Key Points Question How does SARS-CoV-2 spread within a city, and are there instrumental neighborhoods that might modulate the spread? Findings This epidemiological cohort study of 2646 patients with COVID-19 conducted in the third most populated city in Spain found that the neighborhood where the COVID-19 testing facility was located also had the highest number of total connections (both inbound and outbound). The mean income and population density had a direct correlation with the number of cases. Meaning These findings suggest that a selective and strategic lockdown of specific neighborhoods could help reduce the spread of SARS-CoV-2. This epidemiological cohort study describes the local transmission pattern of SARS-CoV-2 in Valencia, Spain. Importance Limited information on the transmission and dynamics of SARS-CoV-2 at the city scale is available. Objective To describe the local spread of SARS-CoV-2 in Valencia, Spain. Design, Setting, and Participants This single-center epidemiological cohort study of patients with SARS-CoV-2 was performed at University General Hospital in Valencia (population in the hospital catchment area, 364 000), a tertiary hospital. The study included all consecutive patients with COVID-19 isolated at home from the start of the COVID-19 pandemic on February 19 until August 31, 2020. Exposures Cases of SARS-CoV-2 infection confirmed by the presence of IgM antibodies or a positive polymerase chain reaction test result on a nasopharyngeal swab were included. Cases in which patients with negative laboratory results met diagnostic and clinical criteria were also included. Main Outcomes and Measures The primary outcome was the characterization of dissemination patterns and connections among the 20 neighborhoods of Valencia during the outbreak. To recreate the transmission network, the inbound and outbound connections were studied for each region, and the relative risk of infection was estimated. Results In total, 2646 patients were included in the analysis. The mean (SD) age was 45.3 (22.5) years; 1203 (46%) were male and 1442 (54%) were female (data were missing for 1); and the overall mortality was 3.7%. The incidence of SARS-CoV-2 cases was higher in neighborhoods with higher household income (β 2 [for mean income per household] = 0.197; 95% CI, 0.057-0.351) and greater population density (β 1 [inhabitants per km 2 ] = 0.228; 95% CI, 0.085-0.387). Correlations with meteorological variables were not statistically significant. Neighborhood 3, where the hospital and testing facility were located, had the most outbound connections (14). A large residential complex close to the city (neighborhood 20) had the fewest connections (0 outbound and 2 inbound). Five geographically unconnected neighborhoods were of strategic importance in disrupting the transmission network. Conclusions and Relevance This study of local dissemination of SARS-COV-2 revealed nonevident transmission patterns between geographically unconnected areas. The results suggest that tailor-made containment measures could reduce transmission and that hospitals, including testing facilities, play a crucial role in disease transmission. Consequently, the local dynamics of SARS-CoV-2 spread might inform the strategic lockdown of specific neighborhoods to stop the contagion and avoid a citywide lockdown.
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