Dr. Tan and Partners is one of the few approved Anonymous HIV Testing Centres in Singapore. A detailed write up on our service is available here.

Other STD services: Early STD Screening, Rapid Hepatitis B Blood Test, Swab for Gonorrhea and many more... contact us to make an appointment now!

All about HIV Types, Subtypes, Groups and Strains

180px-HIV-SIV-phylogenetic-tree.svgI often get questions from people worried about having some ‘strange strain’ of HIV that cannot be picked up by tests.

Let’s take a step back and try to understand all this rather confusing terms of Types, Subtypes, Groups and Strains of HIV and see if it can shed any light on such concerns.

Scientist love to categorize things into neat little boxes. This is no different for living things. The science of taxonomy is an interesting one. Lets starts with viruses. We all know what viruses are. There are many different Families of viruses. What we are interested in is the Family Retroviridae. In this family, we further sub classify into Sub-Families like Orthoretroviridae. Which we then sub classify into Genus like Lentivirus and again into Species like the Primate Lentivirus Group. Into this neat little box that we have made, lies the HIV virus. i.e. HIV = Family Retroviridae, Sub-Family Orthoretroviridae, Genus Lentivirus, Species Primate Lentivirus Group. The Simian Immunodeficiency Virus also fits into this box but this is just trivia.

There are 2 Types of HIV, Type 1 and 2. They are similar in many ways except for geographical distribution, ease of transmission and speed of disease progression. HIV type 1 is further classified into Groups (M, N, O, P) and subtypes (A, B, C, D, F, G, H, J, K, CRFs). CRF is an acronym that stands for Circulating Recombinant Forms. They are basically products of different HIV subtypes combining together. HIV is classified as such according to their genetic makeup.

So aside from an overwhelming level of complexity that gives scientists a really big kick; what exactly is the use of classifying HIV down to such a degree? The real difference it makes is in people who live with the HIV virus. Knowing exactly the type, group and subtype of HIV we are dealing with makes a big difference in treatment and monitoring.

But what does it mean for people who do not have HIV? Or who have been exposed to HIV and are testing for it? The fact is types, groups and subtypes of HIV are rather geographically distinct. Knowing which predominates in a particular area will help policy makers decide on the appropriate HIV screening tools. Thankfully, most modern tests are able to pick up all forms of HIV. Our clinic uses the Determine and Oraquick rapid tests which are able to test for both HIV Type 1 and 2 and even the dreaded Type 1 O Group.

Although it looks all neat and nice now, the fact remains that science is an ever changing field. No doubt there will be more discoveries of new subtypes and CRFs. We can only hope that testing technology will be able to keep up.

All Our Doctors are Fully Certified and Trained to conduct specialised HIV Testing.

Your are welcome to visit Our Doctors at Our Clinics anytime during our opening hours.

Click Here for Contact Details, Address and Opening Times.
Click here to contact us

Our Andrology and Infection Centre at Novena Medical Center is open.

Call us at 63972095 now to book your treatment.

More on HIV symptoms.

If you have any questions, visit our free online forum on sexual health, HIV and STDs.

If you need a HIV test visit Our Clinics anytime during our opening hours. You do not need an appointment.

Find out more about Anonymous HIV testing at our clinics.

Can’t wait for 3 months to find out? Find out more about Anonymous Rapid HIV Combo test at our clinics.

If you had a high risk exposure to HIV within the past 72 hours, you can take medicines to reduce your risk of actually contracting HIV. Find out more on HIV PEP Treatment.


Need more advice?

Come down to Our Clinics for a discussion with Our Doctors, or call our clinics for more information:

Singapore Branches


Where to find us – here

Selected clinics are open on Saturday and Sunday.

Email: hello@dtapclinic.com.sg

All Our Doctors are Fully Certified and Trained to conduct specialised STD Screening,  STD Testing & STD Treatment and HIV Testing.

For lady patients who prefer female doctors, we have professional certified female Doctors to attend to your medical needs.


About Dr. Tan
Dr. Tan graduated from the National University of Singapore in 2001. His residency was in the two largest public hospitals in Singapore; Tan Tock Seng Hospital and Singapore General Hospital.

Find the profiles of our panel of doctors.


  1. Would a duo test (by roche) pick up HIV type 2 by five weeks (35 days)?

  2. Good afternoon Dr Tan & partners,

    I have got this serious anxiety the last 2 years. In mid Oct 2015 (around 13/14 Oct) I had an unprotected sexual intercourse with a female in my mess. She’s a new acquainted.

    It was just once. After that I was infected by gonorrhea. I got a treatment from a genital specialist around 3 days after that & I healed.

    After that my body was still unwell. I felt weak, fatigue, got joint paint, headache, flu.

    In 27 Nov 2015 I rechecked to a genital specialist again (different from the first one). He referred me to do a lab checkup with regard to the genital disease.

    The results were:
    Anti HIV : non-reactive – ELFA method
    Anti HSV : non-reactive – EIA method
    VDRL THPA : non-reactive – Chromat ographic Immuno assay method
    HSBAG : non-reactive – CMIA method
    Anti HCV : reactive – CMIA method

    Based on the conclusion of Hepatitis C positive, I checked to liver specialist, & got a treatment of Sofosbuvir & Ribavirin for 6 months since February 2016 – September 2016. During the treatment I got more fatigue, digestion problem, headache, lost weight.

    After the treatment ended, I need to check the Hepatitis C quantitative every 3 months, and thanks God the virus consistently undetected until now.

    The problem is, my body still feel unwell. Headache has pretty much subsided. But fatigue & gastro issue still remain. Unlike other gasto issues, my defecate does not discharge like 5 – 10x a day. But my stomach is still unwell, sometimes pain. Sometimes my pop is dense, sometimes it is not.

    And. In 6 June 2017 I checked my CD4 & CD 8. The results were:
    CD4 : 1110
    CD4 % : 37%
    CD8 : 870
    CD8 % : 29%

    And last week (28 Sept 2017), I rechecked again. And the results were:
    CD4 : 965
    CD4 % : 38%
    CD8 : 751
    CD8 % : 30%

    What are those conditions above telling me roughly? Am I infected by HIV? Was the Anti HIV ELFA result on 27 Nov 2015 actually a false negative, as it was just approximately 43 – 44 days (1.5 months) since the last exposure. I heard that the HIV test is supposedly conducted at least 3 months after the last exposure. But I’m scared.

    Or is my unwell condition due to the long-term effect of Hepatitis C medication? Or is it another symptoms of disease?

    After that test I did check the VDRL TPHA, HBSAG, Anti HSV in December 2016 (1 year after the last checkup). And all negative. But never check the HIV again. I’m very scared if it turns out the last result was false negative & actually positive. I only check the CD4 & CD8, & they showed some decrease within almost 4 months.

    Please kindly expecting your feedback & info. Thank you.

    • I see no reason to doubt the accuracy of your HIV test, but if you have concerns, just repeat the test. There is no harm in that. You should have this discussion with your ID specialist, especially with regards to your medications and symptoms. If you wish to visit us for a consult and evaluation, we would be happy to discuss your tests in person.

      • Thanks for the response, Dr Jonathan.

        What about the common rule that the window period is supposedly at least 3 months, and therefore, checking before that period of time will not conclude anything?

        Moreover, I read your article below that if someone is infected with HCV, then the window period for HIV will be up to 12 months. And I used to be infected (although it’s already clear now).


        Those info above are affirmed with the unwell symptoms I feel the last 2 years.

        Please kindly expecting your feedback on this matter.

        Regarding your invitation to visit your clinic, unfortunately I’m not residing in Singapore. But will do visit once I travel there. Thank you.

  3. Hello doctor, I read your posts and I wanted to ask your opinion on my risk. On 07/16/16 I had a sexual encounter with a male (I’m a female) and I was on me menses, the sex was unprotected. We both have had a few drinks. 3 weeks past that I come down Ill with fever, recurrences of cold sores which I’ve gotten only on in my life, and this time they kept on coming and coming. I developed gastro problems as well, dry mouth, I had fever for 1 1/2 week.. then the fever would come and go. I also had one swollen lymph nose along with vaginal yeast infection. My tongue got white and I now developed muscle twitches everywhere. I’m very concerned. I tested for HIV 1/2 at 4,5,7, 10 and 13 weeks post exposure and it came back negative. I now have the twitches and gastro issues still. I developed some form of cervicitis which I’m on antibiotics right now. My doctor said I should wait for 6 months.. I can’t wait that long. Are my tests reliable? The guy travels a lot and I’m afraid I caught some weird strain of HIV.

    • I do not know exactly what tests you did. There are many different types and brands of HIV tests all with their own degrees of sensitivity. So I am unable to comment on the accuracy of your test. Since your doctor said you need to retest at 6 months, you had best heed his/her advice.

  4. Hi dr.tan
    My qusion is can the Elisa test detected all crfs of hiv1 or a few of them?


  5. Anxious

    Hi Dr,i been taking a NAT test one month post exposure and the result is Non Reactive, should i get another Combo test? or i can conclude that i am HIV free??

    • Honestly that is an unfair question to ask us. In order to answer that we have to make way too many assumptions. That question really should be directed at the doctor who did the NAT test for you. Hey, you paid him for the consult. You should get your questions answered.

  6. I mean to say will your hiv tests still pick up group p and group n virus because of cross reactivity.or will it not pick up group p and group n in any means.

  7. Will there be cross reactivity of your hiv test with hiv group n and group p.Will they possibly pick it up.or will it be silent negative.

  8. Does determine oraquick and combo hiv test detect hiv group n and hiv group p

  9. Dr tan plz reply does your determine rapid hiv test and oraquick rapid hiv test detect hiv O group virus.

    • According to the official product insert of the Determine HIV Antibody Rapid test kit, the sensitivity of the test kit to HIV-1 Group O tested across 12 specimens was 100%.

  10. Does a 3 rd generation antibody test identify crf ae

  11. There is no exposure for at least 1 year . Hiv I and II ( ELISA ) the result is 0.72 which is no reactive which is done by cmia method. Further detection of hiv p24 antigen and hiv I and II antibodies by card method ( no band) and by elfa method 0.02 both of which are negative but by cmia method the reading is 1.33 ( reactive ). Does it mean I am infected by hiv and wot does it mean.
    ELISA test is done after card method and elfa test and cmia method for detection of p24 antigen and hiv I and II cake positive with 1.33.

    • I do not quire understand your question. Are you saying you have CMIA +ve, ELISA -ve, ELFA -ve? If so then by definition you do not have HIV. See your doctor for more advice.

  12. hello I am having HIV subtype E which is not prevalent in India. four people injected drug when I was in Thailand and took away my money. I was under depression from last 7 years.

    In India all test comes negative HIV 1 & HIV 2 as well. I came to know that kits available in India cant detect hiv subtype E. I am having CD4 count 500 now and want to start ART treatment. cd4/cd8 ratio is 0.80 less than 1, but dr here are saying you do not have HIV`pls help
    Western blot test for HIV 2shows indeterminate results and showing weak positive results for p26.
    I am having burning sensation in legs and arms. oral thrush like symptoms. sometimes I get burning sensation in thighs and genital area. what other STD can give me such symptoms. Vitamin B12 test done all tests are normal. there is increase in Gamma Globulin 1.33 gm%.in Serum Protein Electrophoresis.

  13. Samir Hussain



  14. Samir Hussain

    HIV SCREENING : HIV BY CARD : NO BAND,CMIA :2.57,,4.94,5.93,5.39,5.29,5.87(<1.00) ELFA : 0.02,0.03,0.04,0.02,0.05,0.04,0.02,0.03(<0.25),W.BLOT FOR HIV1 & 2 NEGATIVE FIRST MONTH.NOT DONE HIV QUALITATIVE PCR.PLEASE SUGGEST.


  15. Madison

    Hello Dr. Tan,

    I had a rapid finger prick test and oraquick oral fluid test done a few weeks ago, and my last sexual exposure was 4 years ago. The result was negative. Can the rapid finger prick tests pick up CRFs?

    Thank you for everything

    • CRFs will also induce an antibody response. Modern HIV tests detect the presence of antibodies which indicate a HIV infection regardless of the strain. Please post follow up questions on http://www.askdrtan.com

  16. Hey Dr.tan i just wanted to ask that i recently donated blood to an organization which is registered i guess because they have web page etc. what i wanted to ask was that the aluminium bag from which the guy took out the blood bag was already opened but he did take the cap off from the insertion needle it’s been two weeks i don’t have any symptoms but i am a mode of hyper tension that i might have HIV i called the institution and they said that the blood bags cannot be reused and they cut every needle from after it is used. but some how the tension is not going away. can you please tell me that is it possible for me to have been infected??

  17. Hi please help! I had unprotected receptive anal sex with another male 2 months ago plus, I’ve had tests done at 2 and 6 weeks and the guy I slept with also took at test at 6 weeks, all negative thank god. however still anxious and finding twos situation difficult. I’ve spoken to doctors yet am still curious whether I should look at my 6 week test as conclusive and his test? I had no symptoms (cough,fever etc) but I did have blocked noise and mild sore throat (very mild) I question if it was only in my mind from worrying. anyways I was curious about what you think? thank you it would be a massive relief.

    • It depends on what tests you did. However, most tests would be very indicative at 6 weeks if not conclusive. However, most health authorities still recommend a retest at 3 months. Please post any follow up questions on http://www.askdrtan.com

  18. Dear Dr.Tan ,

    Thanks for the insight . I am an Indian 4 years back I received oral sex from a prostitute in central europe. Since 2 years I am not well .Diarrhea , sweating , skin rashes,running nose ,tiredness and weakness are the few symptoms . I got tested in india with 2 antibody tests ( MEIA, chemiluminescence , 2 rapid , dna pcr , Nat test ,2 westernblots. All negetive. I am still worried as i m not well and think that i m infected by some unusuaal strain or subtype prevelent there which the tests in india are not able to pick.Please suggest ?

    • I do not know of any mysterious subtypes that cannot be picked up by modern HIV tests. If this truly exists and cannot be detected by any tests, then I would not know of it either until some heroic scientist somewhere discovers it.

  19. Hey Dr. Tan I had unprotected sex three years ago and just this past week I took the uni gold test which turned out to be negative but I still have these fears in my head mostly because I have all the symptoms I get cold sores now which I use to never get only when I was a child I’m now 22 and have had 3 this past year , abnomial pains, fatigue…. My main question is does the unigold pick up all strains I live in atlanta ga i know there are alot of strains out there mostly in other countries. I’m just worried because the girl I had unprotected sex with could have been exposed to one of these foreign strains. Also I did have flu like symptoms 2 months after I had sex with this girl ( coughing, chills night sweats) and I never get sick this was actually the last time I’ve been sick.

    • I am not took familiar with the Uni Gold test. Since your concern is the test not being able to pick up all HIV subtypes, I suggest you see a doctor and get a standard ELISA test done. You wouldn’t have the same concerns with the ELISA test. I put much more credence on test results than I do symptoms.

  20. Hi Doctor,

    Nice article. I did an HIV MEIA test 4th generation in the middle east at 12 and 13 weeks after an unprotected fellatio and protected vaginal intercourse. I know it is a low risk. However I would like to know if these tests will detect for sure any group/subtype of HIV and if not would a RNA test be more accurate.

    By was of clarification if there is a new group/subtype would a modern test still detect the HIV virus?

    Thank you very much.

    • I am not aware of any new groups or subtypes that cannot be detected by current tests.

  21. Is there a HIV test, two different people can have done to determine if one person infected the other?

    • Yes. You can take the HIV virus from the 2 individuals and look for unique genetic features. They will not be identical but they can be close enough for us to be reaonsably statistically confident that one of these individuals infected the other.

  22. Dear Dr. Tan,

    I had protected Sex with a working girl about 10 days ago. However, my condom broke and I might have had unprotected sex for abou 3-4 minutes. I could get my penis out before I had an organsm. After I have realized what has happened I was scared as hell and went to the local hospital and started PEP (about 4 hours after) with a local genereica (Zilvarir).
    My questions are: Do have cheap genereica the same effect as original medicines? Does PEP help against Subtype E? The girl has only been working as a prostitute for 3 weeks. I am very scared.

    • I am not aware of any studies on the PEP regime you are on so am unable to comment on its efficacy. PEP works against all subtypes. Please post any follow up questions on http://www.askdrtan.com

  23. Jamie Hazlewood

    Dear Dr Tan

    I would just like to say thank you for your great work and good advice you give here on your website.

    I am in a similar situation to someone who has already posted.

    I recently visited Thailand and had unprotected vaginal sex with a Thai girl I met at a bar. I texted her after with my concerns and she reassured me she wasn’t a typical bar girl and that she regularly got her blood checked so would be clear of any infections. Obviously I don’t know if I can trust this information, I mean why would she get her blood checked regularly anyway?

    Today I had a rapid HIV test (finger prick) and it came back negative. It is exactly 25 days since my possible exposure with HIV. I have been advised to go back in 3 weeks for a conclusive test.

    So I just really wanted to get your opinion and what you think the likelihood is of me having HIV?

    Many thanks

    J H

    • Hi Jamie,

      Totally agree with your conclusions on the girl. Assuming that she was HIV +ve your transmission risk is 1 in 1000 to 1 in 10,000. Acurracy of HIV test at 25 days depends on what type of test was done. Either way, easily more than 90% accurate. I think your chances of NOT having HIV are really good. Please post any folllow up questions on http://www.askdrtan.com


      Dr Tan

  24. Dear Doctor Tan,

    I appreciate your efforts and I’d like to ask you a question please. What methods scientists use to discover new types since the HIV antibody/antigen tests seem to be unable to do that? I’m sorry but it seems to be a bit confusing, because you said there’s no doubt that there will be more discoveries of new subtypes and CRFs and we can only hope that testing technology will be able to keep up.

    Thanks in advance.

    • Hi Ginar,

      Current tests are designed to target antigens that are common to all HIV viruses regardless of subtypes, groups or strains. Current research is more aimed at improving sensitivity and specificity and reducing the window period.


      Dr Tan

  25. Dear Dr Tan
    Thank you so much. you have already answer me.π_π
    GOD bless you.

    I Did’t know how to post to your new forum .
    My mom had blood transfusion on 16 December 2011,She wants plan does HIV antibody test.Last month She also had receiving Gadarsil injection on 21may 2012..my question is Does Gadarsil injection affect the accuracy of test?She will goes
    for test on monday next week 18 june 2012.
    Thank you i am waiting your reply.

  27. Ranjan

    Dear Doctor,

    Came across your website while searching for news on HIV. I would like to your view on my case. i was detected =ve in october 2008. My. VL was 6271 and CD-4 175. I was immediately put on Virady (Atripila). Within 20 days my VL was < 50 but CD_4 never was going up. In fact it had gone down to 134. Thereafter in 2009 I tried some vague medicine (alternative theraphy) and VL was <20 and CD-4 jumped to 396. All along I ws on Viraday. Then in Feb 2011 I stopped the Viraday and tied some herbal tablets. After 45 days my VL was <20 and CD-4 was 515. I felt great and had even put on weight and was generally energetic. After 6 months however my VL was 9300 and CD-4 dropped to 298. So I resumed Virady and VL is <20 and CD-4 has crawled back to about 400. All along since 2008 I have had no symptoms. Is there is any stem cell theraphy which can hold the virus at bay without the daily medication. The daily medication causes depression to no end.

    My age is 51 and weight 74 kg and height 5'-11" and i am from India.

    Thanks for your advise

  28. Martin Chris

    Dear Doctor Tan,

    Your web site is fantastic. Thank you for your great work.

    I hope you can reassure my mind. I read on the net that Thailand has a new subtype E HIV stran that is more contagious and is easier to catch.

    I did something foolish. I was drunk, i massaged with oil and then I gave oral sex to a female Thai bar girl, and I fingered her. I do remember swallowing some of that oil after licking her vegina.

    Post exposure I was tested in Melbourne, Australia post 6 weeks. My test was negative, and the STD clinic here said that this was conclusive, and no other test is required. Since then, I have had major anxiety, have stressed severely. I have had all the usual HIV symptoms, sweats, sore throat, tired, body and muscle aches, glands hurting, fatigue, etc… This has gone on from the beginning (9 weeks now)…. I am worried that the HIV Elisa test did not pick up this Thai subtype E stran, and I might have it.

    The Melbourne STD clinic said that the 6 weeks Elisa test is conclusive, and I did not have to come back, plus they do not know anything about some new subtype stran in Thailand, even though i found this info all over the net….. info says that it is easier to catch, and harder to test for!

    I am worried sick…. The clinic in Melbourne say that they use the best testing in the world…

    Also… 6 week Syphalis, Hap A,B,C, HIV 1,2 all negative.

    What risk did giving oral sex to a lady have, if she was HIV +?
    Also…. Do you know anything about a Thai subtype E stran?

    Should I get tested again…. Please advice… Worried sick!

    • Hi Martin Chris,

      First of all, the chance of you catching HIV from your exposure is next to zero. Secondly, I completely agree with your doctors in Melbourne that the HIV test at 6 weeks is conclusive. Australia is so good at controlling HIV that Singapore sends delegations over to learn from them. So you really should place a whole lot more weight on what your Australian doctors say compared to what I say. A little knowledge is a dangerous thing. It is very easy to spread paranoia by talking about some new super bug that is completely undetectable and goes around killing everyone. There are at least 10 Hollywood movies on that theme. So instead of getting caught up in the latest end-of-the-world-superbug-scare, I suggest you place more faith in your doctors, listen to what they have to say and trust in their professionalism.


      Dr Tan