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If you suspect you may have been exposed to HIV, an HIV test will confirm or deny this. The test is designed to detect antibodies to HIV, however, they will not reflect in your blood for between two and six weeks after you have been infected.

This is one of the reasons pre-test counselling is so important so you fully understand the implications of the test and the fact that you may need to retake it.

In Australia post exposure prophylaxis (known as PEP) is accessible to anyone who has been exposed to HIV. This is a treatment with HIV drugs which has been known to prevent HIV becoming established in the body, provided it is started within 72 hours of exposure.

What is post-exposure prophylaxis?
Post-exposure prophylaxis or PEP is taking action to prevent an infection after a person has already been exposed to that infection. In the case of exposure to HIV, PEP involves a course of treatment with antiretroviral drugs.

HIV PEP is usually used when there has been accidental or involuntary exposure to HIV in a medical worker, such as a “needlestick injury” or blood splash in the eye. Non-medical people may similarly be exposed to HIV at accident sites or in work-related injuries.

HIV PEP is also used when a person has had an involuntary sexual exposure to HIV such as through rape. Sometimes PEP is requested when a person has had other kinds of risky sexual exposure, such as unprotected intercourse with a sex worker or a “one-night-stand”.

HIV exposure in the work place (occupational exposure)
Medical workers can accidentally injure themselves with a needle that has been used to take a blood sample from an HIV infected person or to give an HIV infected person an injection or drip. This is called a “needlestick injury”.

Injuries with this kind of “hollow bore” needle are the highest risk category for HIV exposure because there is potentially more blood transfer than when an injury occurs with a solid sharp object such as a scalpel blade. Overall the chance of contracting HIV through a needlestick injury is about 1 in 300. A splash of blood to the eye or mouth, or blood contact with a cut or abrasion of the skin is in the lowest risk category.

Sometimes non-medical people put themselves at similar risk to medical personnel, for example assisting at an accident. If the HIV status of the source patient is positive or unknown, then PEP should be started as soon as possible.

HIV exposure through rape
There is no doubt that HIV infection occurs through sexual contact and through rape. It is not known exactly what the chances are of a man or woman contracting HIV when he or she is raped by an HIV infected person. But it is a reasonable assumption that the risk is greater than when a person engages in voluntary sex because of the trauma to the genitalia during rape.

Forced sex frequently involves microscopic and even visible tearing of the vagina or anus, which gives the virus easier access to the tissues or bloodstream. If the HIV status of the rapist is positive or unknown, then PEP should be started as soon as possible.

Which antiretrovirals are used for HIV PEP?
The adverse effects caused by some antiretrovirals and the subsequent effect this may have on whether someone continues using them remains a concern with experts. This is why, before anyone receives PEP, they must be informed of all the potential adverse effects of treatment and possible drug interactions.

The choice of which drugs are prescribed to someone is determined by considering antiretroviral treatment history, viral load and resistance patterns of the source case and the medical history of the exposed individual.

Generally, a 28-day course of antiretrovirals is recommended and, while PEP must be administered, HIV antibody testing is conducted when the infection is first suspected, and then again at four to six weeks and three months after exposure.

In Australia experts maintain there is “no direct evidence” to support the greater or lesser efficacy of three over two drug preventive regimens.

The two-drug regimens include either:
• Two nucleoside reverse transcriptase inhibitors (NRTI); or
• An NRTI plus a nucleotide reverse transcriptase inhibitor (NtRTI).

The three-drug regimens include either:
• Two NRTIs plus an NtRTI; or
• Two NRTIs (may include an NtRTI) plus a protease inhibitor (PI).

For HIV exposure in occupational setting:
In an occupational setting PEP is usually only prescribed for those who have definitely been exposed to HIV.

If the source of the suspected infection is unable to be identified or tested, then the risk of the source being HIV positive must be assessed from any epidemiological or other information available. If the source of infection is unknown the decision to administer PEP should be decided on a case-by-case basis.

For HIV exposure through rape:
Each complaint of sexual assault needs to be considered individually as soon as possible after the event.

In Australia the general rule is that male-to-male sexual assault should always receive PEP.

How soon after exposure must PEP be taken?
There is no definite answer to the question of how soon PEP needs to be taken in order to be effective. What is certain is that the sooner PEP is taken the better, “soon” being within two hours of an exposure.

In Australia the guidelines suggest that PEP should still be given up to 72 hours after an exposure, but beyond this time it is not of benefit.

Where to get PEP
Medical and paramedical personnel who have occupational exposure are usually able to obtain PEP through the medical service where they work. All hospitals and clinics should have antiretroviral drugs available for this purpose. If this is not the case, a person who has had occupational exposure should be referred to the staff health facility at a large hospital.

An HIV antibody test is available at any General Medical Practice (GP) or sexual health centre in Australia.

Does HIV PEP work?
The evidence that PEP works comes from one important analysis of hundreds of needlestick exposures and the small numbers of HIV infections that occurred in health care workers through these exposures.

Though it is difficult to analyse data that is collected by looking back at these incidents and gathering information about the circumstances, sometimes months or years after the event, the conclusion of the analysis was that PEP reduced the risk of HIV infection by 79%. Put another way, this means that a person who has a needlestick exposure and does not take PEP has a five times greater chance of contracting HIV than someone who does take PEP.

Other evidence that PEP works comes from studies in which PEP successfully reduced transmission of HIV to newborn babies delivered to HIV infected mothers. There are other situations where PEP has prevented most probable infection, such as when people have accidentally received blood transfusions with blood from an HIV infected person.

It is difficult to obtain data on whether PEP is effective for HIV exposure through rape because it is not ethical to perform a “controlled study” about this question. All the evidence points to the fact that HIV PEP will be effective, so researchers cannot deprive some people of PEP while treating others to answer the question about how well PEP works after rape.
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