Onset and window of SARS-CoV-2 infectiousness and temporal correlation with symptom onset: a prospective longitudinal community cohort study
The study “Onset and window of SARS-CoV-2 infectiousness and temporal correlation with symptom onset: a prospective longitudinal community cohort study” offers significant insights into the infectiousness of COVID-19 in a real-world setting.
Here’s a detailed summary:
- Study Background and Objective: Understanding the window of SARS-CoV-2 infectiousness is vital for developing effective public health policies to reduce transmission. This study aimed to characterize infectiousness throughout the entire course of infection in a community setting, particularly focusing on the temporal correlation with symptom onset.
- Study Design and Methodology: The study, conducted by the Assessment of Transmission and Contagiousness of COVID-19 in Contacts (ATACCC), was a UK-based prospective longitudinal community cohort. It involved contacts of newly diagnosed PCR-confirmed SARS-CoV-2 cases, tracking viral RNA load and infectious viral shedding daily across the infection course. Participants, including household and non-household contacts aged 5 years or older, also completed a daily diary to monitor symptom emergence.
- Findings and Implications: Between September 2020 and October 2021, 738 contacts were enrolled, with 173 testing PCR positive. Key findings include:
- The median duration of infectiousness was 5 days.
- Although 63% of cases had PCR-detectable virus before symptom onset, only 20% shed infectious virus presymptomatically.
- Symptom onset typically occurred 3 days before peak viral RNA and peak infectious viral load.
- Notably, 65% of cases continued to shed infectious virus 5 days after symptom onset, and 24% did so after 7 days.
- Lateral flow device (LFD) results correlated poorly with infectious viral shedding during the viral growth phase but showed high sensitivity during the decline phase.
- Study Contributions and Context: This study is the first to serially quantify both viral RNA and infectious culturable virus from the start of natural SARS-CoV-2 infection. It captures the early viral growth phase, crucial for understanding transmission dynamics. The findings suggest that under a 5-day self-isolation period from symptom onset, two-thirds of cases released into the community would still be infectious, albeit with reduced viral shedding. The study’s high-resolution community-based data are pivotal in informing infection control guidance.
- Research Significance: The study’s comprehensive approach provides a more accurate understanding of the infectiousness window in naturally acquired infections. It highlights the variability in infectious viral shedding, reflecting the diverse demographics and transmission routes in community settings. By delineating the infectious period relative to symptom onset and diagnostic test results, the study offers valuable insights for calibrating isolation guidance.
In summary, this study underscores the complexity of COVID-19 infectiousness, providing crucial data to inform public health strategies. It emphasizes the need for a nuanced approach to isolation and testing policies, considering the variability in infectiousness and the effectiveness of different diagnostic tools at various infection stages.