HIV Incidence Surveillance

Prevalence vs. Incidence
The prevalence of HIV/AIDS includes all people living with HIV and AIDS, regardless of when they acquired their infection. The prevalence is expressed as a percentage of the population at a point in time.

HIV incidence is the number of new HIV infections in a specific population during a specific time period.

It is important to remember that a new HIV diagnosis does not necessarily mean a new infection. Many people only find out they are infected years after their initial infection.

Why is the incidence of HIV important?
With more HIV tests being performed each year, an observed increase in HIV diagnoses may no longer indicate that there may have been an increase in the number of new HIV infections over the same period.

It has become important to distinguish between recent and long-standing HIV infection on the population level and to expand the HIV surveillance system to include both incidence and prevalence.

Accurately measuring incidence can help us understand how HIV is spreading now and where to more effectively focus prevention efforts.

Incidence estimates can also help us measure our progress in reducing the spread of HIV in Florida over time.

How does HIV incidence surveillance work?
A major advance has been the development of the Serologic Testing Algorithm for Recent HIV Seroconversion (STARHS). STARHS may distinguish between recent and long-standing HIV infection on a population level.

The STARHS method works by comparing two HIV enzyme-linked immunosorbent assays (EIA). The first EIA is the standard test used for routine diagnosis which detects very low levels of antibodies.

The second step of STARHS is conducted only on HIV positive sera. The assay is sensitive to the length of time since the infection (i.e., antibody level present). Because a person’s level of antibody gradually increases in the early stages after infection, the result of the second test suggests whether they have been infected for a shorter (~ months or less) or longer time.

The assay used is the Calypte HIV-1 BED Capture EIA, which is approved only for surveillance use because it is only accurate at the population level. Under FDA regulations, results of STARHS performed for purposes of HIV incidence surveillance cannot be returned to individuals or their health care providers or used for clinical management.

What specimens are tested with STARHS?
Florida implemented STARHS in public counseling and testing sites in 2004. In November 2006, Florida added STARHS to the list of reportable conditions in Chapter 64D-3, Florida Administrative Code (F.A.C). All private and commercial laboratories that provide diagnostic testing for HIV must submit a specimen for STARHS testing.

What else is needed to measure HIV incidence?
Information on testing behavior is needed, such as recency of testing and testing frequency. Additionally, history of antiretroviral use is collected. Testing and antiretroviral use history information is gathered as part of a comprehensive HIV counseling session.

Estimating HIV incidence
HIV incidence is estimated using the number of infections identified as recent among those individuals who chose to have an HIV test, test positive, and are newly reported to the HIV/AIDS Reporting System (HARS). This sample along with demographic data and the testing and treatment history is used to estimate HIV incidence in the population.

The Centers for Disease Control and Prevention (CDC) released new incidence estimates in the August 3, 2011 edition of the online scientific journal PLoS ONE 02 Using a refined estimation methodology, different from the one presented in 2008, CDC re-estimated new HIV infections in the United States for 2006, as well as presenting new estimates for 2007, 2008, and 2009.

In 2006 there were an estimated 48, 600 new infections in the United States (95% confidence interval: 42,400-54700)
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)

These estimates showed that the annual number of new infections was overall stable from 2006 through 2009. Even though the analysis shows overall stability in new HIV infections in recent years, the HIV/AIDS epidemic remains at an unacceptably high level.

Florida HIV Incidence Estimates
Using CDC’s revised methodology, the HIV/AIDS and Hepatitis program was unable to recalculate an incidence estimate for 2006; estimates for 2007, 2008, and 2009 were calculated.

In 2007 there were an estimated 5,307 new HIV infections in the state of Florida ((95% confidence interval: 4,447-6,143)
In 2008 there were an estimated 5,541 new HIV infections (95% confidence interval: 4,584-6,499)
In 2009 there were an estimated 4,577 ne HIV infections (95% confidence interval: 3,712-5,442)

The new estimates show an average 33 per 100,000 people living in Florida were newly infected with HIV across all three years. This rate is 60 percent higher than the average national rate of 20 per 100,000.

Compared to the national estimates, Florida’s most highly impacted groups are similar. In Florida, in each year the most new infections occurred in males (accounting for 71%, 72%, and 74% of new infections respectively), Black/African American (46%, 47%, and 46%), and men who have sex with me (MSM) (54%, 48%, and 53%)

As in the national estimates, Florida’s infection rates per 100,000 demonstrate significant disparities. Most notable is the disproportionate burden of disease between racial/ethnic groups. In Florida, Black/African Americans and Hispanics have average rates that are six and two times the rate of Whites. The rate of new infections is highest among individuals were between the ages of 30-39 years of age at the time of infection (65 per 100,000, 61 per 100,000 and 55 per 100,000 for years 2007-2009 respectively).

For risk of transmission, MSM have the highest percentage of new infections for all three years (50%, 50%, and 53%). Heterosexual and other risk behavior accounted for the second highest risk.

The 2007-2009 Florida HIV incidence estimates highlight the populations currently at greatest risk of HIV infection. The estimates will help us focus our prevention strategies and allocate funding accordingly. As more data is collected, it will become easier to track Florida’s HIV incidence trends and adapt our prevention strategies as warranted.

For additional information, please contact Mariama Gondo, MPH at (850) 245-4444, extension 2568.

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