HIV and related data in Thailand - data driven thread

[hormone]

I thought to post the best information I can find on HIV prevalence/ incidence and epidemiology of transmission in Thailand.  With a relationship obviously to what interests us most, P4P.   The topics of "how many girls have it" and "what's the risk" keep coming back regularly so ... I want this to be a kind of database. 
I have searched over 4 pages of previous threads which brought me back more than a couple of years and haven't found this subject as a stand alone thread. 
This thread is to be data based.  I will try to put as many references as possible.  When I am doing some inferring from data, some hypothetical reasoning, I will state it. 

I DO NOT want this to become a bare backing thread.  I don’t give a hoot if « it’s worth the risk » or not, based on people’s assumptions or on real stats.  All I care about is that people have some FACTS to base their decisions.  I also don’t wish this thread to derail into an STI thread or a PREP thread-- though I might eventually put some info on PREP, as it’s related.
NO opinions,  If you want to take it or not, do as you wish. 

Let's get this out of the way: unprotected sex IS a risk for HIV transmission.  Let’s not try to say « more or less than… ».  Sex with multiple partners increases the risk.  Sex with people who have multiple partners increases the risk.  We'll get back to risk of various situations later.

Now... in Thailand, how many people actually DO have HIV? This site has most updated data from 2023:  https://www.unaids.org/en/regionscountries/countries/thailand
We have to remember that these are estimates, hence there are intervals.  Why?  Because of many things, but mainly because of estimates also of un-diagnosed cases.
For other reasons, it is important to mention that this data ONLY COVERS PEOPLE 15-49 in many cases... Well I don't know if many of us go fuck P4P women over 49 so...
So the oft quoted number of 1,1% of Thailand population is living with HIV is pretty accurate:  take a look... also women vs men...

 

 

 

[hormone]

Thankfully, newborn transmission (vertical transmission) from HIV positive (HIV+) mothers to their babies is uncommon.  Nonetheless there is still about 9 000 new cases of HIV infection diagnosed each year in TH.  Strikingly, men make up a disproportionately high portion of these new infections, with about 80%!   Data still from UNAIDS.org
 

Edited May 20, 2025 by hormone

[hormone]

People are still dying from AIDS in Thailand, but more in TH people are dying of AIDS than people who are getting HIV (boxed data) .  Still, there has been a 65% decrease in AIDS related deaths since 2010 in TH.  Very good news. 
 

This is contrary to world HIV AIDS global statistics (unboxed data)...  Stats still from UNAIDS report.

Edited May 20, 2025 by hormone

[hormone]

It is obviously impossible to know exactly how many people are living with HIV and know of their status, since we don't have totally precise data on number of people who are HIV+...  so the UN does not publish this data.  But at least we know how many people are on anti-retroviral therapy (ART) and we can estimate the best proportion of people who know of their HIV+ status via this number: 82%  -- of which 100% are reported to have suppressed viral loads, which is the most important factor against transmission and progression to AIDS. 

 

Edited May 20, 2025 by hormone

[nagatoro]

52 minutes ago, hormone said:

 

You wonder how there's 4 times as many new infections in men but..

47 minutes ago, hormone said:

 

20% more women die from aids than men.  

That's a quite unexpected and significant difference in the stats you've got there.  Globally med die more often to aids related illness. Wonder whats happened there. Something isn't right with that. Not really possible.

[nagatoro]

Here's an interesting bit from the Asia Pacific regional profile too.

Prostitutes and mongers down.

Gays, trans, drug users and people who have sex with them or who have sex with prostitutes for free up.  

Getting it for free might not be as good people had thought..

[lovermand66]

16 hours ago, nagatoro said:

Here's an interesting bit from the Asia Pacific regional profile too.

Prostitutes and mongers down.

Gays, trans, drug users and people who have sex with them or who have sex with prostitutes for free up.  

Getting it for free might not be as good people had thought..

As i read this, clients of sexworkers are down -65%…
that is good news.
Maybe because many sexworkers are taking pills because they know that they are infected 

[hormone]

On 20/05/2025 at 23:55, nagatoro said:

You wonder how there's 4 times as many new infections in men but..

20% more women die from aids than men.  

That's a quite unexpected and significant difference in the stats you've got there.  Globally med die more often to aids related illness. Wonder whats happened there. Something isn't right with that. Not really possible.

Sorry I have not continued the thread yet, lots of other things on my plate. 
Indeed the much higher rate of new infections in men is quite striking.  I am trying to find some data on that.  I prefer to try to look into possible reasons why it could be possible before saying it's not possible, but I understand the gut reaction! 

For now the logical assumptions I can make (and from some discussions with Thai specialist doctors) is that a lot of young men "screw around" a lot but with a limited amount of women.  In other words, a few women are "shared" without protection by many men.  I know that a high proportion of young thai men also have used commercial sex (up to 25% from what I have found), unsure if this is a reason.  I will try to put up a decent post on all this within 1-2 days. 

About why women die more of AIDS than men: nowadays if you die of AIDS, it is because you have not been properly treated for it.  Given that TH has free HIV ARV treatment for people (with certain strings attached...) it seems to point to some barriers to access to treeatment.  Another logical guess here: could it have in part to do with the fact that to get free ARV treatment you need to go to your "base hospital" (usually the one where you registered in your home town).   Since many women go out of province for sex work, it makes it harder for them to enter these free treatment programs and the disease is allowed to progress.  There could also be a high social stigma related to having HIV (esp. in rural communities) which would result in women diagnosed with it being abandoned...

Edited May 23, 2025 by hormone

[nagatoro]

1 minute ago, hormone said:

Another logical guess here: could it have in part to do with the fact that to get free ARV treatment you need to go to your "base hospital" (usually the one where you registered in your home town).   Since many women go out of province for sex work, it makes it harder for them to enter these free treatment programs and the disease is allowed to progress

I should have thought of that but for whatever reason I didn't.  I don't doubt at all this would be a contributing factor.  Anecdotally, I fucked a girl for a couple of days not long ago and gave her a bunch of money and she said to me she was going to use some of the money to buy anti hiv medicine.  Didn't ask if she was poz or if it was for prep.  Just kind of smiled and was like yes good idea lol

Socially I'm not sure there's much reason a Thai woman vs a Thai man would have any different attitude towards treatments.  Usually it's men that ignore their health.

[hormone]

1 hour ago, nagatoro said:

I should have thought of that but for whatever reason I didn't.  I don't doubt at all this would be a contributing factor.  (...)

Socially I'm not sure there's much reason a Thai woman vs a Thai man would have any different attitude towards treatments.  Usually it's men that ignore their health.

It's not always easy to think of all aspects, for sure. 
I agree with you the usual male/female behaviours always show males are much less careful about health, greater risk takers etc.  But I can see how single moms/ family provider women here have to go away from the village for the sex work vs maybe they guys tend to stay more local?   So for women they get into the immediate dilemma which could be for example : go make money in Pattaya so my family can live next week vs stay in province and get treatment but we can't eat...

[nagatoro]

3 minutes ago, hormone said:

go make money in Pattaya so my family can live next week vs stay in province and get treatment but we can't eat...

Sad to say but yeah, I think that's a real possibility of that unless there's been a serious fuck up with the production of these stats.  4 times the number of men getting it but more women die from it. 

Even considering that recent deaths are of people that were far progressed before modern meds were available and predominantly female sex workers were disproportionately affected the gender disparity is outstanding.  But aye, the Thai women, or maybe more accurately the issan woman bear a hell of a burden whatever the cause.

[hormone]

15 minutes ago, nagatoro said:

Sad to say but yeah, I think that's a real possibility of that unless there's been a serious fuck up with the production of these stats.  4 times the number of men getting it but more women die from it. 

Even considering that recent deaths are of people that were far progressed before modern meds were available and predominantly female sex workers were disproportionately affected the gender disparity is outstanding.  But aye, the Thai women, or maybe more accurately the issan woman bear a hell of a burden whatever the cause.

From my knowledge, I can say that I believe the stats.  For one, they are published by a UN organization, so they would not just take any stats not based on pretty solid methodology.  Of course, there is a grey zone (the not yet diagnosed portion of the population--> more on that later, I promise). 

Another aspect is that quality of care in rural Thailand is VERY variable and often far from being up to par with major university hospitals in big cities.   There is often a fatalistic attitude of "it is what it is" -- a common situation would be for example someone presenting with a terrible illness having an 80% mortality rate, but maybe 20% survival if a successful operation is performed.  In western medicine, usually the doctor will perform the operation (unless the patient is elderly and has not much expected quality of life).   In Asia, I have seen the reverse too many times.... And heard doctors say: "he/ she is likely to die anyway, why spend precious few resources?"  Or also: "If I operate and the patient dies, the family is more likely to blame me for having caused the death... "
I have heard this in Cambodia, Indonesia and Philippines also...

[hormone]

HIV population KNOWLEDGE and SOCIAL STIGMA: since we talked a little about social stigma, I dug more into the topic.  I was ... a bit shocked... at some of the findings.   The first table comes from MICS 2106 of Bangkok area people about HIV

The next data comes from a 2022 UNICEF survey of 30 500 Thais called MICS More details on MICS* lower down...

The 2 most common misconceptions about HIV in Thai population: (MICS 2022 page 87)
1- HIV can be transmitted by sharing food with someone HIV+ : 27-29 % of respondents believe this...
2 - HIV can be transmitted by mosquito bites:  20% of respondents believe this
Also about 15-16% of people do not think a healthy looking person can be HIV +
Notably almost 6-7 % think HIV can be transmitted by supernatural means (!!)
Sadly there is not a huge learning curve as people get older.  The the 40-49 yo group does not perform much better than the 15-24 yo group. 

The total score of people who got all correct (who know that HIV cannot be contracted by sharing food, nor by mosquitoes and that a healthy looking person CAN be HIV +) is only 57% of responders.  Meaning that over 40% of people harbour at least one mistaken idea about HIV transmission. 

About STIGMA and PREJUDICE:

About 28% of people reported discriminatory attitudes towards people HIV + (either would not buy fresh vegetables from a seller HIV + or think HIV + kids should not go to school with other kids)
About 60% of people  think they would hesitate to take an HIV test from fear of how people would react if they were positive!  and 57% of people answered they think HIV+ people lose the respect of other people.
Sadly these numbers seem to stay about the same no matter the level of education, including university graduates.   Rural populations do "worse" for the stigma vs urban. 

*Multiple Indicator Cluster Survey (MICS) in Thailand: done by Unicef to monitor the situation of children and women and track progress towards Millennium and Sustainable Development Goals  Development Goals.  
The full report can be found here:   https://www.unicef.org/thailand/media/11356/file/Thailand MICS 2022 full report (English).pdf ) 
 

[hormone]

HIV TESTING in THAI POPULATION

I also found in MICS 2022 and in MICS 2016 the results showing how many people have gotten HIV tests in the previous year.   Again, I am a little ... surprised (or naive?). 

2022 survey shows that: 

Percentage of people 15-49 yo who know of where to get tested for HIV:
Women: 78%
Men: 71%
Percentage of people 15-49 who had a test in the last 12 months and know their result:
Women: 3,3%
Men: 2,4%

This has gone DOWN from the MICS 2016 survey:

The survey does not differentiate who was currently in a relationship or "free agent" if I can say...
Shockingly, about 25% of women in both surveys who got pregnant were NOT offered an HIV test during prenatal care...

Edited May 23, 2025 by hormone

[hormone]

HIV IN YOUNG THAI MEN:

So the 2023 published data shows that in people age 15-45, there are 42% more HIV+ men vs women (340k vs 240)  and 4 times more new infections in young men vs women (7200 vs 1800).  This seems to be a relatively "recent" phenomenom.  Prevalence of HIV among young Thai (male) army recruits had been stable at 0.5% from 2005 to 2011. But it's on the rise, clearly, now at 1,1%.  Does it seem to be supported by more data?   Yes. 

A 2018 study in military conscripts (males, average 21 yo) had 4629 participants and showed a 1% rate of HIV+ .  Looking into subgroup for transmission risk factors, there were 10% of participants who reported having had at least one MSM sexual encounter, though 97.6% preferred to have sex with females only.  In the MSM group there were 4% HIV+.   The proportion of consistent condom use with a male partner was 39.7%.  Also 21% reported having had sex at least once with a female sex worker.  42% had 6 or more lifetime sexual partners. 
The highest proportion of HIV+ conscripts were from Bangkok and North-East regions, at 1,5% and 1,3% respectively.  

This was voluntary participation so you could potentially suppose the real rate could be higher: people who know they are more likely to be positive/ more at risk could be less inclined to participate in the study, given the Army's very strong "macho" attitude and how NCOs can treat conscripts.  But I digress...

https://www.nature.com/articles/s41598-021-87474-7
 

 

[WhereIsMyMind]

On 24/05/2025 at 18:34, hormone said:

HIV IN YOUNG THAI MEN

Reading even part of that study was mildly infuriating. Maybe it's because I'm not a scientist, but IMO the article did not present the data in any format which is useful to me, and I imagine most people here, but it was likely deemed useful propaganda material for whoever funded it. I really hate this reality of ours. All hail the Matrix.

Key issues/annoyances:

They have a category for FSW (female sex workers), indicating men who have had sex with female sex workers. They DO NOT have a category for MSW (male sex workers). They DO NOT have a category for TFSW/TMSW (Trans Female/Male Sex Workers).

There is no way to determine how many of the non Male-Male sex participants had sex with FSW, nor how many of this group, which we can't determine, are HIV+. The only "data" they have on this comes as another useless statistic: "Having a history of sex with a FSW (AOR: 0.5; 95% CI: 0.2–1.2) was found not to constitute a significant risk factor for HIV infection among the participants." How many of those having a history of sex with FSW ALSO have male-male sex? How many have history of intravenous drug use? If I had raw data I could filter it out myself.

There is no way to correlate between intravenous drug use, male-male sex, prep use, etc., to determine any useful stats on HIV transmission from this set of data which is hidden from us due to privacy concerns.

Basically, it's somewhat useful HIV data (participants were all early 20s, so not ideal by any means) which is presented to us in a manner that's only useful for propaganda purposes.

I HATE IT

Edited May 26, 2025 by WhereIsMyMind

[hormone]

18 hours ago, WhereIsMyMind said:

Reading even part of that study was mildly infuriating.

Key issues/annoyances:

They have a category for FSW (female sex workers)  They DO NOT have a category for MSW (male sex workers). They DO NOT have a category for TFSW/TMSW (Trans Female/Male Sex Workers).

There is no way to determine how many of the non Male-Male sex participants had sex with FSW, nor how many of this group, which we can't determine, are HIV+. The only "data" they have on this comes as another useless statistic: "Having a history of sex with a FSW (AOR: 0.5; 95% CI: 0.2–1.2) was found not to constitute a significant risk factor for HIV infection among the participants." How many of those having a history of sex with FSW ALSO have male-male sex? How many have history of intravenous drug use? If I had raw data I could filter it out myself.

There is no way to correlate between intravenous drug use, male-male sex, prep use, etc., to determine any useful stats on HIV transmission from this set of data which is hidden from us due to privacy concerns.

Basically, it's somewhat useful HIV data (participants were all early 20s, so not ideal by any means) which is presented to us in a manner that's only useful for propaganda purposes.

I get your point!   But I disagree about propaganda.  And also I want to re-iterate I have no hidden agenda for this thread.  Just report what's out there. 
The reasons I picked this study are because: it showed an increasing HIV + over the years, the prevalence was 1% which reflects other published numbers and the prevalence for guys who fit into MSM also reflect other published data.  Finally I thought it was interesting that even though 97.6% preferred to have sex with females only, 10% fit into MSM categorization!   Which can point either at experimentation or opportunity encounters (for example men in prison relate more MSM while in prison, even though they would self-classify as "purely heterosexual" -- in desire). 

This study is a "surveillance" study with the objective of tracking the HIV + rate in a certain population as its primary goal.  They repeat it over time to see trends.  These are far from perfect, indeed. 

Contact with FSW was not deemed significant could simply be attributed to the number of HIV + people found in this sub-group (meaning low total numbers resulting in insufficient detection power statistically) .  As you noted: AOR: 0.5; 95% CI: 0.2–1.2  --> the "odds ratio" (or if you want = risk) has a wide confidence interval (the 0.2-1,2) which when crosses 1 it means it could go both ways as 1 is deemed "neutral" or not influencing.  

[hormone]

BANGKOK AREA  NUMBERS - RED CROSS HIV TEST CENTER in BKK

Quasi real time data can be found here: https://th.aidsid.or.th/

The Thai Red Cross offers rapid walk in HIV testing (and other STI counseling, ARV, PrEP). 
FACT: As of today, numbers from Jan 1st to May 31st 2025 show a 2,4% positivity rate (350/ 14373).

OPINION:  The number/ proportion of positive cases so far this year is worrisome. According to Thai specialists it is on the rise. Here I am talking in a "general population perspective" here, not specifically on a mongering perspective.  Of course, when you know how many young women work/ have worked in the p4p industry at some point in their life... It will be inevitable that the HIV rise in the general population will reflect in the sex workers population.  But remember that all studies show a higher infection rate among the sex worker population. 
POTENTIAL BIASES:  free anonymous testing and Red Cross center (reputation to be less judgmental) might draw people from less privileged environments, or people who are more likely to be positive, more sex workers, more MSM, etc.  I have not found data on the demographics of the center's clientele. 

 

[hormone]

I decided to post here some info from another thread (a bb thread...) as I like to put all interesting data in a single place.  I will a little more detail here.  
As of today, the  2025 Bangkok Red Cross Anonymous clinic data (including up to October 2025) shows a positive HIV test rate of 2,5% = 705 positive tests out of 27 541 tests done.  
Sometimes we tend to call this  "incidence rate" erroneously (or for ease of understanding) as these are all NEW cases.  

1-  It's possible to infer incidence trends from positivity rate when data is very limited as long as you're clear about the limitations of your sample.  Whatever criticism we can have about new HIV+ rates (accuracy) at the BKK Red Cross free clinic we can have for all of Thailand, in either direction.  More on that below.  Another possibility is that the disease is spreading faster.  You need to look at the yearly trends to verify this.  

2- Females getting HIV test @BKK Red Cross clinic make up for about a third of the people: variable results across the years, 34% max.   BUT their test positivity rate seems higher than males!  up to 20-25% (source: personal communication with an infectious disease specialist @ Chula).  BKK Red Cross Clinic is for WALK-IN people, not for prisoners, not for methadone programs, etc. which are also run by Thai Red Cross in collaboration with government.  I did not find a full epidemiological description of the people who go get tested at the BKK Red Cross Anonymous clinic.  
  
3- Remember that all Thais are eligible for free HIV testing 2 times/ year (at government hospitals/ clinics).  Many don't get tested, even if common sense would dictate some of these people should.  This lack of testing is not particular to TH.  

4 -When the positivity rate (i.e. 2,5%) is higher than the prevalence (HIV+ in TH 15-49 yo = about 1%) it can mean that the testing is targeted. You test people who have a higher chance of being positive.   Who are these people?   People with suspicious symptoms.  People with significant exposure history.  Men who have sex with men, sex workers, IV drug users... etc (it does not mean all these people make up the test population at BKK Red Cross).  

But remember we cannot randomly test across the whole Thai population.  There are various national free testing programs but all are voluntary.  For example many pregnant women refuse to get an HIV test, even if it should be included/ offered in their prenatal package.  Some women have told me they have never been offered the test (!!) while others just did not want to do the test.   So again, same criticism of sample bias can apply to all samples...  

5- Reliability of sources/ numbers: exact numbers in Thailand for reported new HIV cases are hard to find.  Even official numbers published by UNAIDS (they take their numbers from Thai Public Health) state a certain variability.  
a) for 2025 many sources state 8862 new cases in Thailand but when you read details it's clear it's a projected figure: this number was published in May 2025, but many sources quoting this number forget to mention it WAS a projection.   At the time, public health authorities were stating the case numbers were higher year on in 2025 vs 2024... and the increase is in <25 yo group. 
b) for 2024: huge variability in numbers that I have seen: between 6-8 000 new cases!  
c) 2022: 9230 new cases in Thailand 
d) The BKK Red Cross Anonymous clinic is one of the most reliably reporting test centers, here are their past results (reference: Thai Red  Cross Society annual report for the given years, published in Thai only) : 
- 2023 : positivity rate of 3,4% -- 1123 cases for 32822 tests
- 2024: positivity rate of 2,7% -- 944 cases for 34917 tests
- 2025 up to October: positivity rate of 2,6% -- 705 cases for 2754 tests

6- Thai data for the CD4 count* on new diagnosis shows that only 14% of people had normal CD4 and >50% have a CD4 count <200 (= definition for AIDS).  This means HIV in TH is often diagnosed at a later stage, after a few years or more, allowing plenty of time to potentially spread the virus before the diagnosis. 
This in part may also explain why mortality rate for HIV+ patients in TH is still high, even if free testing is available and (theoretically) free ARV treatment is also available for all Thais: they start at a more advanced disease stage.  

*CD4+ T-helper cells (we often say CD4 for short) are a kind of white blood cell affected by HIV infection.  HIV infection lowers CD4+ cell count with time; below 500 is abnormal; the low CD4 count contributes to your immune compromise... As HIV infection progresses, your CD4 count decreases...  Usually this means that these people have been HIV+ for a certain amount of time, usually more than a few years.   There is not a clear rate of decrease in CD4+ count vs time associated with HIV infection, but there are some clear trends / general principles.  There is not a clear relationship of CD4 count to infectivity, but infectivity increases as you reach advanced AIDS stages with a higher viral load.  

7- Thailand reports consistently lower HIV rates in female self identified sex workers (SW), but again this sample can be biased in many ways:
- self reporting of being a SW by "regular workers" vs part time or freelancer may not self identify as SW 
- the ones who get tested regularly might be the ones more aware of HIV risk and more likely to use protection (almost) all the time, hence less likely to become HIV+ 
- many sex establishments such as large Thai brothels, kapoo shops, massage shops, etc. have a "policy" of 100% condoms use; I am not saying getting bareback is impossible in these places, far from it, but there is clearly a shop culture of condom use, it's easier for the girl to resist client request/ pressure of not using a condom.  Public health programs also target these establishments.  The young TF FL might be see things differently.  

[navinor]

Thank you @hormone for doing the research!
Just thought I would add some data regarding the actual risk of infection when having sex with someone that is HIV+

The risk varies with viral load of the person that is HIV+, one basic rule is that if the person in well medicated an thus has zero viral load, also known as "U=U"
 https://hivinfo.nih.gov/understanding-hiv/fact-sheets/understanding-hiv-transmission

If you have sex with a person that is not well medicated, the risk obviously increases. How much depends what kind of sex you are having. Anal beein more risky than vaginal and receptive beeing more risky than insertive. (pardion the generic medical terms..) For clarity I have put the most relevant numbers in bold 😉.

Receptive anal 1,38% (95%CI: 1,02"-1,86%)
Insertive anal 0,11% (95%CI: 0,04%-0,28%)
Receptive vaginal 0,08% (95%CI: 0,06%-0,11%
Insertive vaginal 0,04% (95%CI: 0,01%-0,14%)

Oral (both ways) is simply referred to as "Low"
https://pmc.ncbi.nlm.nih.gov/articles/PMC6195215/

I will respect the threads intention but will still allow myself to mention that PREP reduces the risk with an additionally 99% wich gives a residual risk for insertive anal and vaginal sex respectively at 0,0011% and 0,0004% 
https://hivinfo.nih.gov/understanding-hiv/fact-sheets/pre-exposure-prophylaxis-prep

 

Edited January 22 by navinor

[hormone]

3 hours ago, navinor said:

Thank you @hormone for doing the research!

The risk varies with viral load of the person that is HIV+, one basic rule is that if the person in well medicated an thus has zero viral load, also known as "U=U"
 https://hivinfo.nih.gov/understanding-hiv/fact-sheets/understanding-hiv-transmission

Receptive anal 1,38% (95%CI: 1,02"-1,86%)
Insertive anal 0,11% (95%CI: 0,04%-0,28%)
Receptive vaginal 0,08% (95%CI: 0,06%-0,11%
Insertive vaginal 0,04% (95%CI: 0,01%-0,14%)

Oral (both ways) is simply referred to as "Low"
https://pmc.ncbi.nlm.nih.gov/articles/PMC6195215/

I will respect the threads intention but will still allow myself to mention that PREP reduces the risk with an additionally 99% wich gives a residual risk for insertive anal and vaginal sex respectively at 0,0011% and 0,0004% 
https://hivinfo.nih.gov/understanding-hiv/fact-sheets/pre-exposure-prophylaxis-prep

 

THanks for your comment!  (again here I am copy/ pasting/ editing a post I made in a bb thread... as not everyone reads those threads lol) 

The numbers you quote @navinor come from  the work of Dre Marie-Claude Boily a world expert on epidemiology/ mathematical modeling of HIV transmission.  She & her team have tons of other papers too... This is the landmark one: 
https://pubmed.ncbi.nlm.nih.gov/19179227/ 

For people who may not know, this is how risk of HIV transmission has been calculated : 

1-Following HIV negative populations over time, counting number and types of sexual exposures & number of seroconversions obviously.  The better studies use sero-discordant couples (one HIV+, one HIV negative).  It's not exactly easy to be precise all the time (some people won't admit the truth, some won't remember who they had sex with, or how many partners, etc). And not all studies use these couples.  
The current numbers we know/use for receptive anal, receptive vaginal and insertive vaginal are from meta-analyses.  For insertive anal, it's taken from 2 individual studies that could not be pooled together for meta-analysis.  These numbers are for "high income countries".  Risk is actually higher for low income countries.  From Dre Boily's paper, they used: 
"43 publications comprising 25 different study populations were identified. Pooled female-to-male (0.04% per act [95% CI 0.01-0.14]) and male-to-female (0.08% per act [95% CI 0.06-0.11]) transmission estimates in high-income countries indicated a low risk of infection in the absence of antiretrovirals. Low-income country female-to-male (0.38% per act [95% CI 0.13-1.10]) and male-to-female (0.30% per act [95% CI 0.14-0.63]) estimates in the absence of commercial sex exposure (CSE) were higher." 

One reassuring thing about vaginal insertive 0,04% is probably correct is that this number also is very similar to risk of transmission with a needled-stick injury with HIV+ blood (actually this was the 1st ever transmission risk number to be available historically).  

2- If a given female population (or region ...) has a HIV prevalence  of 25% vs 1%, it won't affect the risk of EACH act.  But it will affect the total number of potential transmissions in this population though.  And as the act is repeated, eventually there will be more cases... 

3- Infection transmission risk has various modifier factors, from the "donor", the receiver and the type of contact itself.  Well known factors increasing risk have to do with breaks in the skin/ mucosal integrity .  As @navinor mentions, the viral load is super important.   Undetectable?  Extremely low risk.  High viral load?  It makes the HIV+ person way more infective... so the receiver is more likely to sero-convert!  If ONE HIV virus penetrates your blood stream, it does not mean you will seroconvert.  There are lots of other processes down the chain. But if more penetrate, the higher chances you will sero-convert... (which links my point about lots of HIV cases being diagnosed in late phase here in TH, so more infectious... ).  
From the same above Boily paper:  
"Estimates for the early and late phases of HIV infection were 9.2 (95% CI 4.5-18.8) and 7.3 (95% CI 4.5-11.9) times larger, respectively, than for the asymptomatic phase." 
Early and late phase HIV infections are the periods with the greater viral load in the infected person...   

[navinor]

@hormone You obvoiusly have some knowledge about this🤓

Lets make this into a real life example:

Lets say that I am about to go ballistic in Pattaya and bareback everyone i can...
I spend one week in heaven, on PREP, with 4 pops a day. 

Lets for ease of calculation assume that I am able to avoid girls in late and early stage HIV and that I only practice "insertive vaginal" sex.

This would entail; 28 instances of said practice (4*7) 
If all of those were with a girl that were HIV+ and with an average viral load that would give each instance a risk of 0,0004% of an adverse outcome (beiing infected). This will give me a cumulative risk of 0,0112% of at least one adverse outcome, and as we know - one is enough...

Simply put: I would have a 0,0112% chance of getting HIV after plain bareback vanilla sex with 28 HIV+ girls

Please correct my math if I am wrong!
Also please do not take this as a sign that unprotected sex is risk free regarding HIV, even on PREP, but as the author intended lets keep this fact based.

[Cooldehla1]

https://pmc.ncbi.nlm.nih.gov/articles/PMC4467783/pdf/nihms-391611.pdf

 

With further stratification by setting (developed versus developing countries), the heterogeneity across gender-specific study estimates was no longer significant for developed countries only. The pooled C, F-to-M and M-to-F developed country estimates were 0·0008(95%CI 0·0004-0·0016), 0·0004(0·0001-0·0014) and 0·0008(0·0006-0·0011) respectively. In contrast, the pooled F-to-M and M-to-F estimates for developing countries were 0·0087(0·0028-0·0270) and 0·0019 (0·0009-0·0043), respectively.



Because thailand is a developing country, i would say the risk factor is than not 0,004% per sexual act but somewhat higher, to 0,028%

Edited January 22 by Cooldehla1

[navinor]

I'm not sure I understand..

That is 7 times the risk. 0,004% is given the fact that your partner is already HIV+ with an average viral load.

Is the underlying assumption here that the viral load is higher in developed countries? Also, as far as I know Thailand, and in particular Pattaya has a much higher focus on HIV than other developing countries. 

Not saying you are wrong, just that I dont understand...🤔

[navinor]

Ment developing countries, not developed countries regarding viral load, sorry...