About 50,000 adults a year are being infected with HIV in the US, a new estimate by the country’s Centers for Disease Control (CDC) revealed today in an article in the open-access journal PLoS One.
This infection rate, equating to an annual incidence of 0.019% or about one infection a year in every 2000 US citizens over 13, has stayed steady in the last four years for which we have complete figures (2006 to 2009).
However, this unchanging incidence conceals large increases in the new infection rate in young people, gay men, black men, and particularly the group including all those categories – young, black, gay men.
Between 2006 and 2009, new HIV infections increased by 20.5% in young people aged 13 to 29, by 34% in young gay men, by 43% in young black men, and by 48% in young, black, gay men.
The CDC’s estimate is based on extrapolations of figures from surveillance areas in 16 states and two cities which use an incidence assay to estimate the proportion of newly diagnosed cases of HIV that are recent infections (in the last six months). These surveillance areas cover 65% of the US population, though some significant high-prevalence HIV areas are omitted, including California and the District of Columbia.
It then calculates how many new HIV infections there are per year – both diagnosed and undiagnosed – in the whole country. This task has been made easier since 2008 when all states began to participate in anonymised name-based reporting of all new HIV diagnoses.
New diagnoses are not the same as new infections, as it could be picking up on infections that occurred many years ago. However, the CDC finds that, despite its own campaign to standardise HIV testing in primary care, in emergency rooms and in high-prevalence areas, the number and frequency of HIV tests performed in the US did not increase between 2006 and 2009. Because of this, any increase in diagnoses is more likely to reflect actual increases in incidence, rather than the diagnosis of more long-term infections in previously untested people. The CDC estimates now that only one-in-five people with HIV in the USA – 21% – is undiagnosed, but that the undiagnosed may still be transmitting the majority of new infections.
The detailed figures in the report include:
- There were 31,162 new diagnoses (allowing for late reports) in the surveillance areas in 2009. This was more or less the same as in 2006. There was a significant rise in diagnoses in 2007 – why is not clear – but whole-population figures then declined in the next two years.
- Extrapolating these figures to the whole country and including the undiagnosed would mean that there were 48,100 new HIV infections in the whole US in people over 13 in 2009.
- A steady 56.5% of people who tested positive had had a previous HIV-negative test and, amongst those, 42% (24% of all diagnosed) had had a negative test less than a year previously. The percent classified as having been infected in the last six months according to the incidence assay was a consistent 31% of all diagnosed.
- Three-quarters of new infections were in men, 44% in African-Americans (who make up 12.5% of the population) and, in 2009, 61% were in men who have sex with men (MSM).
- Infections increased significantly in young people aged 13 to 29 in the four years of the survey, from 15,600 in 2006 to 18,800 in 2009 (a 20% increase). However, this increase only remained significant in young African-American men, where infections rose from 5300 in 2006 to 7600 in 2009 (a 43% increase).
- Infections in MSM increased from 27,000 to 29,300 in the four years – a non-significant increase of 8.5%. When analysed, the increase in MSM only remained significant in black MSM, where new infections increased by 20% from 9000 to 10,800 in the four years, and in young MSM aged 13 to 29, where infections increased by 34% from 9600 in 2006 to 12,900 in 2009.
- When this was broken down further, the majority of this increase was in black MSM aged 13 to 29, where new infections increased from 4400 in 2006 to 6500 in 2009 – a 48% increase. This accounts for almost all the increase in new infections in gay men.
- The highest rate of infections in Hispanic gay men also occurred in the 13 to 29 age group, though it showed no sign of increase, but the highest infection rate in white men was in the 30 to 49 age range.
“The estimates for 2006-2009 continue to underscore the disproportionate toll that the HIV epidemic has taken... on racial/ethic and sexual minorities,” comments the CDC.
“Adequate funding and services should be directed to individuals at greatest risk for acquiring and transmitting HIV infection, if we are to make a further impact on the HIV epidemic in the United States,” it concludes.
Prejean J et al. Estimated HIV incidence in the United States, 2006-2009. PLoS One 6(8) e17502. doi:10.1371/journal.pone.0017502, early online edition, August 2011.