The Best of Both Worlds: Collaborations Can Improve Epidemiological Analyses of Public Health Data.

The HIV care continuum has gained significant traction as a useful framework among both public health practitioners and academic researchers. The continuum estimates the proportion of HIV-infected persons who are HIV diagnosed, linked to and retained in care, initiated on antiretroviral therapy, and virally suppressed. Public health practitioners are increasingly being called upon (and required) to estimate and improve the HIV care continuum in their jurisdiction (e.g., state, dependent area, and metropolitan statistical area). Public health estimates of the HIV care continuum typically rely on CD4 counts and viral loads reported to HIV surveillance. In this issue of Sexually Transmitted Diseases, Toren et al. use surveillance data to show that the time between HIV diagnosis and viral suppression for persons diagnosed as having HIV in Seattle & King County decreased dramatically from 2007 to 2013. We welcome the contribution by Toren et al. as a valuable and timely contribution to the literature on the effects of rapidly changing treatment paradigms on improvements in the HIV care continuum. Being population-based, public health surveillance data offer a unique opportunity to obtain unbiased estimates of the HIV care continuum. Estimation of the HIV care continuum is inherently limited in clinical cohorts. Namely, clinical cohorts represent a nonrandom subset of all HIV-diagnosed persons who (1) ever entered care and (2) remained in care at the clinic where the cohort is based. Because surveillance data are population-based, the recent work by Toren et al. has the advantage of being able to include all persons diagnosed as having HIV in Seattle & King County, including persons who never enter care and never achieve viral suppression. The inclusion of persons diagnosed as having HIV avoids bias inherent in clinic-based analyses: (1) of absolute time toviral suppression if personswho never enter care and thus never suppress are excluded from the risk set, (2) of characteristics associated with prompt viral suppression if HIV-infected persons who enter care differ from those who do not enter care, and (3) of changing time to viral suppression over calendar time if the characteristics of HIV-infected persons who entered care varied over time. Most clinics do not have the resources for extensive patient tracing if patients fail to return for follow-up. Patients may leave a clinic because they move out of the area, switch clinical providers within the same area, or fall out of clinical care; this information is not generally recorded. In one clinical cohort, loss to clinic was substantial (5-year risk, 46%), yet mortality among persons lost to clinic was similar to mortality among persons retained in care, suggesting that some of those who were lost to clinic likely entered care elsewhere and loss to clinic may overestimate loss to care. Because public health surveillance data are not clinic based, they (hypothetically) capture laboratory measures for HIV-infected patients, regardless of the provider who ordered the laboratories, and therefore follow patients if they change clinics within the same area. (Rules for laboratory reporting and levels of compliance with reporting rules vary across jurisdictions.) However, public health surveillance data still cannot typically distinguish between persons who move out of jurisdiction and persons who are lost to care. Seattle & King County is one of very few public health agencies that have gathered additional information to distinguish out-migration from loss to care so that emigrants can be censored. Indeed, Seattle & King County is also one of a minority of public health jurisdictions that have been collecting laboratory surveillance data consistently enough to be able to estimate changes in time to viral suppression. Name-based reporting of HIV diagnoses was not implemented in all 50 states until 2008, a full year after follow-up in the analysis by Toren et al. began. From 2011 to 2013, of 50 states and 6 dependent areas, only 19, 18, and 28 jurisdictions (respectively) had laboratory data that were estimated to be at least 95% complete. These observations serve to illustrate both how quickly HIV