Piero Poletti1, Marcello Tirani2,3, Danilo Cereda2, Filippo Trentini1, Giorgio Guzzetta1, Giuliana Sabatino2, Valentina Marziano1, Ambra Castrofino4, Francesca Grosso4, Gabriele Del Castillo4, Raffaella Piccarreta5,6,7, Aida Andreassi2, Alessia Melegaro5,7,8, Maria Gramegna2, Marco Ajelli9,10, Stefano Merler1. 1. Fondazione Bruno Kessler, Povo, Trento, Italy. 2. Directorate General for Health, Lombardy Region, Milan, Italy. 3. Health Protection Agency of Pavia, Pavia, Italy. 4. Department of Biomedical Sciences for Health, University of Milan, Milan, Italy. 5. Dondena Centre for Research on Social Dynamics and Public Policy, Bocconi University, Milan, Italy. 6. Department of Decision Sciences, Bocconi University, Milan, Italy. 7. CovidCrisisLab, Bocconi University, Milan, Italy. 8. Department of Social and Political Sciences, Bocconi University, Milan, Italy. 9. Department of Epidemiology and Biostatistics, Indiana University School of Public Health, Bloomington. 10. Laboratory for the Modeling of Biological and Socio-technical Systems, Northeastern University, Boston, Massachusetts.
Abstract
Importance: Solid estimates of the risk of developing symptoms and of progressing to critical disease in individuals infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are key to interpreting coronavirus disease 2019 (COVID-19) dynamics, identifying the settings and the segments of the population where transmission is more likely to remain undetected, and defining effective control strategies. Objective: To estimate the association of age with the likelihood of developing symptoms and the association of age with the likelihood of progressing to critical illness after SARS-CoV-2 infection. Design, Setting, and Participants: This cohort study analyzed quarantined case contacts, identified between February 20 and April 16, 2020, in the Lombardy region of Italy. Contacts were monitored daily for symptoms and tested for SARS-CoV-2 infection, by either real-time reverse transcriptase-polymerase chain reaction using nasopharyngeal swabs or retrospectively via IgG serological assays. Close contacts of individuals with laboratory-confirmed COVID-19 were selected as those belonging to clusters (ie, groups of contacts associated with an index case) where all individuals were followed up for symptoms and tested for SARS-CoV-2 infection. Data were analyzed from February to June 2020. Exposure: Close contact with individuals with confirmed COVID-19 cases as identified by contact tracing operations. Main Outcomes and Measures: Age-specific estimates of the risk of developing respiratory symptoms or fever greater than or equal to 37.5 °C and of experiencing critical disease (defined as requiring intensive care or resulting in death) in SARS-CoV-2-infected case contacts. Results: In total, 5484 case contacts (median [interquartile range] age, 50 [30-61] years; 3086 female contacts [56.3%]) were analyzed, 2824 of whom (51.5%) tested positive for SARS-CoV-2 (median [interquartile range] age, 53 [34-64] years; 1604 female contacts [56.8%]). The proportion of infected persons who developed symptoms ranged from 18.1% (95% CI, 13.9%-22.9%) among participants younger than 20 years to 64.6% (95% CI, 56.6%-72.0%) for those aged 80 years or older. Most infected contacts (1948 of 2824 individuals [69.0%]) did not develop respiratory symptoms or fever greater than or equal to 37.5 °C. Only 26.1% (95% CI, 24.1%-28.2%) of infected individuals younger than 60 years developed respiratory symptoms or fever greater than or equal to 37.5 °C; among infected participants older than 60 years, 6.6% (95% CI, 5.1%-8.3%) developed critical disease. Female patients were 52.7% (95% CI, 24.4%-70.7%) less likely than male patients to develop critical disease after SARS-CoV-2 infection. Conclusions and Relevance: In this Italian cohort study of close contacts of patients with confirmed SARS-CoV-2 infection, more than one-half of individuals tested positive for the virus. However, most infected individuals did not develop respiratory symptoms or fever. The low proportion of children and young adults who developed symptoms highlights the possible challenges in readily identifying SARS-CoV-2 infections.
Importance: Solid estimates of the risk of developing symptoms and of progressing to critical disease in individuals infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are key to interpreting coronavirus disease 2019 (COVID-19) dynamics, identifying the settings and the segments of the population where transmission is more likely to remain undetected, and defining effective control strategies. Objective: To estimate the association of age with the likelihood of developing symptoms and the association of age with the likelihood of progressing to critical illness after SARS-CoV-2 infection. Design, Setting, and Participants: This cohort study analyzed quarantined case contacts, identified between February 20 and April 16, 2020, in the Lombardy region of Italy. Contacts were monitored daily for symptoms and tested for SARS-CoV-2 infection, by either real-time reverse transcriptase-polymerase chain reaction using nasopharyngeal swabs or retrospectively via IgG serological assays. Close contacts of individuals with laboratory-confirmed COVID-19 were selected as those belonging to clusters (ie, groups of contacts associated with an index case) where all individuals were followed up for symptoms and tested for SARS-CoV-2 infection. Data were analyzed from February to June 2020. Exposure: Close contact with individuals with confirmed COVID-19 cases as identified by contact tracing operations. Main Outcomes and Measures: Age-specific estimates of the risk of developing respiratory symptoms or fever greater than or equal to 37.5 °C and of experiencing critical disease (defined as requiring intensive care or resulting in death) in SARS-CoV-2-infected case contacts. Results: In total, 5484 case contacts (median [interquartile range] age, 50 [30-61] years; 3086 female contacts [56.3%]) were analyzed, 2824 of whom (51.5%) tested positive for SARS-CoV-2 (median [interquartile range] age, 53 [34-64] years; 1604 female contacts [56.8%]). The proportion of infectedpersons who developed symptoms ranged from 18.1% (95% CI, 13.9%-22.9%) among participants younger than 20 years to 64.6% (95% CI, 56.6%-72.0%) for those aged 80 years or older. Most infected contacts (1948 of 2824 individuals [69.0%]) did not develop respiratory symptoms or fever greater than or equal to 37.5 °C. Only 26.1% (95% CI, 24.1%-28.2%) of infected individuals younger than 60 years developed respiratory symptoms or fever greater than or equal to 37.5 °C; among infectedparticipants older than 60 years, 6.6% (95% CI, 5.1%-8.3%) developed critical disease. Female patients were 52.7% (95% CI, 24.4%-70.7%) less likely than male patients to develop critical disease after SARS-CoV-2 infection. Conclusions and Relevance: In this Italian cohort study of close contacts of patients with confirmed SARS-CoV-2 infection, more than one-half of individuals tested positive for the virus. However, most infected individuals did not develop respiratory symptoms or fever. The low proportion of children and young adults who developed symptoms highlights the possible challenges in readily identifying SARS-CoV-2 infections.
Authors: Gabriella Imbriano; Emmett M Larsen; Daniel M Mackin; Akaisha Kaixuan An; Christian C Luhmann; Aprajita Mohanty; Jingwen Jin Journal: Front Public Health Date: 2021-03-29
Authors: Kristen K Bjorkman; Tassa K Saldi; Erika Lasda; Leisha Conners Bauer; Jennifer Kovarik; Patrick K Gonzales; Morgan R Fink; Kimngan L Tat; Cole R Hager; Jack C Davis; Christopher D Ozeroff; Gloria R Brisson; Daniel B Larremore; Leslie A Leinwand; Matthew B McQueen; Roy Parker Journal: J Infect Dis Date: 2021-10-28 Impact factor: 5.226