HIV transmission: guidelines for assessing risk - Canadian AIDS ...

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HIV TRANSMISSION: Guidelines for Assessing RiskEVIDENCEPOTENTIALNONo RiskNOYES (under certaincircumstances)YES Negligible Risk Low Risk High RiskYES5. There must be a sufficient level of virusdelivered to establish infection.Because of a higher concentration or quantity of virus, somebody fluids are efficient media for transmitting HCV, whileothers are not. Blood is of most concern in HCV transmission.Factors Used to Determine the Levelof RiskA. Potential for TransmissionIn assessing potential for transmission, we consider the 5conditions for transmission. Because it is impossible toprove that an infection will never happen, it is important toconsider the potential for transmission and weigh it againstevidence of what is known to have actually occurred.B. Evidence of TransmissionIn creating these guidelines, a review of research was carriedout to examine the documented evidence of HCV transmissionthrough specific practices. Case reports, abstracts andresearch reports were considered, with the greatest weighton reports from cohort studies using multivariate analysistechniques (studying a specific group of individuals overtime and analysing the interaction of a number of variables).For the purpose of this model, greater emphasis is placedon what is known or proven to happen, than on what mayhappen in theory.To assess the risk of HCV transmission, the potentialfor transmission and the evidence that transmission hasoccurred are both considered. Activities are then placed intoone of four categories.Categories for Assessing Risk1. No riskTo our knowledge, none of the practices in this categoryhave ever been demonstrated to lead to HCV infection.There is no potential for transmission since all of the basicconditions for viral transmission are not present.Potential for transmission . . . . . . . . . . . . . . . . . . . . . . NoneEvidence of transmission . . . . . . . . . . . . . . . . . . . . . . None2. Negligible riskAll of the practices assigned this risk level present a potentialfor HCV transmission because they involve an exchangeof blood. However, the amounts, conditions and media ofexchange are such that the efficiency of HCV transmissionappears to be greatly diminished. There are no confirmedreports of infection from these activities.Potential for transmission . . . . . . . . . . . . . . . . . . . . . . . . YesEvidence of transmission . . . . . . . . . . . . . . . . . . . . . . None3. Low riskAll of the practices assigned this risk level present a potentialfor HCV transmission because they involve an exchange ofblood. There are also a few reports of infection attributedto these activities (usually through individual case studiesor anecdotal reports, and usually under certain identifiableconditions).Potential for transmission . . . . . . . . . . . . . . . . . . . . . . . . YesEvidence of transmission . . . Yes (under certain conditions)4. High riskAll of the practices assigned this risk level present a potentialfor HCV transmission because they involve an exchange of38 Hepatitis C Transmission
HIV TRANSMISSION: Guidelines for Assessing Riskblood. In addition, a significant number of scientific studieshave repeatedly associated the activities with HCV infection.Even when the exact mechanism of transmission is notcompletely clear, the results of such studies conclude thatactivities in this category are high risk.Potential for transmission . . . . . . . . . . . . . . . . . . . . . . . . YesEvidence of transmission . . . . . . . . . . . . . . . . . . . . . . . . YesChallenges of Assessing Risk for HCVA. Lack of Consistent Information andResearch on Sexual TransmissionResearch on sexual transmission of HCV shows somediscrepancy between male to male transmission and femaleto male/male to female transmission. There is frequentmention of certain activities (for example: penile-analintercourse, anilingus, using insertive sex toys and sadomasochisticactivities) in the male to male research indicatingthat these activities are consistent with sexual transmission.In female to male/male to female these activities are notmentioned and there is little evidence of sexual transmissionof HCV between men and women. For the purposes ofassessing risk, where there is potential and evidence for atleast one group, the assessment assumes that the conditionsfor transmission have been met for all groups unless thereare physiological differences that warrant a different riskassessment.B. Difficulty Assessing the Risk of a SingleActivity in the Presence of Multiple ActivitiesFor the purposes this model, we consider the risk of a singleepisode of each particular practice. In real life, activityis rarely confined to one episode or to one practice. If acombination or sequence of activities is deemed to increaserisk, these factors are addressed in the text.Hepatitis C Transmission39
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