HIV incidence is the measure of new HIV infections in a given period. In recent years, CDC has used new technology and methodology to more directly measure the number of new HIV infections in the United States. These incidence estimates are used to monitor the HIV epidemic in this country, and to guide policies and programs created to serve those communities and populations most affected by HIV.

CDC published new incidence estimates in the August 3, 2011, edition of the online scientific journal PLoS ONE using a refined methodology that allowed for a more precise 2006 incidence estimate (previously 56,300) as well as new estimates for 2007, 2008, and 2009. These new estimates showed that the annual number of new HIV infections was stable overall from 2006 through 2009.

• In 2006 there were an estimated 48,600 new HIV infections in the United States (95% confidence interval: 42,400-54,700)
• In 2007 there were an estimated 56,000 new HIV infections (95% confidence interval 49,100-62,900)
• In 2008 there were an estimated 47,800 new HIV infections (95% confidence interval: 41,800-53,800)
• In 2009 there were an estimated 48,100 new HIV infections (95% confidence interval: 42,200-54,000)

Even though the annual number of new HIV infections was stable overall during those years, there was an estimated 21% increase in HIV incidence for people aged 13-29 years, driven by a 34% increase in young MSM (the only group to experience a significant increase in incidence in this age range). Among MSM aged 13-29, HIV incidence among black/African American MSM increased significantly (48%) from 2006 through 2009 with a statistically significant 12.2% estimated annual percentage increase.

The reasons for this increase are not fully known, but may include a high background prevalence of HIV in black MSM and societal factors, including stigma of HIV and homosexuality, limited access to health care, and poverty that may create an enabling environment for HIV infection.

Overall, CDC’s new incidence estimates continue to show that

• Gay and bisexual men remain the population most heavily affected by HIV in the United States. CDC estimates MSM represent approximately 2% of the US population, but accounted for more than 50% of all new HIV infections annually from 2006 to 2009 –56% in 2006 (27,000), 58% in 2007 (32,300), 56% in 2008 (26,900) and 61% (29,300) in 2009.
  

• African Americans and Hispanics/Latinos are the racial/ethnic groups most affected by HIV. African Americans represent approximately 14% of the US population, but accounted for 44% (21,200) of all new HIV infections in 2009. Hispanic/Latinos represent approximately 16% of the total US population, but accounted for 20% (9,400) of all new HIV infections in 2009.
  

  Overall, in 2009, African American men had the highest rate of new HIV infections (103.9 new infections per 100,000 persons), followed by Hispanic/Latino men (39.9 per 100,000), and African American women (39.7 per 100,000).

Resources for HIV incidence

• Fact sheet: Healthy People 2020 Leading Health Indicators Objective HIV-13: Proportion of Persons Living with HIV Who Know Their Serostatus
• Prejean J, Song R, Hernandez A, Ziebell R, Green T, et al. (2011) Estimated HIV Incidence in the United States, 2006-2009. PLoS ONE 6(8): e17502.doi:10.1371/journal.pone.0017502
• Fact sheet: Estimates of New HIV Infections in the United States, 2006-2009
• Fact sheet: HIV in the United States: An Overview
• Fact sheet: Highlights of CDC Activities Addressing HIV Prevention among African American Gay, Bisexual, and Other Men Who have Sex with Men
• Surveillance Brief: Surveillance Systems Supported by the Division of HIV/AIDS Prevention
• Surveillance Brief: Terms, Definitions, and Calculations Used in CDC HIV Surveillance Publications
• Slide Set: HIV Incidence in the United States 2006–2009
• Consultation Summary: Consultation on Advancing HIV Incidence Surveillance Summary