As of the end of July 2020, more than 17 million cases of coronavirus disease (COVID-19) had been reported globally with more than 660,000 deaths. The causative agent, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is primarily transmitted through the droplet route although aerosol, contact and faecal transmission may also contribute.
Investigations of household transmission dynamics were reported early in the pandemic in China and other countries in Asia. Households appeared to be the highest risk setting for transmission with reported symptomatic secondary attack rates (SAR) in household contacts ranging from 5% to 30%. Rates of symptomatic infection increase with age and risk factors for more severe disease include age, male sex and a range of comorbidities. As countries move from broad physical distancing measures to more targeted approaches, a detailed understanding of risk factors for transmission is increasingly important.
In the United Kingdom (UK), the first cases of COVID-19 were reported in late January 2020, the number of cases rapidly increased from March before plateauing, then declining after physical distancing measures were introduced. We followed up the first few hundred (FF100) cases of COVID-19 in the UK and their household contacts using the World Health Organization (WHO) 'first few X cases and contacts' (FFX) protocol that was established before the COVID-19 pandemic. We have previously reported on the characteristics and outcomes of these cases. Here we describe the transmission dynamics and risk factors for transmission and acquisition of symptomatic infection.
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Bernal, J., Panagiotopoulos, N., Byers, C., Vilaplana, T., Boddington, N., Zhang, X., Charlett, A., Elgohari, S., Coughlan, L., Whillock, R., Logan, S., Bolt, H., Sinnathamby, M., Letley, L., MacDonald, P., Vivancos, R., Edeghere, O., Anderson, C., Paranthaman, K., Cottrell, S., McMenamin, J., Zambon, M., Dabrera, G., Ramsay, M. & Saliba, V. 2022, 'Transmission dynamics of COVID-19 in household and community settings in the United Kingdom, January to March 2020', Eurosurveillance, 27(15). https://doi.org/10.2807/1560-7917.ES.2022.27.15.2001551