COVID-19 (SARS-CoV-2) Outbreaks in Rural United Kingdom: Patterns of Spread and Empirical Evidence for the 'Rule of Six'

Background: Multiple countries across the world are facing the second wave of severe acute respiratory syndrome coronavirus. Understanding the early transmission dynamics is crucial for outbreak control measures and evaluating public health policy. Methods: We used detailed contact tracing data for the rural county of Lincolnshire to quantify risk factors of infection and model disease spread. We used subcritical branching processes ( <1) to capture the stochastic nature of local transmission dynamics in Tier 2. Negative binomial model was used for the branching processes and also the for statistical regression models to calculate the Incident Rate Ratios (IRRs). Findings: 158,390 individuals were contact traced between the periods of May 11, 2020 to September 14, 2020 during the early phase of the second wave with 1143 confirmed positives in Lincolnshire. We found empirical evidence in support of the “rule of 6” for secondary contacts and largest gathering component size of 60 people. There is highly-over dispersed offspring distribution k=0·35 95% CI [0·41-0·29] indicative of super spreading events. We found through multivariable analysis, evidence of young adult population driving the outbreak and protection increasing with age for those in isolation. There is an increased risk of 66% (IRR 1·66, 95% CI [1·02 - 2·20]), 50% (IRR 1·50, 95% CI [1·16 - 2·37]) associated with eating out and shopping followed by social events respectively when compared to house hold acquired covid-19 infections. Interpretation: Generating functions and random graph theory help model the local transmission heterogeneities from the very onset of the outbreak. Focusing on the secondary contacts and case cluster size distribution is a better method for detecting the stochastic beginnings of a pandemic, rather than decision-making being based on exceeding particular threshold. Contact tracing and viral testing is essential to provide the reliable data and help with the public health policy for effective interventions. Funding: NoneDeclaration of Interests: None.Ethics Approval Statement: Ethics permission has been granted by University of Lincoln Ethics Committee (Protocol ID: 4188).