Introduction: CDC and state/local health departments analyze HIV sequences to identify molecular clusters representing rapid transmission. Local analyses can be timelier, but are limited to sequences available in the local surveillance system, and thus may miss all or part of clusters spanning multiple jurisdictions. We assessed the added value of national analyses for clusters missed or only partially detected by local analyses. Methods: We reviewed national quarterly analyses of HIV sequences (September 2021 – June 2023) that identified priority clusters (defined as ≥5 diagnoses in the past 12 months within a genetic distance of ≤0.005 substitutions per site among people with HIV diagnosed during the most recent three years). For each cluster, we simulated whether and when single-jurisdiction analysis would meet priority threshold and calculated the proportion of cluster members that could be identified locally. Results: Of 149 clusters detected in the national analysis, 91 (61%) clusters would have been detected concurrently by local analysis, 27 (18%) would have delayed detection (median: 59 days), and 31 (21%) would not have been detected locally. In clusters detected by both approaches, an average of 91% of cluster members identified in the national analysis would have also been identified in the local analysis. Conclusion: National analyses detected clusters that local analyses missed, identified additional cluster members, and found certain clusters earlier. National cluster detection plays a vital role in enhancing local detection activities.
Johnson et al. (Mon,) studied this question.