Two studies from Europe presented at the 17th Conference on Retroviruses and Opportunistic Infections (CROI) in San Francisco have found that HIV incidence is not decreasing in gay men, and in some populations may be increasing.
The two studies presented were among a number that used various methods of measuring or estimating HIV incidence directly, rather than relying on measures like HIV diagnosis rates, which may not reflect current infection rates.
The studies from Europe contrast with a study from San Francisco that found evidence of a decline in infection in gay men.
In France national HIV case reporting started in 2003. Samples from patients testing positive are also tested with the IDE-V3 incidence assay to detect recent infections. The assay will not produce a positive antibody result till roughly six months after infection and is robust, producing a false recent-infection rate of 0.8%. Presenter Stéphane le Vu commented that the window period was somewhat longer in certain non-B subtypes but that the false recent-infection rate appeared no higher.
It is estimated that there are 150,000 people living with HIV in France, a prevalence rate of 0.35%, and that there were nearly 7000 new HIV infections in 2008, a fall from nearly 9000 in 2003. This represents a national incidence rate of 17 per 100,000 person years or one person in every 5882 infected each year.
The national case reporting programme reports on French versus foreign nationality, clinical stage, risk group, and previous testing history. HIV incidence differed significantly between populations. Men who have sex with men accounted for 48% of infections, and heterosexuals for 51%, of whom 45% were not born in France (53% of women were non-French). Only 1% of infections were in injecting drug users.
The HIV incidence among gay men, as calculated from the assay, was 1006 infections per 100,000 person years – just over 1% a year. This is 59 times the rate seen in the general population. In contrast the annual incidence rates per 100,000 were 354 amongst non-French heterosexual men, 54 in non-French women, 91 in injecting drug users, six in French men and four in French women.
Incidence in all groups except gay men decreased between 2003 and 2008: in foreign-born heterosexuals incident infections declined from an estimated 2600 to 1600, and declined from 3000 to 2000 in French heterosexuals. Infections in injecting drug users also declined slightly. In contrast, there is what Le Vu called “high and stable incidence” in gay men.
HIV incidence increases significantly in Amsterdam gay men under 30
Meanwhile a longitudinal cohort study of gay men in Amsterdam has found that HIV incidence in gay men has been increasing steadily since the introduction of highly active antiretroviral therapy (HAART) in the mid-90s, and has increased the most in young gay men (under 30). Presenter Iralice Jansen said that previous data had shown an increase in diagnoses among gay men, but no evidence of an increase in incidence.
The Amsterdam Cohort Study is a longitudinal cohort study of HIV infection among a group of initially HIV-negative gay men, recruited at regular intervals ever since 1984, at an average age of 29, and tested for HIV every six months thereafter. For this study, the average length of follow-up was six years.
Out of 1627 men included in this study, 215 acquired HIV during follow-up. Incidence was calculated by assuming that the time of HIV infection was midway between a positive test result and the previous negative test. HIV incidence was initially 7.4% a year in 1985 but fell to 1.3% by 1990 and stayed at that level until around 1995-7. Since then it has slowly increased to 2% a year, though the increase does not pass the test of statistical significance (p = 0.1).
However among gay men aged 30 and under, annual HIV incidence, which had been 0.9% in 1997, increased to 3.8% by July 2009. This result was due to a sudden doubling in the level in 2009 – it had been about 2% in 2004-8 – but the increase observed is statistically significant (p = <0.01).
Sexual risk behaviour mirrored the incidence pattern, with an increase in the proportion of men reporting unprotected sex with casual partners from 12% in 1992 to 30% in 2008.
The strongest factors associated with becoming HIV positive were unprotected sex with casual partners (relative risk [RR] 4.74), having over five partners (RR 2.5), having gonorrhoea (RR 5.76), and no tertiary education (RR 2.11). It was estimated that three-quarters of new infections were due to sex with casual partners and only a quarter in steady partners.
However among older gay men, unprotected sex with steady partners was more significant, and three times as many infections were acquired from primary partners between 2003 and 2008 in over-50 year olds than in the late 1980s. The incidence pattern in gay men aged 25 and gay men aged 50 were mirror images of each other: for younger gay men, the year 1995 featured the maximum risk of infection by a steady partner, but by 2009 this risk had declined considerably. Conversely in 50 year olds the maximum risk from a steady partner was reached in 2005.
Dr Jansen commented that the Netherlands had a lower HIV testing rate than many other developed countries: although 88% of sexual health clinic attendees test for HIV, but rates are much lower in gay men who do not attend sexual health clinics.
Remarking on this study in a later seminar on prevention, Dr Ken Mayer of the Miriam Hospital in Rhode Island said “Seeing an increase in incidence this late in a mature epidemic certainly raises some concerns.”
Le Vu S et al. Population-based HIV incidence in France, 2003 to 2008. Seventeenth Conference on Retroviruses and Opportunistic Infections, abstract 36LB, San Francisco, 2010.
Jansen I et al. Increasing trend among young men who have sex with men in Amsterdam: a 25-year prospective cohort study. Seventeenth Conference on Retroviruses and Opportunistic Infections, abstract 35, San Francisco, 2010.