginal sex as a transmission vector? If I assume I’m 100% likely to have HPV (conservative/aggressive, given that I’ve never had symptoms, but still…), and if I assume oral sex and penis-in-vagina sex are equally effective at transmitting the virus, then three out of every ten unprotected oral sex encounters could effectively transmit the virus, or I would likely transmit it in 3.3 sexual encounters.

But is that true? Is oral sex as effective a transmission vector?

Turns out, no. The study I cite below, in take 3, found that oral transmission of HPV was not a significant factor. Specifically, the oral cavity and semen were not involved in the transmission of HPV between partners in the observed couples. The study primarily focused on genital and anal transmission routes rather than oral transmission.

Penis-in-vagina sex is more effective at transmitting HPV than oral sex, because the transmission route is skin-to-skin, and much of the genital area (balls, base, pubis) is not covered by a condom.

I also learned: the infection caused by HPV when transmitted to the mouth is different from that caused when transmitted vaginally. While oral HPV still can cause cancer, it’s typically throat cancer, not cervical cancer. I’m not sure if this is better, but it is different. Additionally, my assumption of a 30% transmission rate seems to have been too high, as actual rates are likely lower, which makes sense given the 45% prevalence rate among men my age.

Take 3: Thinking a bit more about transmissibility

I did some more reading, and found an interesting study. This is a study of 25 heterosexual monogamous* couples over 7.5 months.

It found that “the overall rate of HPV transmission from the penis to the cervix” was 4.9/100 person-months (vs. 17.4/100 person-months in the opposite direction). I used Claude and ChatGPT to help me make sense of this study, and what they tell me – which my read of the article suggests is not hallucinatory – is:

The study examines the transmission of human papillomavirus (HPV) in heterosexual monogamous couples. It observed that HPV transmission from females to males was more frequent than from males to females, with the penis shaft being a key source for male-to-female transmission and the cervix and urine being primary sources for female-to-male transmission. The study highlights the role of sexual activity, anatomical sites, and condom use in HPV transmission, suggesting implications for HPV prevention strategies, including vaccination and safe sex practices. The research underscores the complexity and efficiency of HPV transmission between partners. – (ChatGPT provided this summary, which was slightly better than the Claude summary)

I asked a couple of follow-ups of the paper: first, “What is the rate of transmission from HPV-positive men to HPV-negative women according to the study?” ChatGPT responded, “The rate of HPV transmission from HPV-positive men to HPV-negative women, specifically from the penis to the cervix/urine, was reported as 4.9 per 100 person-months of exposure. This rate varied depending on the source site, with higher transmission rates observed when the transmission involved the female anus.” [This is what I reported above.]

My next question: “And is there information provided about oral transmission?” to which ChatGPT replied, “The study found that oral transmission of HPV was not a significant factor. Specifically, the oral cavity and semen were not involved in the transmission of HPV between partners in the observed couples. The study primarily focused on genital and anal transmission routes rather than oral transmission.”

Some high-level thoughts

At this point, I should be clear, if I wasn’t already. I’m not a statistician. I’m not a public health expert. I make no representations as to anything regarding this. I’m pulling numbers out of my ass, just trying to test my gut sense that, as far as occasional unprotected oral sex with me goes, it’s probably pretty high-risk, compared to unprotected oral sex with others, but probably pretty low-risk, compared to more regular protected penis-in-vagina and protected oral sex with more sexually active others. [I’m definitely much less sexually active than almost all of the partners of anyone I’ve been with in recent years.]

So here are my bullet-point qualitative thoughts, at this point (before we get to the math):

• HPV isn’t particularly easy to transmit. If it were, it wouldn’t have infected less than fifty percent of the adult population. [If half the population has it, then, on average, if you had sex with two people, you’d have had sex with one infected person.]
• HPV is harder to transmit orally than it is by penis-in-vagina intercourse. [Hypothesis: as with HIV, saliva is a significant impediment to transmission.]
• HPV passes more easily from women to men than the other way around.
• As among most adult men, I’m probably more likely to be a carrier of HPV (whether orally or genitally) than most. Estimating my likelihood as being 100% seems likely wrong, and off by an order or two of magnitude, but prudent.
• People having sex with me, and comparing unprotected oral with me to protected penis-in-vagina sex in the rest of their life should definitely give some weight to the frequency of sex they have, the volume of partners they have, and the risk of those partners’ being carriers.
• I’m certainly not no-risk but, in the context of the sex lives of most people with whom I have sex, I’m definitely not high-risk, and may be relatively low-risk.

And then, some more math:

Again, the qualifier: this all is pulled out from deep up my ass.

Here’s my logic: the study says the risk of transmission is 4.9/100 person months. If that’s true, then it would take 2,041 person-months to infection, on average, or 170 years. [Intuitively, this seems to me both a lot and a little. I’m not really sure what to do with it.]

And then, I figure, perhaps wildly aggressively, that the median person in the study had two sexual partners and fifteen total incidences of sex per month. And, that incremental sexual partners and incremental sexual acts are equally likely to result in infection. Which almost surely is wrong. But still. If the average person in the study has 30 sexual partner-acts per month, then that suggests that the median partner-acts to infection is a little more than 60,000. This seems way too high to me! I must be doing something very very wrong.

Still.

What I conclude? Risk of transmission in any given encounter is low, and what drives risk, what compounds risk, is number of partners and frequency of sex. Someone who has a lot of sex, all of which is protected with condoms, is, presumably, 70% less likely to be infected over the same number of partners and acts as another. But….

The real math

Here’s some more math. Maybe, in its simplicity, and rounded assumptions, it’s better, and more directionally helpful. It feels intuitively correct to me, and less complicated:

If condoms reduce risk by 70%, a person who has sex with 3 people without condoms faces risk approximately equal to that faced by a person who has sex with 10 people with condoms (as 3 is 70% less than 10).

Said differently: sex with a person without a condom is roughly 3.33 times as risky as sex with a person with a condom. Or, said differently differently, having unprotected sex with a person without a condom is a little less risky than having sex with three people with condoms.

AND… oral HPV is harder to transmit than vaginal HPV. All this is about PIV sex.

Finally

All that said? I hate the idea that I might ever expose anyone to anything as complicated and potentially destructive as HPV. So kids, get your vaccines!

* Who the fuck knows what “monogamous” means in this context. It’s presumably self-reported and un-policed.