Help me quantify just how safe the sex I'm having is
February 3, 2013 1:25 PM   Subscribe

I know the basics, but how can I find out more detail about my personal STI risk so that I can make informed decisions?

Planned Parenthood, the CDC and others have great information about what STIs are out there, their consequences, treatment and how they can be tested for.

What I want to know, but can't find, falls into three general categories:
  1. For different infections, what are the risks of transmission for different kinds of sexual contact (i.e., vaginal, anal, manual, cunnilingus, fellatio all w/ or w/o barriers)?
  2. As a function of time within the incubation period range, how likely is a false negative?
  3. What are the sensitivity and specificity of the different test procedures?
I have found a bit of information for #1. For instance, Planned Parenthood says: "Giving or getting gonorrhea during oral sex is rare, but you can further reduce your risk by using condoms or latex or plastic barriers." But it doesn't quantify how much rarer it is via oral or oral with barriers or where that information comes from.

For #2 and #3, I haven't found any information. I got a great handout from Planned Parenthood that lists the incubation period for different STIs (not on the website, sadly). However, some of the infections I'm most concerned about have really broad incubation periods: 2–12 weeks for HIV and 2–16 weeks for herpes. I'd like to know if there's any information about the accuracy of testing during the incubation period. For instance, if I am tested for HIV 8 weeks after my last sexual contact, is that meaningless, or can I assume some % of certainty? Furthermore, these tests are not perfect even beyond the incubation period, but I can't find any data about how accurate they actually are.

I suppose it's possible that this information just doesn't exist. Maybe the studies haven't been done. But if it is out there, I'd really like to know and be able to read the data myself.
posted by Cogito to Health & Fitness (9 answers total) 7 users marked this as a favorite

STI risk by infection and activity.

You could ask about 2 and 3 at Scarleteen; Heather is a mine of epidemiological data and she just loves to share it; you needn't be a teen.
posted by DarlingBri at 2:36 PM on February 3, 2013 [3 favorites]

One problem with the way you're framing #1 is that it's hard to find data on a per-sex-act basis (i.e. "If I have unprotected vaginal sex with an HIV+ man exactly once, how likely am I to contract HIV?").

At least for HIV, most studies look at couples over a span of time. So the question they answer ends up being more like "If I'm in a relationship with an HIV+ man, and we have unprotected vaginal sex an average-ish number of times in a year, how likely am I to end up contracting HIV by the end of that year?" It's just way easier to gather data like that, so that's what people study.

To find studies like that, a useful search term is "serodiscordant couple." That's public-health-speak for "a couple where one member is HIV+ and the other is HIV- at the start of the study."
posted by Now there are two. There are two _______. at 2:45 PM on February 3, 2013 [3 favorites]

I read a wonderful book by a journalist who did HIV coverage and rubbed elbows with all the greats. Had some kind of provocative title like Wisdom of Whores. In it she described something I have also learned is more or less true, which is that the transmission of HIV to someone who does not have an intravenous drug habit or open sores in their genitalia is very, very low. It would take on average a few hundred rounds of sex for a man to get HIV from a woman, and a dozen for a woman to get HIV from a man. It's not a realistic risk.

HPV as well as herpes; you probably already have it if you've had a decent amount of sex or perhaps even picked it up from your friends or parents.

Herpes is quite scary, certainly, but it's not as big a deal as you would think unless you're pregnant. There's lots of HSV-1 and HSV-2 handwaving in the literature but really it doesn't matter, you could have either and there is no practical difference. It's still quite scary though and I have passed on a few dates when the other person disclosed a history of cold sores. That probably makes me a bad person and my kharmic retribution will likely include a riotous case of genital herpes.

Chlamydia and gonorrhea are mostly curable for now, but you could have it and not have symptoms, and you could unwittingly render yourself infertile if you do, whether male or female. Pelvic Inflammatory Disease I think is the proper term. There is some scary stuff out there about antibiotic resistant types of those two, which frequently come together, and of course make you more susceptible to getting herpes and HIV.

Syphilis is experiencing a delightful resurgence in popularity but is still fairly rare outside of Puerto Rico. When I was there we had some very serious men from the CDC give a series of lectures about being more vigilant as it can have some very scary lyme-disease type lifelong problems if left untreated.

In conclusion, after a lovely decade of medical education and a few years of experience in public health I sort of don't date anymore, but if I did, I would always use condoms but mostly to avoid the much scarier proposition of unintended pregnancy. (I'd like to thank Robin Baker's book Sperm Wars for teaching me that sperm are basically immortal and like to camp out in the crypts of the uterus for a few weeks at a time.)

But to answer your question, sex in the first world is generally quite safe and you likely even with the most reckless behavior would only pick up an embarrassing but only slightly inconvenient problem that would be easily resolved once you saw a doctor.

The real danger for most people is letting an otherwise harmless infection go nuts and develop unhindered because they're ashamed of the stigma.
posted by hobo gitano de queretaro at 3:56 PM on February 3, 2013 [1 favorite]

I read a wonderful book by a journalist who did HIV coverage and rubbed elbows with all the greats. Had some kind of provocative title like Wisdom of Whores.

Yes, the The Wisdom of Whores by Elizabeth Pisani - she's a a former foreign correspondent with Reuters, now a PhD-qualified epidemiologist. It's a marvelous book. It deals more with global HIV policy (ie, the stupid things that governments do which inadvertently increase, rather than decrease the risk of transmission) rather than individual risk, but it's well worth a read.
posted by embrangled at 4:24 PM on February 3, 2013

First, it's not really so hard to find per act transmission risk calculations for HIV. The work has been done. Check this out. And here is an article about estimating the (very low) risk of getting HIV from oral sex.

Second, Wisdom of Whores is a good book, but the author loves to be sensational. Let's be clear, since this is a pretty important issue. The risk of female-to-male transmission is low, but it is not magnitudes lower than the risk of male-to-female transmission. In high-income countries the figures in the linked article are 0.04% and 0.08%, respectively, so men have about half the risk of women all else being equal. Yes, this risk is low, but the idea that women are at vastly greater risk is hooey. And saying it is "not a realistic risk" is, in my opinion, ridiculous. Millions of people get HIV each year globally and tens of thousands each year in the United States, despite the low rate of transmission per sex act. It's worth protecting yourself, Cogito.

Finally, you ask about the window period for HIV and herpes testing. I just wanted to mention the option of getting a PCR HIV test if you are too impatient for the 12 week window period to pass. It can cost more but may be worth inquiring about if you have good insurance coverage.
posted by reren at 4:48 PM on February 3, 2013

First, it's not really so hard to find per act transmission risk calculations for HIV. The work has been done.

I stand corrected. That looks awesome — thanks.
posted by Now there are two. There are two _______. at 5:43 PM on February 3, 2013

In terms of the tests, this is not an easy question - there are different tests that can be done for the various infections and that may be part of the problem in terms of finding the information. It's generally not included in patient information because most people do not understand things like sensitivity and specificity of a test. Not sure how much background you have in this, but basically when you're talking about something like HIV, you usually use two tests - the initial test has a high sensitivity to ensure it catches all the true positives, and the confirmatory test has a high specificity.

Here are links for each infection:
How Accurate is the Urine Testing for Gonorrhea and Chlamydia? Summary: there are multiple types of urine test, but most have high sensitivity and specificity
Screening for gonorrhea: update of the evidence (USPSTF) covers swabs and urine testing. Note that all but the bacterial culture method are combined gonorrhea and chlamydia tests.
HIV testing considerations: covers oral rapid test and pretty much every other type of testing. There is a ton of information here and it is not easy reading for a layperson.
Pap smear versus HPV swab for HPV testing (HPV swab wins by far)
Screening for syphilis infection recommendation statement: RPR or VDRL for screening, FTA-ABS for confirmation
Genital Herpes Infection: Beyond A Clinical Diagnosis. (includes a number of tests that can be done for HSV2)
posted by treehorn+bunny at 10:34 PM on February 3, 2013

A couple of things to keep in mind:

Gonorrhea is increasingly resistant to antibiotics, which complicates what once was a relatively easily-treatable STD.

The Boily article that lists the low chances of being infected with HIV in "high-income countries" is concerned with vaginal heterosexual sex. If you have receptive anal sex the chances of HIV transmission are significantly greater.

Keep in mind that as with any risk assessment, the statistics cut both ways. Air travel is safe, but planes can and do crash, and one is unlikely to feel very good about how rare a plane crash is when one's plane is doing a nose dive.
posted by OmieWise at 9:44 AM on February 4, 2013

A Planned Parenthood physician just discussed false negatives on herpes tests on a recent Dan Savage podcast (stats info starting around minute 8:30). It doesn't directly get to your question of the probability of a false negative during incubation, but it gets at the idea that testing for herpes is not particularly reliable (or rather that the results aren't particularly useful in a practical way).
posted by Terriniski at 6:14 PM on February 5, 2013

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