Dr Shay Keating has sent us this in-depth view of HIV risk and transmission, and the PEP treatment which can stop the infection after it enters the body
There is a risk of HIV transmission if a HIV negative person comes into contact with the blood, semen or vaginal fluids of a HIV positive person, the source.
Such transmission may occur following a needle stick injury, or exposure to damaged skin or mucous membranes (lining of the mouth or genitals), unprotected sexual intercourse, sharing needles or equipment during illicit intravenous drug use, or rarely nowadays in the developed world, by transfusion of HIV-infected blood or blood products.
Factors which reflect the probability that infection will occur following exposure to HIV are:
- the amount of the virus in the fluid (viral load)
- the infectiousness of the source, and
- the susceptibility of the person exposed.
Contact with bodily fluid with a high viral load would carry a higher risk of infection than fluid from someone on appropriate anti HIV treatment, antiretroviral therapy (ART) whose viral load is ‘undetectable’. Similarly the risk of infection is higher if the mucosa of the mouth, penis, rectum or vagina is damaged or not intact, as might occur with infections such as chlamydia or gonorrhoea, mouth or genital ulcer disease such as syphilis or herpes, and trauma following sexual assault, first intercourse or during menstruation.
Estimates have been made for the risk of HIV transmission following exposure to bodily fluids. The risk of an individual acquiring HIV following an exposure is dependant on the riskiness of the exposure, and the risk that the source is HIV positive, where unknown. The HIV transmission rate varies according to risk of exposure. Unprotected receptive anal intercourse is high, whereas oral sex without ejaculation may be considered lower risk. The risk of transmission following needle sharing in illicit drug use is high.
The risk that a person is HIV positive will vary from group to group. It is higher in men who have sex with men, and in persons from areas in the world with a higher rate of HIV infection, such as Sub-Saharan Africa. It will also be higher in intravenous drug users.
Post Exposure Prophylaxis (PEP) is a course of anti-HIV medication, given to stop a person becoming infected with HIV after the virus has entered the body. The drugs used in the PEP regime are the same as those used in ART, in the treatment of HIV infection, but for a defined period – 4 weeks.
PEP has only been used for sexual exposure since guidelines were issued in 2004. It would certainly be recommended following unprotected receptive and insertive (active) anal sex and receptive (passive) when the source is known to be HIV positive. Where the status of the source is unknown, a decision to start the exposed individual on PEP would be strongly considered by the treating physician. The PEP might be stopped if the source patient turns out to be HIV negative.
PEP is usually initiated in accident and emergency departments if STI/Infectious Diseases service are closed. It may rarely be available in some specialist GP settings, out of hours. Ideally, where possible, the HIV status of the source individual should be ascertained. The PEP is given as soon as possible, and would not be indicated or offered more than 72 hours following the exposure. Research has show that the effectiveness of PEP has greatly diminished after this time. The exposed person should be reviewed as soon as possible by a Genitourinary Medicine physician or Infectious Diseases physician, who would advise whether the PEP should be continued or stopped.
Starter packs contain 3-5 days medication. The regime can be continued, discontinued or modified at specialist review, should further information of the source blood medication history or patient’s tolerance of the medication come to light.
Side effects include nausea and diarrhoea, which can be managed symptomatically. PEP should be continued for four weeks.
PEP is not a substitute for safer sex. Studies from the UK would suggest that PEP is not regarded as a ‘morning after pill’. It would not be prescribed to those who continuously practice unsafe sex, and keep getting into situations where PEP might be indicated.
Dr Keating also reminds us that if you feel you may have been exposed to HIV, it is important not to panic. Remember there is treatment available (See Sidebar for details of Dr. Keating’s surgery at Harold’s Cross, Dublin 6w – tel. 01-4970022, Mobile: 0872345551).