TRUVADA: Why are we ALL not taking this???!!!!

[trish]

This is my last post in this thread.


I think.

I hate this field. The lay literature, which is supposed to be sufficiently informative as to allow the public to make intelligent decisions regarding their health and safety, is instead so ambiguous that no intelligent decision making is possible. I have explored several different interpretations of what the lay-literature calls risk and effectiveness and constructed two quick and dirty models based on those understandings. But I not comfortable with any of those under understandings.

The CDC reports the risk of HIV transmission through unprotected receptive anal intercourse with an infected partner is 138 out of 10000 exposures. (http://www.cdc.gov/hiv/policies/law/risk.html)

Most recently I interpreted this to mean that the probability of transmission after ten thousand independent exposures was 138/10000. This would mean the probability of transmission from one exposure was very small.

Here’s a second interpretation: The probability of transmission from one single exposure is 138/10000. It’s not quite the literal translation of the CDC’s statement, but the number (to me) seem much more reasonable: the probability (converted to a percent) of transmission from one single exposure is 1.38% .

I going to construct one more model from this understand (and then give it a rest). The only model considers anal receptive intercourse with an infected partner. It compares PrEP with unprotected intercourse.

The probability of surviving a single exposure without getting infected is 98.62%. So the probability of surviving N exposures without getting infected is (0.9862^N)*100%. So finally the probability (in percentage form) of getting infected sometime during a run of N independent exposures is 100 - (0.9862^N)*100. It’s that simple. That’s the model.

If you have sex 1.5 times daily with an infected partner, then the probability of getting infected during the course of one year (that would be 550 exposures) is 100-(0.9862^550)*100 = 99.95%. Not good.

Does PrEP help? According to CDC “In several studies of PrEP, the risk of getting HIV infection was much lower—up to 92% lower—for those who took the medicines consistently than for those who didn’t take the medicines.” (http://www.cdc.gov/hiv/basics/prep.html)

The risk per exposure (as we now are interpreting it) without protection is .0138. 92% of that would be 0.012696. The number that is 92% lower than .0138 is therefore 0.0138-0.012696= .001104. In percentage form that rounds to 0.11%. To summarize: the probability of transmission through a single exposure without protect is 1.38% whereas the probability of transmission through a single exposure when using PrEP is 0.11%. That’s a significant improvement. Therefore, you’re using a PrEP, then probability of avoiding infection through a single exposure is 99.89%.

Let go back to the example where you have sex 1.5 times daily with an infected partner. This time suppose you’re on a PrEP. Then the probability of getting infected during the course of one year (that would be 550 exposures) is 100-(0.9989^550)*100 = 45.41%. Better. But not good.

I cannot find per exposure numbers on the effectiveness of condoms. Let p denote the probability of transmission during a single exposure with an infected partner.

Then if one uses both a PrEP and a condom the probability of transmission through a single exposure is .0011*p; i.e. the probability that both preventative measures fail at the same time. So the probability that one is not infected is 1-.0011*p. The probability of avoiding transmission given N exposures is (1-.0011*p)^N. In particular the probability of surviving a years worth of exposures (during which you’re having sex with a HIV partner an average of 1.5 times daily) is (1-.0011*p)^550. Even if p were as high as 10%, the probability of no transmission by year’s end (in percentage form) would be 94.13%. The probability of transmission by year’s end is therefore 5.87%. So even if the probability of transmission during one exposure using a condom alone were as high as 10%, condom use would significantly amplify the protection afforded by a PrEP.


So now I’ve presented three fairly divergent probabilistic models HIV infection based on different possible interpretations of the ambiguous lay literature...in particular different interpretations of “effectiveness” and “risk per exposure”.

Model 1: Post 290 (http://www.hungangels.com/vboard/sho...&postcount=290) and Post 301 (http://www.hungangels.com/vboard/sho...&postcount=301)

Model 2: Post 372 (http://www.hungangels.com/vboard/sho...&postcount=372) and Post 373 (http://www.hungangels.com/vboard/sho...&postcount=373)

Model 3: This post.

Their divergent conclusions should show I’ve no preconceived biases regarding this issue. I just want to answer the question, “If your life partner infected, what are your chances of acquiring the infection sometime through your relationship.” I’m not in this situation myself. It just seemed like a simple problem that anyone should be able to solve. And it is a simple problem and anyone can easily solve it, given just a few numbers: The probability of HIV transmission from a single exposure (dependent on the type of exposure) and the effectiveness per exposure of the various preventative measures available. I have not solved this problem to my satisfaction because I do not know how to find the probability of HIV transmission given a single exposure. I should probably look into the professional literature, but I rather not spend that kind of time. Besides...I'm too embarrassed to continue. (It may look like I’ve already spent some time on this, but not really. It takes more time to write the posts than it does to make the models.)

[Tapatio]

when you engage in risky sex you put yourself at high risk. That's all you have to know. So the question I ask is how much do you want to gamble with your health?

This. And no amount of prophylaxis will protect against risky behavior.

I'm still not convinced that people will take Truvada correctly just because it's important. People with TB- which can also kill- are so bad about taking pills that antibiotics which cured TB in the past are useless against strains that now show resistance to multiple drugs.

Truvada-resistant variants of HIV-1 have already been found. With inconsistent (yet still detectable) use, effectiveness drops to 42%. Effectiveness against a resistant strain, I assume, is zero.

These are currently decent treatments. We shouldn't treat them like charms against risk.

That's how we get SuperClap™.

[Westheangelino]

This. And no amount of prophylaxis will protect against risky behavior.

I'm still not convinced that people will take Truvada correctly just because it's important. People with TB- which can also kill- are so bad about taking pills that antibiotics which cured TB in the past are useless against strains that now show resistance to multiple drugs.

Truvada-resistant variants of HIV-1 have already been found. With inconsistent (yet still detectable) use, effectiveness drops to 42%. Effectiveness against a resistant strain, I assume, is zero.

These are currently decent treatments. We shouldn't treat them like charms against risk.

That's how we get SuperClap™.

You're an idiot. Do you know how many people get TB out of 325+ million in this country?????????????????? Really????????????? That's your comparison?

[Prospero]

Good old westheangelino has found a new cause to trumpet - in support of his passion - after months of proclaiming the joy of Poppers. And of barebacking. Stay well Wes....

[trish]

This post continues the development of Model 3 in Post 381 (http://www.hungangels.com/vboard/sho...&postcount=381).

Why Model 3? Because (given the clarification in http://www.cdc.gov/hiv/basics/prep.html ) Model 1 obviously gets the interpretation of “effective” wrong. Model 2’s interpretation of “risk per exposure” is way to rosey (e.g. p = .0000013896). Indeed, I called this a risky calculation in Post 372 (http://www.hungangels.com/vboard/sho...&postcount=372) because I was wary of the interpretation.

What does Model 3 have going for it?
The interpretation of risk per exposure is straightforward. The CDC reports the risk of transmission for unprotected anal receptive intercourse with an HIV infected partner is 138 per 10000 exposures. Model 3 simply interprets this as: the probability of transmission through one exposure is 138/10000 = 0.0138 = 1.38%. Initially I didn’t go with this interpretation and invented Model 2 instead. Why? Because under this interpretation the probability of transmission after 10000 independent exposures is not 138 chances out of 10000. It was stupid of me to expect it should be. All that one can expect is that 138 be the expected number of transmissions given 10000 independent exposures. And indeed
According to Model 3 the expected number of transmission given 10000 independent exposures 138 (the number measured by the CDC).

So what’s left to do with Model 3 is make a predictive theoretical comparison of PrEP use without condoms to its use with condoms.

The effectiveness of condoms against the transmission of HIV is estimated as being somewhere between 90% to 95% (http://www.ncbi.nlm.nih.gov/pubmed/9141163) Let’s take the average and round down to 92%. This number just happens to be the effectiveness of PrEP as well (http://www.cdc.gov/hiv/basics/prep.html).

We saw in my last post that in the case of receptive anal intercourse with an HIV infected partner the probability of transmission through a single exposure for a person using PrEP alone is 0.11%.

Since both PrEP and Condoms have comparable effectiveness against HIV (both 92%) we can also say that in the case of receptive anal intercourse with an HIV infected partner the probability of transmission through a single exposure for a person using condoms alone is 0.11%.

To make Wes happy we’ll also consider the possibility that Truvada(which is a PrEP) is 99% effective. So let’s see, 1.38 is 99% lower than 138. So (using Wes’s report that Truvada is 99% effective) the risk of transmission (for anal receptive intercourse with an HIV partner) is 1.38 per 10000 exposures; i.e. 0.0138%.

For concreteness, once again suppose there are 100 people, each one with a life-long HIV infected partner with whom they have anal receptive intercourse once or twice a day (say 550 times a year).

If the group is on PrEP alone, then after y years the expected number of infected persons is 100[1-(1-.0011)^(550*y)].

If the group is on Wes’s Truvada alone, then after y years the expected number of infected persons is 100[1-(1-.00013^(550*y)].

If the group is on PrEP and Condoms, then after y years the expected number of infected persons is 100{1-[1-(0.0011)*(0.0011)]^(550*y)}.

Since we’ve been through this a dozen times before I’ll just give a very brief explanation of the last of these. The probability that both the PrEP and the condom fail on the same single exposure is the product of their independent probabilities of failure; i.e. (0.0011)*(0.0011). So [1-(0.0011)*(0.0011)] is the probability that there is no transmission on a single exposure. Consequently [1-(0.0011)*(0.0011)]^(550*y) is the probability of no transmissions after y years. So 1-[1-(0.0011)*(0.0011)]^(550*y) is the probability of at least one transmission before y years are up. Multiply by the group size, in this case 100, to get the expected number of transmission. That’s the quick derivation of the third equation.

So let’s take a look at them. They’re graphed below. Neither form of protection works very well alone. Doubling up a PrEP with condoms has better promise. Condoms can significantly amplify the effectiveness of whatever else you’re using.

Some further points:
Condoms separate the HIV virus from exposure to the PrEP thereby minimizing the risk to the general population of creating resistant strains.

Condoms protect against other STDs as well.

PrEP may have side effects.

Okay. Done. That's my story and I'm stickin' to it.

[Tapatio]

You're an idiot. Do you know how many people get TB out of 325+ million in this country?????????????????? Really????????????? That's your comparison?

The comparison was of MDR (threats multi drug resistant) strains, not of transmission rates.

You missed the entire point of the post because of a failure to understand one sentence.

I'll reserve my assessment of your faculties, though.

[MrBest]

This. And no amount of prophylaxis will protect against risky behavior.

I'm still not convinced that people will take Truvada correctly just because it's important. People with TB- which can also kill- are so bad about taking pills that antibiotics which cured TB in the past are useless against strains that now show resistance to multiple drugs.

Truvada-resistant variants of HIV-1 have already been found. With inconsistent (yet still detectable) use, effectiveness drops to 42%. Effectiveness against a resistant strain, I assume, is zero.

These are currently decent treatments. We shouldn't treat them like charms against risk.

That's how we get SuperClap™.

truvada has side effects

[fred41]

truvada has side effects

I'm not sure side effects would be a major deterrent. I think cost would be though.
We live in a world where, genetic predispositions aside, we have people taking tons of medications... to lower cholesterol, fight type 2 diabetes, lower blood pressure, kill all types of pain ...sometimes minor, when often all it would take is to make simple lifestyle changes such as eating right and exercising.
Hell...I'm sure some of the folks on this site still smoke cigarettes and drink til their livers burst.
(I used to know a dude that had such a fear of HIV that , even though he wasn't getting laid on his own, he would refuse to even consider seeing an escort out of fear. He'd rather not have sex...even though he never stopped talking about it...and he smoked like three packs a day...lol)

Condoms are great. They form a barrier that, when used properly, keep out most bugs....but not everyone can use them. If you can't use them, then your only other option is to simply stop having insertive sex with another human being...or form a monogamous relationship whether you really want to or not.

this may be another answer. I'm not sure I would trust it yet,...probably not. Maybe wait and see some more results...but it could be.

I guess my point of this babbling is - everyone can argue their positions til they're blue in the face, but at the end of the day, how we fuck is a personal decision and proselytizing probably wont change what we do in the bedroom. Everyone's head ticks differently.

It's a good debate though, and there are things to learn from it.

[Westheangelino]

This post continues the development of Model 3 in Post 381 (http://www.hungangels.com/vboard/sho...&postcount=381).

Why Model 3? Because (given the clarification in http://www.cdc.gov/hiv/basics/prep.html ) Model 1 obviously gets the interpretation of “effective” wrong. Model 2’s interpretation of “risk per exposure” is way to rosey (e.g. p = .0000013896). Indeed, I called this a risky calculation in Post 372 (http://www.hungangels.com/vboard/sho...&postcount=372) because I was wary of the interpretation.

What does Model 3 have going for it?
The interpretation of risk per exposure is straightforward. The CDC reports the risk of transmission for unprotected anal receptive intercourse with an HIV infected partner is 138 per 10000 exposures. Model 3 simply interprets this as: the probability of transmission through one exposure is 138/10000 = 0.0138 = 1.38%. Initially I didn’t go with this interpretation and invented Model 2 instead. Why? Because under this interpretation the probability of transmission after 10000 independent exposures is not 138 chances out of 10000. It was stupid of me to expect it should be. All that one can expect is that 138 be the expected number of transmissions given 10000 independent exposures. And indeed
According to Model 3 the expected number of transmission given 10000 independent exposures 138 (the number measured by the CDC).

So what’s left to do with Model 3 is make a predictive theoretical comparison of PrEP use without condoms to its use with condoms.

The effectiveness of condoms against the transmission of HIV is estimated as being somewhere between 90% to 95% (http://www.ncbi.nlm.nih.gov/pubmed/9141163) Let’s take the average and round down to 92%. This number just happens to be the effectiveness of PrEP as well (http://www.cdc.gov/hiv/basics/prep.html).

We saw in my last post that in the case of receptive anal intercourse with an HIV infected partner the probability of transmission through a single exposure for a person using PrEP alone is 0.11%.

Since both PrEP and Condoms have comparable effectiveness against HIV (both 92%) we can also say that in the case of receptive anal intercourse with an HIV infected partner the probability of transmission through a single exposure for a person using condoms alone is 0.11%.

To make Wes happy we’ll also consider the possibility that Truvada(which is a PrEP) is 99% effective. So let’s see, 1.38 is 99% lower than 138. So (using Wes’s report that Truvada is 99% effective) the risk of transmission (for anal receptive intercourse with an HIV partner) is 1.38 per 10000 exposures; i.e. 0.0138%.

For concreteness, once again suppose there are 100 people, each one with a life-long HIV infected partner with whom they have anal receptive intercourse once or twice a day (say 550 times a year).

If the group is on PrEP alone, then after y years the expected number of infected persons is 100[1-(1-.0011)^(550*y)].

If the group is on Wes’s Truvada alone, then after y years the expected number of infected persons is 100[1-(1-.00013^(550*y)].

If the group is on PrEP and Condoms, then after y years the expected number of infected persons is 100{1-[1-(0.0011)*(0.0011)]^(550*y)}.

Since we’ve been through this a dozen times before I’ll just give a very brief explanation of the last of these. The probability that both the PrEP and the condom fail on the same single exposure is the product of their independent probabilities of failure; i.e. (0.0011)*(0.0011). So [1-(0.0011)*(0.0011)] is the probability that there is no transmission on a single exposure. Consequently [1-(0.0011)*(0.0011)]^(550*y) is the probability of no transmissions after y years. So 1-[1-(0.0011)*(0.0011)]^(550*y) is the probability of at least one transmission before y years are up. Multiply by the group size, in this case 100, to get the expected number of transmission. That’s the quick derivation of the third equation.

So let’s take a look at them. They’re graphed below. Neither form of protection works very well alone. Doubling up a PrEP with condoms has better promise. Condoms can significantly amplify the effectiveness of whatever else you’re using.

Some further points:
Condoms separate the HIV virus from exposure to the PrEP thereby minimizing the risk to the general population of creating resistant strains.

Condoms protect against other STDs as well.

PrEP may have side effects.

Okay. Done. That's my story and I'm stickin' to it.

Wrong. Condoms and Truvada are both effective on their own. THEIR EFFICACY IS BASED ON HOW WEL YOU USE THEM. NO MORE, NO LESS.

[trish]

Wrong. Condoms and Truvada are both effective on their own. THEIR EFFICACY IS BASED ON HOW WEL YOU USE THEM. NO MORE, NO LESS.

Where did I say 92% is not effective? Where did I say that proper and consistent use was not essential in their application. But effectiveness is not a guarantee that one will remain infection free throughout an extended period of use. Those who engage in risky behaviors for longer periods of time are more likely to reap the ill effects of such behavior. Therefore, it behooves those who find themselves confronting an extended period of time engaged therein to coldly consider the probabilities of infection over time (or equivalently over the number of exposures).

Below in chart form is a comparison of the probabilities of HIV transmission. One curve is for a subject using PrEP alone while engaged in receptive anal intercourse with an HIV infected partner for an extended number of exposures. Another curve is for a subject using PrEP alone while engaged in insertive anal intercourse with an HIV infected partner for an extended number of exposures. Another curve illustrates the probability of HIV transmission to a subject using PrEP+Condoms while engaged in receptive anal intercourse with an HIV infected partner for an extended number of exposures. Finally there is a curve describing the same for subject using PrEP+Condoms while engaged in insertive anal intercourse with an HIV infected partner for an extended number of exposures. (Just for reference, if you have sex with an HIV infected partner once or twice a day for average of 550 times a years for 40 years, that amounts to 22000 exposures. The chart goes up to 30000 exposures) Two of the curves quite obviously asymptotically approach a 100% certainty of transmission. Of course the other two curves approach the same asymptote. This is just an expression of the fact already stated, namely that Those who engage in risky behaviors for longer periods of time are more likely to reap the ill effects of such behavior. The crucial question is how quickly do the curves rise. Those two corresponding to a double use of PrEP+Condoms rise most slowly. Indeed the insertive anal curve for PrEP+Condom (red) barely rises to visibility over 30000 exposures!

To help anyone who would like to criticize this model and it’s conclusions, I make all of it’s assumptions explicit in one place...this post.

The model is based upon:

1 one CDC chart, one CDC outreach page

http://www.cdc.gov/hiv/policies/law/risk.html
http://www.cdc.gov/hiv/basics/prep.html

the NCBI publication
http://www.ncbi.nlm.nih.gov/pubmed/9141163

and five assumptions:

2 The probability of HIV transmission via one exposure of a type that carries R risk per ten thousand exposures is simply equal to R/10000; i.e. R is simply the expected number of transmissions out of 10000 exposures. So when the chart says that 138 is the risk out of ten thousand unprotected exposures to receptive anal intercourse with an HIV infected partner, then the probability of transmission through one such exposure is 138/10000.

3 The effectiveness of a preventative strategy is the percentage by which it lowers the risk. (This definition is inherent in the second link above wherein we’re informed “In several studies of PrEP, the risk of getting HIV infection was much lower—up to 92% lower—for those who took the medicines consistently than for those who didn’t take the medicines.”)
So if p is the probability of transmission through one unprotected exposure (of a specified type) with an HIV infected partner, and if E is the effectiveness of a particular preventative measure (usually expressed as a percent), then P=p-(E/100)*p is the probability of transmission using that particular measure via one exposure.

4 If PrEP and used in conjunction with Condoms, then the probability of no transmission via one exposure (of a specified type) is the product of the probability that there is no transmission using PrEP alone with the probability of no transmission using a Condom alone; i.e. transmission requires the simultaneous independent failure of both preventative measures.

5 Transmission over a run of N exposures is a sequence of N independent events. So if P is the probability of acquiring an infection through one exposure (of a given type and using a specified strategy of prevention) with an HIV infected partner, then the probability Q no transmission through that one exposure is 1-P. The probability of no transmission after a run of N exposures is Q to the Nth power (denoted by Q^N). The the probability of at least on transmission after N exposures is 1-Q^N, equivalently 1-(1-P)^N.

6 The rest is arithmetic, which I assume I did correctly.

It would be helpful to the discussion, if you specify which of these items each of your criticisms is addressing.