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

Abstract

Background Few prospective studies of SARS-CoV-2 transmission within households have been reported from the United States, where COVID-19 cases are the highest in the world and the pandemic has had disproportionate impact on communities of color. Methods and Findings This is a prospective observational study. Between April-October 2020, the UNC CO-HOST study enrolled 102 COVID-positive persons and 213 of their household members across the Piedmont region of North Carolina, including 45% who identified as Hispanic/Latinx or non-white. Households were enrolled a median of 6 days from onset of symptoms in the index case. Secondary cases within the household were detected either by PCR of a nasopharyngeal (NP) swab on study day 1 and weekly nasal swabs (days 7, 14, 21) thereafter, or based on seroconversion by day 28. After excluding household contacts exposed at the same time as the index case, the secondary attack rate (SAR) among susceptible household contacts was 60% (106/176, 95% CI 53%-67%). The majority of secondary cases were already infected at study enrollment (73/106), while 33 were observed during study follow-up. Despite the potential for continuous exposure and sequential transmission over time, 93% (84/90, 95% CI 86%-97%) of PCR-positive secondary cases were detected within 14 days of symptom onset in the index case, while 83% were detected within 10 days. Index cases with high NP viral load (>10^6 viral copies/ul) at enrollment were more likely to transmit virus to household contacts during the study (OR 4.9, 95% CI 1.3-18 p=0.02). Furthermore, NP viral load was correlated within families (ICC=0.44, 95% CI 0.26-0.60), meaning persons in the same household were more likely to have similar viral loads, suggesting an inoculum effect. High household living density was associated with a higher risk of secondary household transmission (OR 5.8, 95% CI 1.3-55) for households with >3 persons occupying <6 rooms (SAR=91%, 95% CI 71-98%). Index cases who self-identified as Hispanic/Latinx or non-white were more likely to experience a high living density and transmit virus to a household member, translating into an SAR in minority households of 70%, versus 52% in white households (p=0.05). Conclusions SARS-CoV-2 transmits early and often among household members. Risk for spread and subsequent disease is elevated in high-inoculum households with limited living space. Very high infection rates due to household crowding likely contribute to the increased incidence of SARS-CoV-2 infection and morbidity observed among racial and ethnic minorities in the US. Quarantine for 14 days from symptom onset of the first case in the household is appropriate to prevent onward transmission from the household. Ultimately, primary prevention through equitable distribution of effective vaccines is of paramount importance.

Factors Associated With Household Transmission of SARS-CoV-2

“…Compared with the SAR for 28 studies 12,14,17,27,94 from January to February 2020 (13.4%; 95% CI, 10.7%-16.7%), the SAR was significantly higher for 30 studies 6,7,15,16,19,22,25,26,28,30,[68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86]93 from March to April 2020 (19.4%; 95% CI, 15.2%-24.5%; P = .03) and 15 studies 5,8,10,18,20,21,23,24,29,31,32,35,37,38,40 from July 2020 to March 2021 (31.1%; 95% CI, 22.6%-41.1%; P < .001) but not significantly different from the SAR for 14 studies…”

“…To elucidate factors associated with differences in SAR, we explored attributes of studies from the periods with the lowest and highest household SARs. Among 28 studies 12,14,17,27,94 from January to February 2020 and 15 studies 5,8,10,18,20,21,23,24,29,31,32,35,37,38,40 from July 2020 to March 2021, 6 studies 12,46,54,57,59,62 (21.4%) and 4 studies 8,10,20,23 (25.0%), respectively, reported testing contacts at least twice, 1 study 46 (3.6%) and 3 studies 5,8,23 (18.8%) reported following contacts for longer than 14 days, 1 study 45 (3.6%) and 6 studies 8,23,24,29,37,40 (33.3%) were published as preprints, 21 studies 12,14,27,46,[48][49][50]…”

“…The estimated overall household SAR for all 87 studies was 18.9% (95% CI, 16.2%-22.0%), with significant heterogeneity ( I 2 = 99.4%; P < .001) ( Figure 2 ). Excluding studies with only asymptomatic 85 or pediatric 36 , 66 index cases, studies that tested only 7 , 9 , 15 , 17 , 19 , 24 , 26 , 29 , 30 , 31 , 35 , 37 , 45 , 47 , 61 , 65 , 68 , 69 , 71 , 77 , 79 , 81 , 82 , 86 , 87 , 90 , 92 , 94 or asymptomatic 78 contacts, studies with long follow-up periods (≥21 days), 5 , 8 , 9 , 23 , 46 , 92 and studies published as preprints, 8 , 23 , 24 , 29 , 45 , 79 , 88 , 89 , 90 , 92 the overall SAR among the 47 remaining studies 4 , 6 , 10 , 11 , 12 , 13 , 14 , …”

“…To elucidate factors associated with differences in SAR, we explored attributes of studies from the periods with the lowest and highest household SARs. Among 28 studies 12 , 14 , 17 , 27 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 94 from January to February 2020 and 15 studies 5 , 8 , 10 , 18 , 20 , 21 , 23 , 24 , 29 , 31 , 32 , 35 , 37 , 38 , 40 from July 2020 to March 2021, 6 studies 12 , 46 , 54 , 57 , 59 , 62 (21.4%) and 4 studies 8 , 10 , 20 , 23 (25.0%), respectively, reported testing contacts at least twice, 1 study 46 (3.6%) and 3 studies 5 , 8 , 23 (18.8%) reported following ...…”

Flavonoids are promising safe therapy against COVID-19

“…Recently, several vaccine platforms were entered into the clinical evaluation (Le et al 2020 ). These include (i) Nucleic acid vaccines as mRNA-based-vaccines such as Moderna (Mahase 2020 ), BioNTech/Pfizer (Müller et al 2021 ), CureVac/ Bayer (Rosales-Mendoza et al 2020 ), and Inovio as DNA-based vaccines (Calina et al 2020 ); (ii) Viral vector vaccines as Ad vector (ChAdOx1) developed by AstraZeneca (Wise 2021 ), Johnson – Johnson vaccine developed by Janssen Vaccines (Livingston et al 2021 ) and Sputnik V (Jones and Roy 2021 ) developed by Gamaleya Research Institute of Epidemiology and Microbiology; (iii) Inactivated virus as Sinovac vaccine (Palacios et al 2020 ) developed by China Sinovac biotech company; (iv) Antigen-based vaccine EpiVacCorona that was developed by the Vector Institute (Ryzhikov et al 2021 ). On the other hand, the treatments suggested for COVID-19 are limited to those either still in clinical trials such as favipiravir (Pilkington et al 2020 ), ribavirin (Khalili et al 2020 ), lopinavir-ritonavir (Dalerba et al 2020 ), emetine (Choy et al 2020 ), hydroxychloroquine (Chen et al 2020a ), methionine (Zhang et al 2020 ), homoharringtonine and ivermectin (Elgazzar et al 2020 ) or initially approved by U.S. FDA such as remdesivir (Beigel et al 2020 ).…”