key: cord-0296636-qde8xvrc
authors: Drolet, M.; Godbout, A.; Mondor, M.; Drolet-Roy, L.; Beraud, G.; Lemmieux-Mellouki, P.; Demers, E.; Boily, M.-C.; Sauvageau, C.; De Serres, G.; Hens, N.; Beutels, P.; Dervaux, B.; Brisson, M.
title: Time trends in social contacts before and during the COVID-19 pandemic: the CONNECT study
date: 2021-10-07
journal: nan
DOI: 10.1101/2021.10.06.21264632
sha: 001fe29d66b837d5230f22d8a9c8617895f13a06
doc_id: 296636
cord_uid: qde8xvrc

ABSTRACT Background: Since the beginning of the Covid-19 pandemic, many countries, including Canada, have adopted unprecedented physical distancing measures such as closure of schools and non-essential businesses, and restrictions on gatherings and household visits. We described time trends in social contacts for the pre-pandemic and pandemic periods in Quebec, Canada. Methods: CONNECT is a population-based study of social contacts conducted shortly before (2018/2019) and during the Covid-19 pandemic (April 2020 to February 2021), using the same methodology for both periods. We recruited participants by random-digit-dialing and collected data by self-administered web-based questionnaires. Questionnaires documented socio-demographic characteristics and social contacts for two assigned days. A contact was defined as a two-way conversation at a distance [≤]2 meters or as a physical contact, irrespective of masking. We used weighted generalized linear models with a Poisson distribution and robust variance (taking possible overdispersion into account) to compare the mean number of social contacts over time by characteristics. Results: A total of 1291 and 5516 Quebecers completed the study before and during the pandemic, respectively. Contacts significantly decreased from a mean of 8 contacts/day prior to the pandemic to 3 contacts/day during the spring 2020 lockdown. Contacts remained lower than the pre-Covid period thereafter (lowest=3 contacts/day during the Christmas 2020/2021 holidays, highest=5 in September 2020). Contacts at work, during leisure activities/other locations, and at home with visitors showed the greatest decreases since the beginning of the pandemic. All sociodemographic subgroups showed significant decreases of contacts since the beginning of the pandemic. Conclusion: Physical distancing measures in Quebec significantly decreased social contacts, which most likely mitigated the spread of Covid-19.

On September 1 st 2021, Canada surpassed 1.5 million confirmed cases of COVID-19, and >25% of these cases were from Quebec (1) . While the province of Quebec was the epicenter of the first wave, most Canadian provinces experienced stronger second and third waves in terms of cases and hospitalisations. Since the beginning of the pandemic, Canada has adopted unprecedented physical distancing measures from complete lockdowns to a combination of school and non-essential businesses closures and restrictions on gatherings and household visits, depending on epidemiological indicators and regions (2) .

Given that physical distancing measures are a cornerstone of public health COVID-19 mitigation efforts, it is important to examine how social contacts changed over time: 1) to better understand the dynamics of the pandemic, 2) to inform future measures, and 3) to provide crucial data for mathematical modeling. To our knowledge, this is the first study that has compared social contacts documented shortly before and during the COVID-19 pandemic using the same methodology.

The main objective of this study is to describe the time trends in social contacts for the COVID-19 prepandemic (2018-2019) and pandemic periods (April 2020-February 2021) in Quebec, Canada using a social contact survey and a representative sample of the population. Specific objectives are to describe the time trends in the number of social contacts, overall and by location (home, work, school, public transport, leisure, other) and by key socio-demographic characteristics. , Table S1 ). All CONNECT phases were conducted with the same methodology.

The target population of CONNECT consisted of all non-institutionalized Quebecers without any age restriction (e.g., elderly living in retirement homes who generally have personal phone lines were . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted October 7, 2021. ; https://doi.org/10.1101/2021. 10 .06.21264632 doi: medRxiv preprint eligible but those living in long-term care home (nursing homes, Quebec CHSLD) were not eligible).

We used random digit dialling to recruit participants. The randomly generated landline and mobile phone number sample was provided by ASDE, a Canadian firm specialized in survey sampling (3) .

After having explained the study, verified eligibility of the household and documented the age and sex of all household members, we randomly selected one person per household to participate in the study, using a probability sample stratified by age. This recruitment procedure was sequentially repeated for every new phase of CONNECT (i.e, new participants were recruited for every CONNECT phase).

We collected data using a self-administered web-based questionnaire. A secured individualized web link to the questionnaire and information about the study were sent by email to each selected participant who consented to participate in the study. Parents of children aged less than 12 years were asked to complete the questionnaire on behalf of their child, whereas teenagers aged 12-17 years completed their own questionnaire, after parental consent.

The same questionnaire was used for all CONNECT phases. The first section of the questionnaire documented key socio-demographic characteristics. The second section was a social contact diary, based on instruments previously used in Polymod and other similar studies(4-6) (an example of the diary is provided in the Appendix, Figure S1 ). Briefly, participants were assigned two random days of the week (one week day and one weekend day) to record every different person they had contact with between 5 am and 5 am the following morning. A contact was defined as either physical (handshake, hug, kiss) or nonphysical (two-way conversation in the physical presence of the person, at a distance equal or less than 2 meters, irrespective of masking). Participants provided the characteristics of the contact persons (age, sex, ethnicity, and relationship to themselves (e.g., household member, friend, colleague)) as well as characteristics of the contacts with this person: location where the contact(s) occurred (home, work, daycare/school, public transport, leisure, other location), duration, usual frequency of contact with that person, and whether the contact was physical or not. Participants reporting more than 20 professional contacts per day were asked not to report all their professional contacts in the diary. Instead they were asked general questions about these professional contacts: age groups of the majority of contact persons, average durations of contacts and whether physical contacts were generally involved or not. Additional questions about teleworking were included from CONNECT2 onwards.

. CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted October 7, 2021. ; https://doi.org/10.1101/2021.10.06.21264632 doi: medRxiv preprint All CONNECT phases were approved by the ethics committee of the CHU de Québec research center (project 2016-2172) and we commissioned the market company Advanis for recruitment and data collection. All participants gave their consent to participate in the study during the recruitment phone call.

We weighted the participants of the CONNECT 1-5 surveys by age, sex, region (Greater Montreal and other Quebec regions), and household composition (households without 0-17-year-olds, households with 0-5-year-olds, if not with 6-14-year-olds, if not with 15-17-year-olds), using the Quebec data of the 2016 Canadian census and we verified that they were representative of the Quebec population for key socio-demographic characteristics. To obtain daily number of social contacts on a weekly basis, we weighted the number of daily contacts reported during the week (5/7) and the weekend (2/7). We classified the type of employment of workers using the 2016 National occupation classification (NOC) (7) .

We estimated the number of social contacts per person and per day, for all locations combined and for 6 different locations: home, work, school, public transportation, leisure, and other locations. To do so, several steps were necessary. First, for a contact person met in more than a single location during a single day, the location of the contact was assigned in the following hierarchical order, according to risk of transmission: home, work, school, public transport, leisure and other locations (8) . For example, if a parent reported contacts with his child at home, in public transportation and in a leisure activity, we only considered the home contact to avoid counting contacts with the same person multiple times.

Second, for workers reporting more than 20 professional contacts per working day, we added their reported number of professional contacts to the work location for their working day(s). Similar to other studies which allowed a maximal number of contacts per day (4, 5, 9) , we truncated professional contacts at a maximum of 40 per day to eliminate extreme values and contacts at low risk of transmission of infectious diseases. Third, we identified all workers in schools through their NOC code and job descriptions and attributed their professional contacts to the school location. We did so to describe social contacts in schools, not only between students, but also between students and their teachers, educators, and other school's workers. Unless specified, we estimated the mean number of contacts in the different locations using a population-based denominator. With this method, all individuals were considered in the denominator of each location had they reported contacts or not for that location. The sum of contacts in the different locations gives the total number of contacts.

. CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted October 7, 2021. ; https://doi.org/10.1101/2021.10.06.21264632 doi: medRxiv preprint Using data available from CONNECT1-5, we determined different periods to reflect the Quebec Covid-19 epidemiology, their related physical distancing measures, and expected seasonality in social contacts (Appendix Figure S2 ). We used data collected from February 1 st 2018 to March 17 th 2019 as our pre-Covid period. We used data collected from April 21 st to May 25 th 2020 to represent the first wave, data collected from July 3 rd to August 31 st 2020 to represent the summer, and data collected from September 1 st 2020 to February 26 th 2021 to represent the second wave. We further stratified the second wave to represent periods of expected seasonality in social contacts: September with the return to school and at work, fall with gathering restrictions, the Christmas holidays with school and work vacations and closure of non-essential business, January and February 2021 with the gradual return to work and school after Christmas vacations and school/non-essential business closures, and the introduction of a curfew.

We compared the mean number of social contacts over time (total or by location) using weighted generalized linear models with a Poisson distribution and an identity link. Generalized estimating equations with robust variance (10) were used to account for the correlation between the two days of diary data collection and overdispersion. We also compared the mean number of social contacts according to different key socio-demographic characteristics using the same procedure and adjusting for age. Results are presented as the absolute difference in the mean number of contacts compared to the previous period or between subgroups.

All statistical analyses were performed with SAS version 9.4.

A total of 1291, 546, and 4970 Quebecers completed the social contact questionnaires during the pre-Covid period (CONNECT1), the first wave (CONNECT2), and summer 2020 and second wave (CONNECT3-5), respectively. Participation rates (number of questionnaires completed among consenting participant) were 30%, 38%, and 34% for CONNECT 1,2, and 3-5 respectively (Appendix Figure S3 ). These participants were generally representative of the Quebec general population, and they were comparable across the different phases of CONNECT (Table 1) .

During the pre-pandemic period, the mean number of social contacts per person per day was 7.8 (95% confidence interval (CI):7.2-8.5) (Figure 1 and Appendix Table S2 ). This number decreased . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted October 7, 2021. ; https://doi.org/10.1101/2021.10.06.21264632 doi: medRxiv preprint significantly by 60% during the spring 2020 lockdown to 3.1 (95% CI:2.6-3.5). It then increased gradually during summer 2020 and peaked at 5.0 (95% CI:4.3-5.8) contacts/day in September; this peak coincided with the return to school and work. The mean number of contacts decreased significantly again during fall 2020 to 4.1 (95% CI:3.7-4.5) when physical distancing measures were intensified in Quebec to control the second wave. The mean number of social contacts also decreased significantly during the Christmas holidays at 2.9 (95% CI:2.7-3.1) because of school and work vacations and closure of non-essential businesses. There was a trend towards increasing numbers of contacts in January (3.5, 95% CI (3.0-3.9)) with the gradual return to school and in February 2021 (4.0, 95% CI (3.3-4.6)) with the re-opening of non-essential businesses.

During the pre-pandemic period, the great majority of contacts occurred at home (2. Contacts in the other locations (transport, leisure and other) represented a small proportion of overall contacts during the pre-pandemic period (1.3 contacts). They also decreased significantly since the beginning of the pandemic and stayed low through the study period.

The location of social contacts varied substantially by age (Figure 2 , Appendix Table S3 ). Contacts in households represented an important part of contacts for all age groups. Contacts in other locations were highly dependent on age. The main locations of contacts away from home for individuals aged 0-17, 18-65, and >65 years were, respectively, school, work, and other locations.

During the pre-pandemic period, the mean number of social contacts at school/daycare for youth aged 0-17 years was 3.3 contacts (Figure 2A) . These contacts significantly decreased to nearly 0 during the spring 2020 lockdown and the Christmas holidays. They reached the pre-pandemic level with the return to school in September (4.0 contacts), during fall 2020 (3.0) and in February 2021 (3.7). Except for post-secondary, similar time trends in contacts at school/daycare were observed by education level (daycare, elementary, high school) (Appendix Table S4 ).

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The copyright holder for this preprint this version posted October 7, 2021. ; https://doi.org/10.1101/2021.10.06.21264632 doi: medRxiv preprint During the pre-pandemic period, the mean number of contacts at work for adults aged 18-65 years was 5.6 ( Figure 2B ). These contacts significantly decreased to 1.7 during the spring 2020 lockdown and thereafter remained significantly lower than the pre-pandemic period (from 1.3 during the Christmas holidays to 2.7 in September). The number of contacts at work varied by the type of occupation and the proportion of workers reporting teleworking, and therefore having no contact at work (Appendix Tables S5,S6) During the pre-pandemic period, the mean number of social contacts in other locations for adults older than 65 years was 1.6 ( Figure 2C ). These contacts decreased significantly at the beginning of the pandemic and remained low through the study period (between 0.2 and 0.8). Therefore, adults older than 65 years had virtually no contact outside their house during this period.

During the pre-pandemic period, the mean number of social contacts was significantly higher among individuals living in households with ≥3 individuals (vs households with 1-2 individuals), in households with 0-17-year-olds (vs household without 0-17-year-olds), among native French or English speakers (vs other mother tongues), and among individuals with a university degree (vs no degree) (Figure 3 , Appendix Table S3 ). During the first wave, social contacts significantly decreased for most socio-demographic characteristics. The mean number of social contacts slightly increased after the first wave for all socio-demographic characteristics, although it remained lower than the prepandemic period through the study period. During the second wave, the only significant differences between socio-demographic characteristics were a higher number of contacts in households with more individuals and/or households with 0-17-year-olds, mainly explained by the greater number of contacts with household members. Of note, individuals with a university degree had the greatest decrease of their social contacts during the first wave (from 10.7 to 2.5, p<0.0001) and their contacts remained relatively low through the study period (2.5 to 4.4).

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The copyright holder for this preprint this version posted October 7, 2021. ; https://doi.org/10.1101/2021.10.06.21264632 doi: medRxiv preprint

Public health measures to control the Covid-19 spread in Quebec had a significant impact on the number of social contacts. Contacts decreased from a mean of 8 contacts per day prior to the pandemic to 3 contacts per day during the spring 2020 lockdown, a 60% decline. Contacts then increased gradually during the summer to peak at 5 contacts per day in September with the return to school and at work (36% decline vs pre-Covid). Contacts decreased thereafter during the fall 2020 and winter 2021 to about 4 contacts per day as the physical distancing measures were intensified in Quebec to control the second wave of Covid-19 (47% decline vs pre-Covid). Contacts at work, at school, in leisure activities, and at home with visitors showed the greatest changes through the study period. Before the pandemic, adults aged 18-65 years, individual with a university degree, those living in households with 3 or more individuals and/or in households with 0-17-year-olds, and native French or English speakers reported the greatest number of social contacts. Contacts decreased significantly among all sociodemographic subgroups during the spring 2020 lockdown and remained lower than the pre-pandemic period through the study period.

Our results indicating a 60% reduction of social contacts during the spring 2020 lockdown in Quebec lockdown period (12, (16) (17) (18) (19) and similar increasing trends in social contacts after the first lockdown when physical distancing measures were relaxed (12, 18, 20) . Our results are also consistent with Google phone mobility data for Quebec showing substantial decreases in visits of about 80% in retail & recreation, work, and transit transportation stations during the spring 2020 lockdown compared to . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted October 7, 2021. ; https://doi.org/10.1101/2021.10.06.21264632 doi: medRxiv preprint January 2020. Mobility increased thereafter but remained lower than the pre-Covid levels for these locations (mean decreases of 20%, 25% and 45% for visits in retail & recreation, work, and transit transportation stations, respectively, from September to Mid-December 2020)(21).

To our knowledge this is one of the few population-based studies of social contacts worldwide to compare social contacts during the pandemic to those documented shortly before the pandemic using the same methodology. Only one other study conducted in the Netherland included social contacts documented shortly before the pandemic (in 2016-2017) and during the pandemic using the same methodology (18) . However, CONNECT has some limitations. Firstly, previous data suggested that social contacts measured with survey methodology could underestimate the number of social contacts compared with a sensors methodology, particularly for contacts of short duration(22, 23). More specifically, parents participating in CONNECT reported difficulties in reporting contacts at school on behalf of their child. Secondly, although CONNECT is population-based with a random recruitment of the general population, volunteer participants may differ from those refusing to participate in the study and may be those adhering the most to the public health measures. However, we have collected a wealth of information regarding the participant's characteristics and we are confident that the recruitment process was successful in providing a sample of participants generally representative of the Quebec general population (in terms of region, participation rate to education and employment, race, country of origin and mother tongue), and samples are comparable across the different phases of the study. Thirdly, given that public health measures undertaken aimed at limiting social contacts, social desirability may have contributed to an underestimation of contacts. Some participants may not have reported all their contacts, particularly contacts forbidden by public health measures. These three main limitations would likely bias our results towards an underestimation of social contacts. Nonetheless, changes in social contacts measured in our study closely followed the epidemiology and physical distancing measures in Quebec (Appendix Figure S2 ). For example, the beginning of the second wave coincided with an increasing number of social contacts related to school and work return in September.

The number of cases stabilisation/decrease of the second wave coincided with a decreasing number of contacts related to the intensification of public health measures in January and February 2020. transmission. Our results suggest that Quebecers have been generally adherent to public health . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. In conclusion, physical distancing measures in Quebec were effective at significantly decreasing social contacts, which most likely helped prevent Covid-19 spread and generalized overflow of hospital capacity. It is important to continue monitoring contacts as vaccines are rolled out.

. CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted October 7, 2021. . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted October 7, 2021. ; https://doi.org/10.1101/2021.10.06.21264632 doi: medRxiv preprint . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. 

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