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Test-and-treat strategies for HIV prevention involve early diagnosis and linkage to care, retention in care, and sustained antiretroviral therapy (ART) in order to increase the proportion of patients with undetectable viral load. For test-and-treat to be successful, a person who is HIV-infected must experience a sequence of events beginning with diagnosis, proceeding through engagement in medical care, and culminating in an undetectable viral load. Gardner, et al, called this the "spectrum of engagement in care." (1)


Gardner used findings from published literature to specify the proportion of living cases who were undiagnosed and those who were subsequently linked to care, retained in care, on ART and had undetectable viral load. We used data reported to the Oregon STD/HIV/TB Program to specify these proportions based on observations in Oregon.* (Figure 1)




Figure 1: Stage of Engagement in HIV Care among Oregon residents, 2011

Estimates of the number of people infected with HIV at each stage of Gardner's spectrum of care from infection to undetectable viral load based on cases living in Oregon as of December 31, 2011 (n=6,066)



Oregon has no independent estimate of the number of persons with undiagnosed HIV infection. The Centers for Disease Control and Prevention (2) estimated that 18.1 percent of people infected with HIV in the U.S. have not yet been diagnosed. If 18.1 percent of people with HIV infection in Oregon have not yet been diagnosed, then the 6,066 reported cases believed to have been living in Oregon in December 2011 represented 81.9 percent of all people with HIV infection in Oregon. This suggests that there were 7,406 people living with HIV in Oregon in 2011, 1,340 of whom were unaware they were infected. **


If a known HIV case had a CD4 T-lymphocyte count or viral load reported to the Oregon HIV/STD/TB Program, then that was assumed to represent a health care visit for HIV. Using this assumption, 96 percent of known cases diagnosed in Oregon had a health care visit within a year of the date of diagnosis and 93 percent had a health care visit within three months of diagnosis. Gardner used a much lower estimate of 75 percent of known cases having a health care visit within a year of diagnosis.


Next we estimated the number and proportion of people retained in care as the number of cases living in Oregon that had at least one reported test (could be either a CD4 T-lymphocyte count or viral load) during 2011. Applying this definition, we found that 88 percent of resident cases were retained in care, again higher than the Gardner estimate of 50 percent. Based on data from Ryan White funded clinics in Oregon, 87 percent of Oregon patients were on ART compare to the 75 percent U.S. estimate used by Gardner. We found that 69 percent of residents with known HIV infection had a suppressed viral load (defined as a viral load of 200 or fewer copies per milliliter of blood) at the time of their most recent test and 57 percent had undetectable viral loads (defined as fewer than 48 copies per milliliter of blood). Gardner used an estimate of 80 percent having undetectable viral loads among those on ART, which resulted in an estimate of only 24 percent of living cases having an undetectable viral load.


Test-and-treat strategies seek to increase the proportion of patients with undetectable viral load in order to reduce HIV transmission. The Oregon HIV diagnosis rate has decreased to levels not seen since the mid-1980s (Figure 2). Decreases in HIV diagnoses are likely due to (a) advances in medical care and adherence to ART, (b) financial and support services that allow sustained access to medical care, and (c) early diagnosis and reducing the risk of infecting others.


Figure 2: HIV diagnosis in Oregon, rates per 100,000, 1981–2011



In summary, we found that linkage to care and retention in care was high in Oregon and may reach a ceiling. However, this analysis points to some opportunities for improvement in Oregon:


  • There is a need for a reliable and valid estimate of people infected with HIV but not yet diagnosed;
  • Oregon should continue to try to reduce the number of people with undiagnosed HIV infection;
  • Oregon would likely reduce the number of new infections by reducing the time from infection to diagnosis through the work of disease intervention specialists and by more widespread testing;
  • Oregon would likely reduce the number of new infections by reducing the interval between diagnosis and viral load suppression.


* Case residence was determined by (a) current ADAP residence or residence at the time of their most recent CD4 and viral load test and (b) if cases had a CD4 or viral load (2007–2011). Cases first diagnosed outside Oregon may not have been linked to care at the same rate as new diagnoses in Oregon, which was the sample used to estimate that 96 percent of diagnoses (2007–2010) were linked to care in one year.


**The estimate of 6,066 reported cases living in Oregon does not include cases originally reported in Oregon who have subsequently moved to another state or country. The estimate does include cases that were originally reported in another state who live in Oregon. The proportions that Oregon observed who were retained in care, , on ART, and who have undetectable viral loads, were based on resident cases. The proportions Gardner used did not control for people who moved to another state after diagnosis or moved into a state since diagnosis. Consequently, the Gardner estimates probably underestimate the numbers and proportions of people who met or exceed the threshold for various levels of the spectrum because they might very well have received care and had laboratory testing in another state that was not reported to the state where the case was originally reported.



(1) Gardner et al, ‘The Spectrum of Engagement in HIV Care and its Relevance to Test-and-Treat Strategies for Prevention of HIV Infection’ Clin Infect Dis. 2011 Mar 15;52(6):793-800.


 (2) Centers for disease Control and Prevention. Monitoring selected national HIV prevention and care objectives by using HIV surveillance data—United States and 6 U.S. dependent areas—2010. HIV Surveillance Supplemental Report 2012; 17(no. 3, part A). Published June 2012 Accessed June 22, 2012. Note: web resource moved from location. Document re-located May 9, 2016 here: