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Age and Likelihood of Symptoms and Critical Disease After SARS-CoV-2
Quick Takes
- This cohort study of close contacts of patients with SARS-CoV-2 infection reports that most SARS-CoV-2–infected individuals did not develop respiratory symptoms or fever.
- Since asymptomatic infections can be missed by surveillance systems, they can reduce the effectiveness of the test, trace, and isolate strategies in keeping SARS-CoV-2 transmission under control.
- These findings may be particularly germane to schools as children have a low risk of developing fever or respiratory symptoms, but are capable of transmitting infection, thus possibly becoming a source of silent SARS-CoV-2 transmission.
Study Questions:
What is the association of age with the likelihood of developing symptoms and the likelihood of progressing to critical illness after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection?
Methods:
The investigators conducted a cohort study that 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 coronavirus disease 2019 (COVID-19) were selected as those belonging to clusters (i.e., 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. The main outcomes measures were age-specific estimates of the risk of developing respiratory symptoms or fever ≥37.5 °C (99.5 °F) and of experiencing critical disease (defined as requiring intensive care or resulting in death) in SARS-CoV-2–infected case contacts.
Results:
In total, 5,484 case contacts (median [interquartile range] age, 50 [30-61] years; 3,086 female contacts [56.3%]) were analyzed, 2,824 (51.5%) of whom tested positive for SARS-CoV-2 (median [interquartile range] age, 53 [34-64] years; 1,604 female contacts [56.8%]). The proportion of infected persons who developed symptoms ranged from 18.1% (95% confidence interval [CI], 13.9%-22.9%) among participants <20 years to 64.6% (95% CI, 56.6%-72.0%) for those aged ≥80 years. Most infected contacts (1,948 of 2,824 individuals [69.0%]) did not develop respiratory symptoms or fever ≥37.5 °C. Only 26.1% (95% CI, 24.1%-28.2%) of infected individuals <60 years developed respiratory symptoms or fever ≥37.5 °C; among infected participants >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:
The authors concluded that among close contacts of patients with confirmed SARS-CoV-2 infection, more than one-half of individuals tested positive for the virus but most infected individuals did not develop respiratory symptoms or fever.
Perspective:
This cohort study of Italian close contacts of patients with confirmed SARS-CoV-2 infection reports that most SARS-CoV-2–infected individuals did not develop respiratory symptoms or fever of 37.5 °C or higher, highlighting the challenges of controlling COVID-19 outbreaks with individual-level interventions. Since asymptomatic infections can be missed by surveillance systems, they can reduce the effectiveness of the test, trace, and isolate strategies in keeping SARS-CoV-2 transmission under control. These findings may be particularly germane to understanding SARS-CoV-2 transmission patterns in schools, as children have a low risk of developing fever or respiratory symptoms, but are capable of transmitting infection, thus possibly becoming a source of silent SARS-CoV-2 transmission.
Clinical Topics: COVID-19 Hub, Geriatric Cardiology, Prevention
Keywords: Asymptomatic Infections, Coronavirus, COVID-19, Critical Care, Critical Illness, Disease Outbreaks, Geriatrics, Immunoglobulin G, Primary Prevention, Quarantine, Reverse Transcriptase Polymerase Chain Reaction, SARS-CoV-2, Schools
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