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Viral load above 1500 copies 23% of time in CDC study of 6 clinics
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CROI 2015, February 23-26, 2015, Seattle, Washington
Mark Mascolini
Webcast:
http://www.croiwebcasts.org/console/player/25694?mediaType=slideVideo&
HIV-positive people in care in six US clinics spent one quarter of follow-up time with a viral load above 1500 copies, a level that heightens risk of HIV transmission [1]. Centers for Disease Control and Prevention (CDC) researchers identified several groups more likely to have weeks pass with a viral load topping 1500 copies: younger people, blacks, people without private insurance, and people with more than 6 months between viral load tests.
The test-and-treat principle rests on findings that people with very low viral loads have a negligible risk of transmitting HIV to sex partners. CDC researchers conducted this study to measure person-time that HIV-positive people in care spend with a viral load above 1500 copies, citing research showing that people with lower loads are unlikely transmitters [2,3].
The study involved 14,532 HIV-positive people in care at clinics in Baltimore, Birmingham, Boston, Brooklyn, Houston, and Miami. Everyone (1) received care at some time between April 1, 2009 and March 31, 2013, (2) had two or more viral load tests at the clinic in a 4-year period, and (3) had their first viral load test no later than April 1, 2012.
The CDC team calculated the number of days spent with a viral load above 1500 copies relative to total days in which their viral load was observed. By dividing days with a viral load above 1500 by total days of observation, the researchers reckoned person-time spent above the 1500-copy threshold. They figured that all days between two sub-1500 results were sub-1500 days, and all days between two 1500-plus results were above 1500. When one result was above 1500 and the adjacent result below, they estimated person-time above 1500 as the size of the difference in the two viral loads and the extent to which the larger viral load exceeded 1500. The researchers used Poisson regression analysis to identify predictors of days above 1500 copies.
A large majority of this group, 90.5%, took antiretroviral therapy (ART) at some point during the study period. Median time between the first and last viral load test measured 1073 days and ranged from 30 to 1459 days. Median number of viral loads per patient was 9 and ranged from 2 to 40.
Overall study participants spent 23.1% of viral load observation time with a load above 1500. That means each person, on average, spent 84 days a year--almost 3 months--with a 1500-plus viral load. Just more than half of these people, 54%, spent some time with a load above 1500, while the remaining 46% always had a sub-1500 load.
Percent of time with a viral load above 1500 was 32.1% in 16- to 39-year-olds (adjusted rate ratio [aRR] 1.38 vs 50- to 85-year-olds, P < 0.001), 22.8% in 40- to 49-year-olds (aRR 1.18 vs 50- to 85-year-olds, P < 0.001), and 16.5% in 50- to 85-year-olds. Blacks spent 26.1% of observation time with a viral load topping 1500 (aRR 1.24 vs whites, P < 0.001), Hispanics spent 19.7% of time above 1500 copies, and whites spent 16.0% of time in over-1500 territory. Women spent 25.1% of observation time above 1500 copies, heterosexual men 23.6% of time, and gay/bisexual men 20.1% (aRR 0.94 vs heterosexual men, P = 0.024).
Study participants who had 6-month gaps between fewer than 10% of viral load pairs spent only 15.7% of person-time above 1500 copies, compared with 25.5% by people with 6-month gaps between 10% to 25% of viral load pairs (aRR 1.52 vs fewer than 10%, P < 0.001) and 34.4% by people with 6-month gaps between more than 25% of viral load pairs (aRR 2.04 vs reference group, P < 0.001).
People using private insurance spent only 13.1% of their time with a viral load above 1500 copies, compared with 16.1% by Medicare patients (aRR 1.23 vs private insurance, P < 0.001), 25.5% by Medicaid recipients (aRR 1.39 vs private insurance, P < 0.001), and 28.4% by Ryan White or charity dependents (aRR 1.29, P < 0.001).
Patients whose first viral observed in the study stood above 1500 copies spent 50.8% of time with a viral load above 1500 copies, while people with a sub-1500-copy first-time load spent only 10.5% of observation time atop the 1500 mark (aRR 4.03 for first load above versus below 1500, P < 0.001). Boston residents spent the least time with viral loads above 1500 (14.5%), while Houston inhabitants spent 27.8% of time atop 1500 (aRR 1.30 vs Boston, P < 0.001) and Miami denizens 26.8% (aRR 1.56 vs Boston, P < 0.001). For the other cities, percent of time above 1500 was 16.3% in Birmingham, 18.8% in Brooklyn, and 21.5% in Baltimore.
People not taking antiretrovirals saw 57.6% of follow-up time pass with more than 1500 copies (aRR 2.70 vs on ART at start, P < 0.001). Those who began treatment during follow-up spent 45.4% of time with a load above 1500 (aRR 2.09 versus on ART at start, P < 0.001), and those on ART when follow-up started spent 21.4% of time with a viral load above 1500.
The CDC team proposed person-time with a viral load above 1500 could offer a new way to look at HIV transmission that supplants the standard snapshot of percentage of patients having a detectable viral load at a single point. They stressed that "minimizing the number of viral load tests with intervals greater than 6 months may reduce person-time above the [viral load\] threshold, lower transmission risk, and benefit patients' health."
References
1. Gardner LI, Mark G, Rose C, et al. Time above 1500 copies/mL: a viral-load measure for assessing transmission risk of HIV-positive patients in care. CROI 2015. February 23-26, 2015. Seattle, Washington. Abstract 101.
2. Quinn TC, Wawer MJ, Sewankambo N, et al. Viral load and heterosexual transmission of human immunodeficiency virus type 1. Rakai Project Study Group. N Engl J Med. 2000;342:921-929.
3. Tovanabutra S, Robison V, Wongtrakul J, et al. Male viral load and heterosexual transmission of HIV-1 subtype E in northern Thailand. J Acquir Immune Defic Syndr. 2002;29:275-283.
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