Prevalence of SARS-CoV-2 in Household Members and Other Close Contacts of COVID-19 Cases: A Serologic Study in Canton of Vaud, Switzerland

Abstract

Background Research on SARS-CoV-2 transmission within households and other close settings using serological testing is scarce. Methods We invited COVID-19 cases diagnosed between February 27 and April 1, 2020, in canton of Vaud, Switzerland, to participate, along with household members and other close contacts. Anti-SARS-CoV-2 IgG antibodies were measured using a Luminex immunoassay. We estimated factors associated with serological status using generalized estimating equations. Results Overall, 219 cases, 302 household members, and 69 other close contacts participated between May 4 and June 27, 2020. More than half of household members (57.2%, 95%CI 49.7-64.3) had developed a serologic response to SARS-CoV-2, while 19.0% (95%CI 10.0-33.2) of other close contacts were seropositive. After adjusting for individual and household characteristics, infection risk was higher in household members aged 65 or more than in younger adults (aOR 3.63, 95%CI 1.05-12.60), and in those not strictly adhering to simple hygiene rules like hand washing (aOR 1.80, 95%CI 1.02-3.17). The risk was lower when more than 5 people outside home were met during semi-confinement, compared to none (aOR 0.35, 95%CI 0.16-0.74). Individual risk of household members to be seropositive was lower in large households (22% less per each additional person). Conclusions During semi-confinement, household members of a COVID-19 case were at very high risk of getting infected, 3 times more than close contacts outside home. This highlights the need to provide clear messages on protective measures applicable at home. For elderly couples, who were especially at risk, providing external support for daily basic activities is essential.

Caring During COVID-19: Reconfigurations of Gender and Family Relations During the Pandemic in Switzerland

“…The findings complement qualitatively the quantitative results of the SérocoViD project by shedding light on the reconfigurations of care and gender in the daily navigation of risk and protection, which was not captured by the quantitative approach. They confirm the epidemiological importance of the household (Dupraz et al, 2020) as a key determinant in understanding how families managed viral transmission and protection. But what are the consequences of these observations for the management of the pandemic at national level?…”

“…As epidemiological studies have shown, the domestic space is a privileged site for transmission (Dupraz et al, 2020), putting extra pressure on family members to negotiate risk in their daily lives, especially when several generations share the same space. The literature in early 2020 did not show clearly how care activities, borne mainly by women, and more broadly gender and intergenerational dynamics, affected and intersected with viral exposure and protective measures.…”

Using secondary cases to characterize the severity of an emerging or re-emerging infection

“…For fever (Fig. 1 ), 16/18 studies reported higher frequency for index cases than secondary cases 15 – 17 , 19 – 23 , 26 , 27 , 29 , 31 , 38 , 40 , 41 , 48 , with 11 of them reported significant difference 15 , 17 , 19 , 21 – 23 , 26 , 29 , 38 , 41 , 48 . For cough (Fig.…”

“…On the basis of our selection criteria, 561 of those studies were excluded and 38 met our inclusion criteria 15 – 52 (Table S1 ). Of these, 19 studies provided information on types of symptoms 15 – 23 , 26 – 29 , 31 , 38 , 40 , 41 , 44 , 48 , 10 studies provided information on case severity 15 , 18 , 23 , 24 , 26 , 29 , 30 , 32 , 35 , 44 , 33 studies provided symptom status 15 , 16 , 18 , 19 , 21 – 26 , 28 – 30 , 32 , 34 – 42 , 44 , 46 – 52 , 10 studies provided hospitalization 30 , 33 , 34 , 36 , 37 , 39 , 43 , 48 , 50 , 51 , and 7 studies provided fatality 27 , 30 , 33 , 37 , 39 , 43 , 45 for both index and secondary cases. Overall, 50,382 index cases and 30,309 secondary cases provided information on at least one measure of clinical severity and type of symptoms.…”

“…For ascertainment methods of index cases, almost all studies used PCR, with seven studies additionally used either symptom 17 , 43 , radiology 17 , 26 , 27 , 33 or serology 21 , 27 , 33 , 46 , while one study did not use PCR and used rapid test 34 . For ascertainment methods of secondary cases, majority studies used PCR, with seven studies additionally used either symptom 17 , 43 , radiology 17 , 26 , 27 , 33 or serology 22 , 27 , 33 , 46 , while three studies used serology 25 , 39 , 48 and one study used rapid test 34 , but not PCR. Regarding to the test coverage among secondary cases, 23 studies tested all identified contacts to detect secondary cases, 2 studies only tested symptomatic persons 20 , 45 , 4 studies tested less than 70% of identified contacts 34 , 40 , 43 , 50 and 5 studies provided no information on test converge 17 , 19 , 21 , 46 , 49 .…”