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.
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?
For occupational exposure A healthcare worker will usually receive a combination of AZT (retrovir) 200mg eight- hourly or 300mg 12-hourly and 3TC (lamivudine) 100mg 12-hourly for 28 days after an HIV exposure. In some circumstances, a third drug such as indinavir is added to this treatment. A person who has had occupational exposure to HIV should be managed by experienced health personnel.
For HIV exposure through rape
A person who has been raped should receive a minimum of AZT (retrovir) 200mg eight- hourly or 300mg 12-hourly for 28 days as HIV PEP. At some centres, additional drugs such as 3TC (lamivudine) may be used. A person who has been raped should also receive antibiotics for PEP against other STDs such as syphilis and gonorrhoea. A person who has been raped should be treated by a health care professional who is experienced in the medical and medico-legal aspects of rape.
For more information on what to do if you are raped, go to http://www.speakout.org.za/
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. Most experts agree that PEP should still be given up to 72 hours after an exposure, but beyond this time it is probably 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.
A non-medical person who believes they may have been exposed to HIV through an accident or work-related injury should request treatment at the casualty department of a large hospital.
In South Africa, the Department of Health has recently agreed that HIV PEP should be given to people who have been raped. This means that all hospitals and clinics should have antiretroviral drugs available for this purpose. In practice this may not be the case, so a person who has been raped may need to seek help at a rape centre or at a large hospital in order to obtain PEP.
Antiretroviral drugs for PEP are available in private healthcare through some pharmacies. These drugs require a prescription from a doctor.
Does HIV PEP work?
The evidence that PEP works comes from one important analysis of hundreds of needlestick exposures and the relatively small numbers of HIV infections that occurred in health care workers through these exposures. Although 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 very probable infection, such as when people have accidentally received blood transfusions with blood from an HIV infected person.
It is very 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 in order to answer the question about how well PEP works after rape.
Written by Dr Jane Yeats MBChB, BSc(Med)(Hons)Biochem, FCPath (SA)Virol Specialist and lecturer, Department of Virology, University of Cape Town and Groote Schuur Hospital.