A quarter of people who leave a sexual health clinic with ‘undiagnosed HIV’ are taking HIV treatment

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In the UK, around a quarter of people thought to have had their HIV infection undiagnosed during a sexual health check-up have in fact been previously diagnosed HIV-positive and are taking antiretroviral therapy. These results, presented to the British HIV Association conference in Bournemouth yesterday, provide the first objective evidence of a widely suspected phenomenon.  

The anonymous testing of people attending sexual health clinics has revealed some puzzling findings. In this programme, blood samples from individuals testing for syphilis at a sexual health clinic are anonymised and then tested for HIV. The 2009 results show that 2.4% of gay and bisexual men and 0.25% of heterosexuals tested came to the sexual health clinic with undiagnosed HIV.

Moreover, only 63% of people with undiagnosed HIV were actually tested for HIV while at the clinic - much lower than the average testing rate for clinic attendees. Are the people most in need of an HIV test actually less likely to take it than others?



A sexually transmitted infection caused by the bacterium Treponema pallidum. Transmission can occur by direct contact with a syphilis sore during vaginal, anal, or oral sex. Sores may be found around the penis, vagina, or anus, or in the rectum, on the lips, or in the mouth, but syphilis is often asymptomatic. It can spread from an infected mother to her unborn baby.

unprotected anal intercourse (UAI)

In relation to sex, a term previously used to describe sex without condoms. However, we now know that protection from HIV can be achieved by taking PrEP or the HIV-positive partner having an undetectable viral load, without condoms being required. The term has fallen out of favour due to its ambiguity.

anonymised data

Information about a patient from which the name, address and other identifying information has been removed.


Studies aim to give information that will be applicable to a large group of people (e.g. adults with diagnosed HIV in the UK). Because it is impractical to conduct a study with such a large group, only a sub-group (a sample) takes part in a study. This isn’t a problem as long as the characteristics of the sample are similar to those of the wider group (e.g. in terms of age, gender, CD4 count and years since diagnosis).

acute infection

The very first few weeks of infection, until the body has created antibodies against the infection. During acute HIV infection, HIV is highly infectious because the virus is multiplying at a very rapid rate. The symptoms of acute HIV infection can include fever, rash, chills, headache, fatigue, nausea, diarrhoea, sore throat, night sweats, appetite loss, mouth ulcers, swollen lymph nodes, muscle and joint aches – all of them symptoms of an acute inflammation (immune reaction).

The problem could lie with a failure of clinicians to offer testing to certain people, or with a refusal by clinic attendees to take the test. This may be because individuals fear a positive result or are unconvinced of the benefits of testing.

Alternatively it has often been suggested that some of the people with ‘undiagnosed HIV’ are not undiagnosed after all. Some HIV-positive individuals may wish to keep their HIV status secret when having sexually transmitted infections diagnosed and treated. This could be due to being concerned that discussing unprotected sex with healthcare staff could provide evidence that would be used against them in the event of an accusation of criminal HIV transmission. More simply, some may wish to avoid unwanted, intrusive or stigmatising discussion of their sexual behaviour.

Although most hospitals providing HIV treatment and care also offer sexual health services, the UK’s open-access system for these services means that it is possible for individuals to seek care at more than one hospital.

The study reported yesterday provides the first clear evidence that people with diagnosed HIV are in fact attending sexual health clinics without acknowledging their HIV status. In a quarter of blood samples from people who had refused HIV testing, there were traces of antiretroviral drugs.

For this exploratory study, the Health Protection Agency gathered a convenience sample of 206 blood samples from individuals who had not been tested for HIV at a sexual health clinic (but who had given blood for a syphilis test). The samples came from a range of clinics, between 2005 and 2009.

In terms of demographic groups, 121 samples were from gay or bisexual men; 38 were from heterosexual men; and 47 from women. Four out of ten samples were from a person who had an acute sexually transmitted infection.

Overall, ARVs could be detected at therapeutic levels in 27% of the samples. In most cases, three drugs could be detected. These individuals would appear to be attending a sexual health clinic where they do not reveal their HIV-positive status. Contrary to expectations, ARV detection rates were a little lower in gay and bisexual men (24%) than in heterosexual men (32%) and women (32%).

The researchers apply these estimates to existing data:

  • Looking at gay and bisexual men accepting a syphilis test but refusing an HIV test, 9 in 100 are HIV positive. The new data suggest that at least 2 are on treatment and not disclosing their status.
  • For heterosexuals accepting a syphilis test but refusing an HIV test, 8 in 1000 are HIV positive. At least 2 are on treatment and not disclosing their status.

The overall impact of this data on estimates of undiagnosed HIV in the population is thought to be modest.

But what about people who are not aware of their real HIV status and who avoid HIV testing? What are their motivations?

 A small study presented to the conference shed some light on why gay men at risk of HIV infection refuse the offer of a test. Researchers at two clinics gave an anonymous questionnaire to 19 men who didn’t want to be tested although they had had unprotected anal intercourse since their last HIV test or had had unprotected anal intercourse without ever testing.

Fifteen of the 19 men considered themselves to be at low risk of HIV infection.

When asked why they hadn’t tested that day, 14 said they were emotionally unprepared for a positive result. In addition, several said that they disliked having blood taken (4 men), were concerned about prosecutions for HIV transmission (4), were planning to test next month (4) or had fears about the confidentiality of the result (3).

Although men were generally aware of the possible advantage of being able to access HIV treatment, they could name a number of disadvantages to testing. Almost all said testing was stressful (17 men), while others were worried about informing a boyfriend about an HIV positive result (8) and the implications for insurance and mortgages (7).


Savage EJ et al. Use of laboratory tests to study non-disclosure of HIV status within the Unlinked Anonymous Survey in GUM clinics. 17th annual British HIV Association conference, Bournemouth, 2011, Abstract O13.

Whitlock G et al. Why do men who have sex with men who are at high risk of HIV infection decline HIV testing? 17th annual British HIV Association conference, Bournemouth, 2011, Abstract P152.