The risk of sexually transmitting a chronic hepatitis C infection to a long-term monogamous heterosexual partner is very low, averaging just about 1% per year.
That risk level works out to a transmission rate of about one in every 190,000 sexual contacts, Dr. Norah Terrault and her colleagues reported in the April issue of Hepatology (2013;57:881-9).
The cross-sectional study also found that no one sexual practice – including anal intercourse or intercourse during menses – significantly increased the risk of transmission, wrote Dr. Terrault of the University of California, San Francisco. The findings can be used to provide "unambiguous and reassuring counseling messages," she and her coinvestigators noted.
Courtesy U.S. Dept of Veterans Affairs
Hepatitis C is rarely transmitted between long-term monogamous heterosexual partners, said Dr. Norah Terrault.
The study included 500 subjects with chronic HCV infections, and their sexual partners. All couples reported longtime, monogamous relationships (median duration, 15 years); however, the relationship duration varied widely, spanning 2-52 years.
Each of the partners was interviewed separately about their sexual contacts and practices. At the time of interview, the index subjects were a median of 49 years old and the partners, a median of 48 years.
The HCV-positive subjects reported the highest incidence of past risk factors, including blood transfusions before 1992 (32%), injected illegal drugs (54%), and being stuck by a bloody sharp item in a hospital (4%). Nearly half (46%) reported having had at least 20 lifetime sexual partners, with 21% having had 50 or more.
However, partners also reported some risk factors: 11% had an early transfusion, 2% used illegal drugs, and 2% had a hospital sharps incident. Many (27%) also reported having had at least 20 sexual partners.
Among the 500 couples, 20 partners (4%) were coinfected with HCV. Of these, nine were concordantly infected, eight discordantly, and three were indeterminate.
Six of the concordant couples underwent phylogenetic typing. Three were infected with the same HCV isolate and three with different strains. The investigators estimated the time of transmission and any additional risk factor among the three couples with concordant strains.
For the first couple, with an 18-year relationship, transmission probably occurred after about 6.5 years. The female partner had a history of injected drug use, while the male had no identifiable risk factors.
The second couple had a 28-year relationship; transmission probably occurred at around 15 years, the investigators said. "The female partner had a history of injectable drug use and both partners reported more than 20 prior sexual partners, a history of sexual transmitted diseases, and a history of snorting of drugs."
For the third couple, who had been together for 10 years, transmission probably occurred at around year 6. "The male partner had a history of injectable drug use, of being stuck by a sharp bloody object while working in a hospital, and more than 20 prior sexual partners; both partners reported snorting drugs and sharing snorting equipment."
The investigators determined that these infections were probably sexually transmitted between the partners – a prevalence of about 1%. "The estimated risk per sexual contact ranged from 1/380,000 to 1/190, 000," they said.
However, they were unable to identify any behaviors that significantly increased the risk of transmission. Compared with couples without coinfection, coinfected couples were more likely to have vaginal intercourse during menses (100% vs. 66%), more likely to have anal intercourse (67% vs. 30%), and less likely to use condoms (0% vs. 30%), but none of these differences was statistically significant.
"HCV transmission by sex from chronically infected persons to their heterosexual partners in a long-term monogamous relationship likely occurs, but is a rare event," the authors concluded. "Our results provide a basis for specific counseling messages that clinicians can use with their patients... [that] support the current national recommendations that couples not change their sexual practices if they are in a monogamous heterosexual relationship."
None of the study authors reported any financial conflicts.