Overall, users of PEP were almost four times more likely to become infected with HIV than gay men who did not use the therapy.
There was no evidence that PEP failure was the cause. The investigators believe this is because PEP users continued to put themselves risk of HIV after completing their treatment.
“Our study showed a high incidence of HIV among MSM [men who have sex with men] who used PEP, an indication of ongoing risk behaviour,” write the investigators. “This implies that PEP alone for this group is not sufficient to prevent HIV infection, and a combination of other more comprehensive preventative strategies is needed.”
HIV post-exposure prophylaxis is a four-week course of combination antiretroviral therapy, prescribed after an encounter with body fluids possibly infected with HIV.
It is estimated that the treatment can reduce the risk of infection by up to 81%.
Gay men are the group most likely to request PEP after a possible sexual exposure to HIV. Australian research has shown that gay men who used PEP continued to be at risk of HIV after completing their treatment.
Therefore, Dutch investigators compared HIV incidence among gay men prescribed PEP in Amsterdam between 2000 and 2009, and compared this to the rate of new infections seen over the same period among gay men enrolled in the Amsterdam Cohort Study.
A total of 355 men who received 395 PEP prescriptions were included in study. The majority of individuals took one course of PEP, but approximately 10% of men were provided with multiple prescriptions (two to four).
Adherence rates were high, with 94% of men completing their therapy. HIV status was monitored three and six months after baseline.
Eleven PEP users seroconverted. Two men tested HIV-positive at their three-month follow-up appointment; one individual who did not attend for his three month appointment was diagnosed at month six; and the remaining eight men were HIV-negative at month three, but were HIV-positive at month six.
This provided an HIV incidence of 6.4 per 100 person years among the individuals treatment with PEP.