Sexually transmitted infection (STI) could be considered a high-risk category for HIV transmission through organ donation. But hemophilia should now be dropped as a risk category, given the low incidence of HIV in that population, according to a study presented at the American Transplant Congress in Philadelphia in May.
The U.S. Centers for Disease Control and Prevention (CDC) issued classifications of high-risk organ donors in 1994, but the epidemiology of certain infections has changed since then. Current evidence shows that STI could now be considered a high-risk category, given the high incidence and prevalence of HIV among this population. But given the very low 1 in 100,000 incidence of HIV among people with hemophilia, it should be dropped as a high-risk category, said Lauren Kucirka, ScM, an epidemiologist in the department of surgery at the Johns Hopkins University School of Medicine in Baltimore.
The CDC currently categorizes potential donors as being at high risk on the basis of seven behaviors or circumstances. These individuals include men who have sex with men, injection drug users, people with hemophilia, commercial sex workers, people who have high-risk sex (that is, with people in any of the foregoing groups), people who have been exposed to HIV through blood, and people who are incarcerated.
By these criteria, about 9 percent of donors from whom at least one organ is recovered are classified as being at high risk, and these organs are 26 percent more likely to be discarded than are those from donors not at high risk. Kucirka noted that the CDC guidelines have several limitations: they were designed in 1994, before the advent of highly active antiretroviral therapy; they were aimed in part at HIV but have been extended to hepatitis C virus (HCV) infection; and although they were designed to identify donors at risk of prevalence infection, the real risk from HIV is from incident infection. In the case of hemophilia, for example, the prevalence of HIV is high among people who received transfusions in the 1980s, but because of tests to screen blood the incidence of new infections is low.
To investigate potential new high-risk categories, Kucirka and colleagues performed a systematic review of the literature on the incidence and prevalence of HIV and HCV from 1995 through 2008, as well as a meta-analysis. They identified 272 eligible abstracts for HIV estimates and 218 for HCV estimates.
Window period
A “window period” exists between the time of an infection and when it is detectable by laboratory methods. All donors are screened for infectious diseases, but they will falsely test negative if they are in the window period and may then transmit an infection to one or more recipients. “The window period using nucleic acid testing for diseases like HIV and hepatitis C is about a week,” Kucirka said.
From the abstracts, the investigators were able to calculate a “risk of window-period infection” for HIV. For the current CDC categories, “the incidence ranged from two infections per 100 person-years for injection drug users to less than 1 per 10,000 person-years for hemophiliacs,” she said.
On the basis of a review of the abstracted data, the authors discerned subgroups of the population with a high incidence of HIV or HCV. Body piercings, tattoos, or intranasal cocaine use did not appear to confer any increased incidence in comparison with control individuals from the same study populations.
“And finally we looked at STI,” Kucirka said. “So we found among those who were positive for [any] STI a pooled incidence of 1.7 per 100 person-years, which was similar to the incidence in men who have sex with men and injection drug users and would result in an expected number of 4.2 window-period HIV infections per 10,000 donors.” Compared with their peers from the same study population, people with STIs had about twice the prevalence and twice the relative incidence of a window-period HIV infection.
“Addition of new categories should be approached with caution, particularly in light of the high discard rate when a donor is classified as at high risk,” Kucirka advised. Nonetheless, STI could be considered a potential high-risk category, given the high incidence and prevalence of HIV infection in this category. But given the very low incidence among people with hemophilia, this category “could potentially be dropped,” she said.
The CDC is currently formulating new guidelines and will put them out for comment soon.
“We’re operating based on some assumptions that were made in 1994 that were clearly obsolete at this point and inappropriate in some settings and don’t reflect either the available testing or the changing demographics of blood-borne pathogens like HIV and hepatitis C and hepatitis B,” said Emily Blumberg, MD, professor of medicine and director of transplant infectious diseases at the University of Pennsylvania in Philadelphia and chairperson of the ad hoc disease transmission advisory committee of the Organ Procurement and Transplantation Network.
She emphasized that the field has an excellent track record, citing the transmission of only two HIV infections from deceased donors and one from a living donor since 1987. “We’re all trying to figure out how to make all of these things even safer,” she said.
