@CDCMMWR Vital Signs report: The impacts of undiagnosed and delayed diagnosis of #HIV

Friday, December 1, 2017

An MMWR "Vital Signs" early release on undiagnosed HIV infection and its impact on the epidemiology of the epidemic has been making the rounds this week. The report uses data from the National HIV Surveillance System through 2015 to calculate an estimate for the annual number of HIV infections, both diagnosed and undiagnosed:
The first CD4 test after HIV diagnosis and a CD4 depletion model indicating disease progression were used to estimate year of infection and the distribution of time from HIV infection to diagnosis among persons with diagnosed infection. The distribution of diagnosis delay was used to estimate the annual number of HIV infections, which includes persons with diagnosed infection and persons with undiagnosed infection.
The number of persons with undiagnosed HIV infection was estimated by subtracting the number of reported cumulative diagnoses from the number of estimated cumulative infections. The percentage of undiagnosed infections was determined by dividing the number of undiagnosed infections by the total HIV prevalence.
I found the bit about the "CD4 depletion model" to be particularly interesting. This refers to calculating the length of an individual's infection based on their CD4 level at diagnosis by using biomedical data on how quickly HIV kills off CD4 cells. (Most HIV surveillance data comes from lab reports, so surveillance programs receive CD4 and viral load information automatically when the lab report is received.) They can then "backtrack" and compare those estimates with the number of cases that were actually reported for a given year, which allows them to estimate the overall prevalence of HIV and the percentage of those cases that are undiagnosed. The math is relatively simple, but it underscores the importance of supporting disease surveillance systems, as the data they collect can clarify so much of the picture of the overall epidemic.

The article also looks at data on groups at high risk for HIV infection from the National HIV Behavioral Surveillance System, a survey program which collects data from MSM, PWID, and heterosexuals at high risk. Those numbers show that testing has increased among all three groups, but that there were missed opportunities that could be addressed through more widespread routine screening in healthcare settings:
Among persons interviewed through NHBS, the percentage reporting an HIV test in the 12 months preceding the interview increased over time among MSM (from 63% in 2008 to 71% in 2014), persons who inject drugs (from 50% in 2009 to 58% in 2015), and heterosexual persons at increased risk for infection (from 34% in 2010 to 41% in 2016).
In each risk group, at least two thirds of persons who did not have an HIV test had seen a health care provider in the past year (Table 2). Among those who had not tested in the past year and had visited a health care provider, approximately three quarters reported not having been offered an HIV test at any of their health care visits.
Unfortunately, it's tough for me to get excited about progress like this because this kind of national data is always two years delayed. The Obama administration made it a priority to reduce the number of HIV infections, so the importance of HIV prevention programs was taken as a given. It remains to be seen whether this progress will be sustained under the current political climate, particularly in the light of the raging opioid epidemic. Unfortunately, we won't know for another two years.

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