Post-Exposure Prophylaxis

Post-exposure prophylaxis (PEP) is a treatment administered to an individual to prevent the development of infection or reduce the severity of illness after a potential or documented exposure to a microorganism. This may primarily be for the protection of the exposed individual concern, or in the case of a pregnant woman, for protecting the foetus in utero. PEP may also be useful in public health to reduce the risk of secondary spread of infection. A good history is required in order to make a proper assessment of the risk. The following questions should be asked: A. Which infection is suspected and is the source infectious? It is straight forward if the diagnosis of the source of exposure is already known, e.g. known HIV, established diagnosis of tuberculosis. However, in many cases, the diagnosis of the source may not be certain, e.g. needle stick injury involving a needle of unknown origin, bitten by a stray dog, exposed to a child with a non-specific rash. In such cases, a risk assessment is required to assess the likelihood that the source may be infectious. Knowledge of local epidemiology or recent outbreaks in a particular locality may help in such risk assessment. B. What is the nature of the exposure? Knowledge of the mode of transmission of a microorganism is important to establish if there is any risk of transmission through the exposure In the case of mother-to-child transmission, PEP to the neonate born to a mother with an infection is effective if the mode of transmission is predominately perinatal, e.g. hepatitis B. If the mode of transmission is transplacental, it is too late to administer PEP to the baby after delivery. Instead, the expected mother should be given prophylaxis during pregnancy to prevent infection, e.g. chicken pox, or given antivirals to reduce infectivity, e.g. maternal hepatitis B with a high viral load when transplacental infection may occur. In HIV, where transmission can occur both transplacentally and perinatally, antiretroviral therapy (ART) needs to be given during pregnancy and often during labour as well as to the baby after birth.