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HIV Incidence Surveillance (HIS) is an expanded HIV/AIDS surveillance activity funded by the Centers for Disease Control and Prevention (CDC). The objective is to provide national and local population-based estimates of the number of new HIV infections per year.


Incidence Surveillance employs the serological testing algorithm for recent HIV seroconversion (STARHS). Leftover serum from the HIV positive diagnostic specimen is tested with a special assay, the STARHS assay, which is based on HIV antibody characteristics. The STARHS assay measures the probability that an individual was infected with HIV recently. A person's HIV testing and treatment history is gathered in conjunction with the completion of the HIV case report. Both the result of the antibody test and the testing and treatment history of each newly diagnosed person are necessary components of the STARHS algorithm that is used to estimate HIV incidence.

STARHS assay

There have been several STARHS assays used to determine the probability each individual tested was infected with HIV recently. Generally a recent HIV infection is one that occurred within about a half year of HIV diagnosis. The names of the STARHS assays used were the less sensitive EIA (LS-EIA, used from 2000 to 2003), BED (used from 2003 through 2014), and now the Avidity assay (starting in 2014). Because the BED assay was designed solely for surveillance purposes, patient consent is not required and results are not allowed to be returned to patients or their healthcare providers. Laboratories conducting Western blot or other HIV confirmatory tests are requested to submit leftover sera for incidence surveillance. Incidence surveillance is a part of HIV/AIDS case surveillance conducted under Washington Administrative Code legal authority (WAC 246.101).

Testing and treatment history

Information about a person's HIV testing and treatment history is collected for each person who is newly diagnosed with HIV. This information is collected on the adult HIV/AIDS case report form. A person's frequency or pattern of HIV testing is important for knowing the probability that a person would be identified as recently infected.

National HIV incidence

In 2008, the CDC published the first national HIV incidence estimate this methodology. The analyses showed that in 2006, an estimated 56,300 new HIV infections occurred. In 2011 this estimate was updated to 48,600 for 2006; 2007 and 2008 estimates were 56,000 and 47,800 respectively. National data published in 2012 for 2006-2009 indicated that among newly-diagnosed PLWHA for whom previous testing history information was available, 41% were diagnosed with HIV infection at their first HIV test, and 59% had a negative test at some point before HIV diagnosis.

King County HIV incidence

In 2012, WA state published HIV incidence estimates which ranged from 497 to 588 new infections in the state and 319 to 273 infections in King County for 2007 through 2011. (See 2nd Half 2012 Epidemiology report. These numbers were very similar to the numbers of reported cases each year. Relative to national data, King County cases were far more likely to have a prior negative HIV test before diagnosis. Between 2006 and 2009, 83% of individuals with testing history data had a prior negative HIV test and 17% were positive on their first HIV test. In the four subsequent years, 2010 to 2013, that improved slightly to 85% of individuals with a prior negative HIV test and 15% who were diagnosed with HIV at the time of their first HIV test.