"Tentative" may be the kindest word to describe Centers for Disease Control and Prevention (CDC) online statements about sexual transmission of HCV. The CDC does recommend testing some gay and bisexual men for HCV infection, but in a statement that starts with a negative clause: "Testing for Hepatitis C is not recommended for gay and bisexual men unless they were born from 1945 through 1965, have HIV, or are engaging in risky behaviors."1
That fact sheet for gays, as well as CDC advice for professionals, make sexual transmission of HCV seem almost an anomaly: "While rare, spreading Hepatitis C through sex is possible."2
The CDC's longest fact sheet declaration on HCV transmission clearly states that "HCV is most efficiently transmitted through large or repeated percutaneous exposure to infected blood (e.g., through transfusion of blood from unscreened donors or through use of injecting drugs)."3 No one would argue with that. This transmission summary goes on to note that "although much less frequent, occupational, perinatal, and sexual exposures also can result in transmission of HCV." Sexual transmission takes third place in this list of "much less frequent" transmissions, though overwhelming evidence from the past decade documents an explosive HCV epidemic among men who have sex with men (MSM) throughout the United States, Europe, and Australia. No research suggests occupational or perinatal HCV transmission has grown at anywhere near the riptide pace seen in gay and bisexual men with and without HIV.
The most recent opportunistic infection guidelines from the CDC, National Institutes of Health, and HIV Medicine Association better reflect current research in MSM.4 "In HIV-infected MSM," this document notes, "multiple outbreaks of acute HCV infection demonstrate that sexual transmission is an important mode of acquisition in this population," adding that risk factors include condomless receptive anal intercourse, using sex toys or noninjection recreational drugs, and sexually transmitted infections (STIs).
In these guidelines the CDC recommends routine HCV testing for "all HIV-infected patients."4 For "at risk HCV-seronegative persons," the CDC advises HCV antibody testing "annually or as indicated by risk exposure." A positive antibody result calls for confirmatory HCV RNA testing to identify chronic -- versus cleared -- HCV infection.
But if a provider or layperson clicks their way to handy HCV summaries at the CDC website,1-3 they may easily come away with the impression that HCV jumps from one sex partner to the other too rarely to justify routine testing.
The perception that HCV seldom roves between sex partners reflects some U.S./Canadian research from the early 2000s in MSM and people with HIV.5-7 But other research from that era -- and volumes of more recent work -- amply demonstrate an epidemic of sexually transmitted HCV in MSM. Studies that identify transmission risk factors show why gay sex poses a much higher HCV transmission risk than heterosexual sex: it can be bloody. Rough anal sex, including sex toy use and fisting (inserting the fist into the rectum), and high rates of lesion-producing STIs offer HCV a direct route to the bloodstream and target cells throughout the body. Injection drug use and unscreened transfusions pose the highest risk of HCV transmission because big loads of blood carry more HCV than small loads. Less blood -- often no blood -- flows between partners during sex, but more blood typically gets mixed during gay sex than straight sex. Semen can also carry HCV RNA.
A clever analysis by Swiss HIV Cohort Study (SHCS) investigators offers strong evidence that, within HIV transmission pairs, having an HCV-positive sex partner doubles the risk of getting infected with HCV.8 The SHCS team turned to its antiretroviral resistance database and compared HIV genetic sequences to find 1555 HIV transmission pairs with known HCV status. Most pair members (78.5%) were men. Almost half (48.5%) picked up HIV during sex between men, while about one quarter became infected heterosexually and one quarter when injecting drugs.
Within likely HIV transmission pairs, having an HCV-positive partner boosted odds that the second partner would also have HCV more than 13 times (odds ratio [OR] 13.6, 95% confidence interval [CI] 10.5 to 17.6).
These higher odds held true when the researchers considered HIV transmission groups separately: 3.1 (95% CI 1.4 to 7.0) for MSM, 4.5 (95% CI 1.2 to 16.3) for MSM who injected drugs but attributed their HIV to sex, 5.4 (95% CI 2.9 to 10.3) for heterosexuals, 2.1 (95% CI 0.9 to 5.1) for heterosexuals who injected drugs but attributed their HIV to sex, and 2.7 (95% CI 1.3 to 5.5) for injection drug users (IDUs). Overall chances of having HCV if one's sex partner has HCV remained significant after statistical adjustment for HIV transmission group, calendar year, age, and sex (OR 3.2, 95% CI 2.2 to 4.7).
The SHCS team figured HCV incidence (the new-infection rate) by determining how many members of a likely HIV transmission pair tested negative for HCV then later tested positive. HCV-negative people who belonged to an HIV transmission pair in which the partner already had HCV proved twice as likely to acquire HCV infection as HCV-negative pair members whose partner did not already have HCV (hazard ratio [HR] 2.1, 95% confidence interval 1.1 to 3.8). This analysis adjusted for HIV transmission risk factor and calendar year.
The researchers stressed that their study does not involve confirmed sex partners: They relied on HIV phylogenetic analysis to infer partnerships (a well-accepted technique), and they did not phylogenetically analyze HCV in likely HIV pairs. The authors cautioned that the results may not apply to other HIV populations, but other Western HIV populations share more similarities than differences with the Swiss population. The twice higher risk of picking up HCV if a sex partner has HCV encouraged the SHCS team to underline "the importance of safe sex practices in HCV-discordant MSM couples and in sex with unknown partners even if HIV is suppressed by highly active antiretroviral therapy."8
The CDC's own research provides evidence strongly implicating sexual transmission of HCV in the United States. CDC analysis of 30,074 National Health and Nutrition Examination Survey (NHANES) participants from 2003 and 2010 identified illicit drug use (including injecting drugs) and getting a blood transfusion before 1992 as predictors of chronic HCV infection.9 Yet 49% of HCV-infected people in this analysis did not report either risk factor, a result leading the CDC team to propose that "risk-based screening alone is an incomplete approach to identifying chronically infected persons."
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