SARS-CoV-2 contact tracing among disadvantaged populations during epidemic intervals should be a priority strategy: results from a pilot experiment in Barcelona

Vallès, Xavier; Roure, Sílvia; Valerio, Lluís; López-Muñoz, Israel; Pérez-Quílez, Olga; Soldevila, Laura; Martín-Cano, Laura; Estrada, Oriol; Palacín, Maria Dolors; Blanco, Ignacio; Orozco, Jaime; Esquerrà , Anna; Villanova, Xavier

Objectives The aim of this study was to trace contacts of COVID-19 hospitalised patients and determine the risk factors of infection in urban areas. Study design Longitudinal analysis of contacts identified from index cases. Methods A contact tracing study was carried out in the Northern Metropolitan area of Barcelona, Spain, during the inter-epidemic lapse of May to July 2020, a period of low SARS-CoV-2 incidence. Index cases were notified from the referral hospital. Contacts were traced and followed-up for 14 days. Reverse transcription polymerase chain reaction (RT-PCR) was performed at day 0 and day 14 for contacts. Results In total, 368 contacts were identified from 81 index cases (median of 7 contacts per index case), from which 308 were traced successfully. The median age of contacts was of 28 years old, 62% (223 of 368) were males and 28 were non-nationals (34.1%). During the follow-up period, 100 contacts tested positive for COVID-19 (32.5% [95% confidence interval {CI} = 27.3–38.0]), with a secondary infection rate of 48.3% (95% CI = 40.8–55.9) among housemates. Clusters of index and respective contacts tended to aggregate within disadvantaged neighbourhoods (p < 0.001), and non-national index cases resulted in higher secondary infection rates compared with nationals (51.0% [95% CI = 41.0–60.9] vs 22.3% [95% CI = 16.8–28.8]; p < 0.001). Conclusions Disadvantaged communities experience a disproportionate burden of COVID-19 and may act as infection reservoirs. Contact tracing with a cross-cutting approach among these communities is required, especially during inter-epidemic periods.