Cluster randomized trial
When the high-touch program first launched in January 2021, the team members non-randomly targeted a subset of “priority” ZIP Codes (see All Santa Clara County ZIP Codes were considered for our randomized assignment scheme, but because of capacity constraints, we designed the trial to equitably allocate high-touch contact tracing to a feasible subset of ZIP Codes. Each week, we calculated the COVID-19 positivity rate for each ZIP Code. We also received an estimate of the County’s operational capacity for the coming week, and translated that to an approximate number of ZIP Codes that could be assigned to the high-touch team. We then selected twice that number of top ZIP Codes, ranked by both positivity rate and SVI, to be eligible for randomized assignment. Per County objectives, the original 12 “priority” ZIP Codes were always eligible to be randomized, though in practice these were at the top of SVI and typically eligible anyway through the protocol. Of the total eligible ZIP Codes, ranging from 16 to 53 over the course of the trial, half were then randomly assigned by computer algorithm for prioritization by the high-touch team; the other half were routed through the standard protocol, along with ineligible ZIP Codes. Prioritization meant that for each batch of assignments, high-touch contact tracers prioritized contacting cases from assigned ZIP Codes, but because of fluctuating operational conditions which often deviated from our weekly forecasts, not all cases from these ZIP Codes were subject to high-touch contact tracing. If there was extra capacity, high-touch team members were assigned cases from the eligible-but-not-assigned ZIP Codes. For an illustration of the assignment scheme in an example week, as well other exceptions to the assignment scheme that were of de minimis magnitude, see The Santa Clara County Public Health Department and Stanford University, Stanford, California, deemed this work public health surveillance; the Revised Common Rule deems “public health surveillance activities” not subject to IRB oversight or requirements for informed consent under 45 CFR § 46. Thus, it was not submitted for IRB approval, but was subjected to privacy and compliance review by Santa Clara County.