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In urban emergency departments, the most common scenario for consideration of nPEP involves a patient presenting for evaluation following a high-risk sexual encounter, consensual or not. Again, the first issue is to assess the degree of risk, based on exposure characteristics (Table 55–1). In instances where one partner is known to be HIV infected, the risk of anal intercourse is higher than for vaginal intercourse. Receptive anal intercourse with an HIV-infected partner carries an estimated risk of HIV transmission of 0.3–0.5%. Vaginal intercourse carries a risk estimated at one-tenth that of anal sex (0.03–0.09%), with receptive partners more at risk than the insertive partner. Oral sex is associated with a minimal, but not zero, risk of transmission. Intercourse during menses, and traumatic intercourse, as in cases of sexual assault, carry an increased risk of transmission.
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For the pediatrician, the consideration of nPEP is generally in relation to exposures from common childhood behaviors, such as biting between children, or puncture wounds from discarded needles found on playgrounds. Although in certain conditions viable virus can be recovered from 8% of syringes and needles up to 21 days later, the risk is quite low. To date there have been no cases of documented transmission of HIV from puncture wounds from discarded needles.
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There are several cases of purported transmission of HIV through biting or other in-home exposures, but there are no well-documented cases of HIV transmission between children through biting. HIV is rarely isolated from the saliva, and there are inhibitory molecules in saliva that reduce infectivity, therefore the risk of transmitting HIV through biting is believed to be extremely low. The few cases of in-household nonsexual transmission of HIV have involved direct exposure to infected blood.
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In a pediatric hospital setting, inadvertent exposure to breast milk may occur as well, through the inadvertent offering of stored breast milk to the wrong infant. A meta-analysis of prospective cohort studies estimated the risk of transmission of HIV-1 through breast-feeding in infancy as 16%.12 The risk increases with longer duration of breast-feeding, high maternal viral load, the presence of mastitis and mixed formula and breast-feeding.13 However, the risk from a single feeding of infected breast milk is quite low, estimated to be 1–4/100,000. In addition, in the United States most women are HIV-tested during pregnancy and, if HIV-infected, strongly instructed to avoid breast-feeding. The likelihood, therefore, that a breast-feeding woman is HIV-infected, and that a one time exposure to her milk will transmit HIV, is minimal.
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In the Emergency Department, or the Pediatric office, the first step in assessing the need for nPEP is in evaluating the significance of the exposure, as the risk of transmission of HIV varies greatly based on the type of exposure (Table 55–1). The risk is highest following transfusion of HIV-infected blood, where up to 90% of recipients will convert to HIV positive status. Other common exposures carry a risk of infection ranging from 13% to 25%, for perinatal exposure in the absence of breast-feeding, to 0.01% (for receptive oral sexual encounters).