Transmission dynamics of COVID-19 in household and community settings in the United Kingdom

Abstract

Background: Households appear to be the highest risk setting for transmission of COVID-19. Large household transmission studies were reported in the early stages of the pandemic in Asia with secondary attack rates ranging from 5-30% but few large scale household transmission studies have been conducted outside of Asia. Methods: A prospective case ascertained study design based on the World Health Organization FFX protocol was undertaken in the UK following the detection of the first case in late January 2020. Household contacts of cases were followed using enhanced surveillance forms to establish whether they developed symptoms of COVID-19, became confirmed cases and their outcomes. Household secondary attack rates and serial intervals were estimated. Individual and household basic reproduction numbers were also estimated. The incubation period was estimated using known point source exposures that resulted in secondary cases. Results: A total of 233 households with two or more people were included with a total of 472 contacts. The overall household SAR was 37% (95% CI 31-43%) with a mean serial interval of 4.67 days, an R0 of 1.85 and a household reproduction number of 2.33. We find lower secondary attack rates in larger households. SARs were highest when the primary case was a child. We estimate a mean incubation period of around 4.5 days. Conclusions: High rates of household transmission of COVID-19 were found in the UK emphasising the need for preventative measures in this setting. Careful monitoring of schools reopening is needed to monitor transmission from children.

Household Transmission of SARS-CoV-2

“…In 5 studies, 20,36,39,48,49 individuals older than 60 years were most susceptible to SARS-CoV-2 infection. Contact age was not associated with susceptibility in 9 studies, 26,28,32,44,47,58,66,67,70 although these were typically less powered to detect a difference. Figure 3 summarizes 15 studies 22,26,29,37,39,42,44,45,47,49,55,59,60,63,65 The second most examined factor was sex of exposed contacts, which was not associated with susceptibility for most studies 20,22,26,32,36,39,44,45,[47][48][49]58,[65][66][67]70 except 3.…”

Characteristics associated with household transmission of SARS-CoV-2 in Ontario, Canada

“…Existing individual-level observational studies of household transmission typically included household contacts identified through contact tracing. [4][5][6][8][9][10] These studies have estimated secondary attack rates among household contacts to be five to ten times as high as in non-household settings. 4,6 Most of these studies were conducted in Asia, included smaller numbers of households, and/or did not compare to households where no secondary transmission occurred.…”

The potential impact of a recent measles epidemic on COVID-19 in Samoa

“…It is also now clear based on viral shedding data that children play an important role in transmission [33], and may even have a higher viral load in the respiratory tract than adults [37]. A household contact study found that COVID-19 attack rates in families were higher when the primary case was a child [40].…”

“…Studies showed children under 5 years have a higher viral load in the respiratory tract than adults or older children [37][38][39]. Another study showed that COVID-19 attack rates in families were higher when the primary case was a child [40]. In the United States, 9.8% of all cases of COVID-19 were children [41].…”