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HIV PRE-EXPOSURE PROPHYLAXIS (PREP)

HIV Pre-Exposure Prophylaxis (PrEP) is an HIV preventive treatment that uses anti-HIV medications to greatly reduce the risk of infection.

It is recommended for anyone who engages in high-risk activity – this usually includes men who have sex with men, men who have sex with commercial sex workers, and among people who inject drugs. Most of the time, PrEP is taken daily as a single pill of a combination of 2 anti-HIV medications – if taken properly, this can reduce the risk of contracting HIV through sex by more than 90%.

There are also other ways that PrEP can be taken, including as Event Based Dosing (EBD), Holiday PrEP, and with the T’s and S’s regimen.

Even while on this medicine, we will still strongly advise the patient to continue practicing safe sex and get regular HIV tests. HIV PrEP does not prevent other STDs.

Our doctor will counsel you on the suitability of PEP, potential side effects, and may need to perform a rapid HIV test (to ensure there is no previously established infection) and baseline blood tests for kidney and liver function as well. The doctor will also counsel on other STD risks, testing, and treatment or prevention as needed.

Polymerase Chain Reaction (PCR) HIV RNA/DNA TEST

The HIV PCR RNA test is used to detect HIV viral copies at the very early stage of HIV infection before antibodies have developed. It is the earliest way to detect an HIV infection and can be used accurately from 10-12 days post-exposure. The HIV PCR RNA test is also used to test for HIV Viral Load counts for people living with HIV and who are undergoing HIV treatment with Highly Active Antiretroviral Therapy (HAART). This test can be performed at all of our clinics; however, it cannot be performed anonymously. Anonymous HIV testing (AHT) can only be performed at our Robertson Walk clinic with our Rapid 3rd or 4th Generation Test kits.

HIV Pro-Viral DNA Test

The HIV Pro-Viral DNA test can be used in specific situations where there are challenges to getting an accurate HIV diagnosis with other available HIV tests including HIV Antibody tests (3rd Generation HIV test), HIV Antibody and Antigen tests (4th Generation HIV test) as well as HIV RNA PCR test.

It is especially useful in the following situations:

1. Diagnosing HIV in newborns born to HIV +ve mothers
2. Elite controllers with undetectable HIV viral load despite not being on anti-retroviral treatment
3. Individual with sero-negative HIV infections i.e. People who get infected with HIV but do not develop anti-HIV antibodies : see FALSE NEGATIVE HIV ELISA TEST

It can be used for situations where the diagnosis of HIV is challenging. It has a lower false positive rate compared to the HIV RNA PCR test when used for diagnosis and it can be done 10 days post exposure.

HIV P24 Antigen/Antibody Combo Test (4th generation)

The 4th GenerationHIV p24 Antigen/Antibody Combo Test detects HIV antigen (p24) and/or HIV antibodies.
The HIV p24 antigen is a protein that makes up much of the HIV viral core and can become detectable from 12-20 days post-exposure, usually reaching a peak at around 3-4 weeks, and dropping to lower levels after 5-6 weeks once HIV IgM antibodies start forming. Although this p24 antigen can usually be detectable by 14 days post-exposure, there will be a number of people who may not have detectable levels until later (up to 28 days post-exposure). This is why we say this test is most accurate after a 28 day window period.

Once HIV Antibodies start to form, the p24 antigen levels will drop and become undetectable again – this process is known as seroconversion. Very few people will have a delayed seroconversion, where p24 antigen levels do not drop because antibodies are not being formed – however, as the 4th Generation Combo test will test for both p24 antigen and HIV antibodies, it is adequate in detecting an infection any time from 28 days post-exposure onwards.

This test can be performed anonymously at our Robertson Walk clinic only. – HIV Screening Singapore / HIV Clinic / HIV Test Clinic Singapore

HIV Antibody-only Test (3rd generation)

The 3rd Generation HIV Antibody-only Test will only detect for HIV antibodies in the blood or saliva. HIV antibodies can become detectable from about 14-20 days post-exposure. However, this process may take longer in some people.

By 3 months post-exposure, over 99.9% of people infected with HIV will have detectable antibodies. For those who do not have detectable antibodies (delayed seroconversion), a 4th Generation HIV p24 Antigen/Antibody Combo test will be able to detect the virus. – HIV Screening Singapore

Different studies show different HIV Transmission Risk.

Below is a summary based on US CDC MMWR, UK guideline for the use of PEP (UK PEP), Alberta guideline for the use of  PEP (Alberta PEP), Australian Society for HIV Medicines (ASHM) and New York State Department of Health AIDS Institute (New York).

As expected there are large discrepancies in the estimated risks. Receptive anal intercourse is invariably the highest risk sex act.

1. Condoms – There have been many studies on the effectiveness of condoms in reducing HIV risk. Results range from 60% to 90%. The US CDC Condom Report published in 2001 estimated the average protection rate to be 87%. Condom use should therefore be encouraged for all patients.
2. Treatment as Prevention – People living with HIV on AntiRetroviral Therapy (ART) are about 90% less likely to transmit HIV. This could be due to the decreased viral load.
3. Circumcision – Circumcision has been found to reduce the risk of contracting HIV by about 60%. This may be due to the removal of the foreskin which is rich in Langerhan Cells.
4. Other Factors:

(Reproduced from the Sanford Guide to HIV/AIDS and Hepatitis Therapy 2014)

The chances of HIV risk will increase when you or your partner are infected with other Sexually Transmitted Diseases