High household transmission of SARS-CoV-2 in the United States: living density, viral load, and disproportionate impact on communities of color.

Understanding the secondary attack rate and the timing of transmission of SARS-CoV-2 within households is important to determine the role of household transmission in the larger pandemic and to guide public health policies about quarantine.Prospective studies looking at the determinants of household transmission are sparse, particularly studies including substantial racial and ethnic minorities in the United States and studies with adequate follow-up to detect sequential transmission events.Identifying individuals at high risk of transmitting and acquiring SARS-CoV-2 will inform strategies for reducing transmission in the household, or reducing disease in those exposed. Between April-November 2020, the UNC CO-HOST study enrolled 102 households across the Piedmont region of North Carolina, including 45% with an index case who identified as racial or ethnic minorities.Overall secondary attack rate was 60% with two-thirds of cases already infected at study enrollment.Despite the potential for sequential transmission in the household, the majority of secondary cases were detected within 10 days of symptom onset of the index case.Viral loads were correlated within families, suggesting an inoculum effect.High viral load in the index case was associated with a greater likelihood of household transmission.Spouses/partners of the COVID-positive index case and household members with obesity were at higher risk of becoming infected.High household living density contributed to an increased risk of household transmission.Racial/ethnic minorities had an increased risk of acquiring SARS-CoV-2 in their households in comparison to members of the majority (white) racial group. Household transmission often occurs quickly after a household member is infected.High viral load increases the risk of transmission.High viral load cases cluster within households - suggesting high viral inoculum in the index case may put the whole household at risk for more severe disease.Increased household density may promote transmission within racial and ethnic minority households.Early at-home point-of-care testing, and ultimately vaccination, is necessary to effectively decrease household transmission.