SARS-CoV-2 Contacts’ Symptom Development and Secondary Attack Rate: A Retrospective Analysis of a Contact-Tracing Cohort in Catalonia

• Published in: COVID Vol. 3; no. 4; pp. 428 - 439
• Main Authors: Mallafré-Larrosa, Meritxell, Herrero Garcia, Mercè, Mendoza-Funes, Sergi, Martínez-Solanas, Èrica, Patsi-Bosch, Glòria, Mendioroz Peña, Jacobo, Ciruela Navas, Pilar
• Format: Journal Article
• Language: English
• Published: MDPI AG 01-04-2023
• Subjects: contact tracing; COVID-19; quarantine; SARS-CoV-2; secondary attack rate
• ISSN: 2673-8112; 2673-8112
• DOI: 10.3390/covid3040032

Contact tracing outcome indicators, such as symptom development (SD) and secondary attack rate (SAR) among close contacts (CCs), are key to understanding SARS-CoV-2 transmission. This study analyses SD and SAR and estimates the incubation period (IP) from a cohort of 47,729 CCs from 17,679 SARS-CoV-2 cases diagnosed in Catalonia (Spain) from May to August 2020. Globally, 19.4% of the CCs reported symptoms, especially adult women living in urban areas. SAR was 24.5%, notably higher among infants (37.6%), and 45.9% of secondary cases (SCs) were asymptomatic. Household CCs had 98% (OR: 1.98, 95% CI: 1.81–2.18) and 138% (2.38, 2.19–2.58) increased risk of SD and becoming SCs compared to social settings. The IP was 3.42 days, being 4.10 days among social CCs, and only 15.4% and 4.8% of SCs developed symptoms after days 7 and 10 of quarantine, respectively. These results, notably the higher SAR among asymptomatic children, highlight the importance of diligent monitoring to inform SARS-CoV-2 control strategies.