Close Contacts Of COVID-19 Cases Research Articles

Opportunities and lessons learned from a retrospective analysis of administrative billing data to understand the language profile of high-risk close contacts of COVID-19 cases in Ontario.

During a public health emergency, it is vital to have access to data sources that can identify communities disproportionately affected and to ensure public health communications are meeting the needs of diverse populations. To explore how administrative billing data for language interpretation services could be used as an additional source of information to understand the language profile of high-risk close contacts of COVID-19 cases. A retrospective descriptive analysis was conducted using administrative billing data from Public Health Ontario's Contact Tracing Initiative from May 2020 to February 2022. Data from the Contact Tracing Initiative were utilized to identify drivers that could have influenced patterns in language interpretation requests. Trends were compared with community language profiles using 2021 Canadian Census data. Interpreters responded to 2,604 requests across 38,518 interpretation minutes and provided information in 50 different languages. The top five requested languages were French, Arabic, Spanish, Punjabi and Mandarin. Five distinct periods were identified of different language predominance including Spanish in spring/summer 2020, French in summer/fall 2020 and Arabic in spring 2021. Overall, these trends aligned with the language profile of health units contributing most submissions. Public health agencies could benefit from using existing secondary data sources to understand the language interpretation needs of their communities. This study also demonstrated how existing data sources could be used to help assess how communities are being disproportionately affected by public health emergencies and how this might change over time.

The district operation centres in one of the largest local health authorities in Italy to manage COVID-19 surveillance and homecare: first implementation and results of a survey addressed to general practitioners

BackgroundCOVID-19 pandemic represented a shock for healthcare systems. Italy was one of the first country to deal with a huge number of patients to be diagnosed, isolated, and treated with scarce evidence-based guidelines and resources. Several organizational and structural changes were needed to face the pandemic at local level. The article aims at studying the perceived impact of the newly implemented District Operation Centres (DOCs) of Local Health Authority (LHA) Roma 1 in managing active surveillance and home care of COVID-19 patients and their close contacts in cooperation with general practitioners (GPs).MethodsA questionnaire, developed according to Delphi methodology, was validated by 7 experts and administered to a randomized sample of GPs and family paediatricians (FPs). All medical doctors selected received a phone interview between December 2020 and January 2021. The questionnaire investigated general characteristics of the sample, relations with DOC and its usefulness, and potential developments. A descriptive analysis was performed and inferential statistical tests were used to assess differences.ResultsIn April 2020 the LHA Roma 1 implemented one DOCs in each local health district. 215 medical doctors were interviewed, reaching the sample target for health districts (80% CL and 10% MOE) and the whole LHA (90% CL and 5% MOE). Several aspects in the management of COVID-19 cases and close contacts of COVID-19 cases, and of the support of DOCs to GPs/FPs were investigated. More than 55% of the GPs and FPs interviewed found the DOCs useful and more than 78% would recommend a service DOC-like to other LHAs. The medical professionals interviewed would use DOCs in the future as support in treating vulnerable patients, utilizing digital health tools, enlisting specialist doctors, establishing networks, and facilitating professional counselling by nurses.ConclusionsThis study is an attempt to evaluate an organizational change happened during COVID-19 pandemic. DOCs were created to support GPs and FPs as a link between primary healthcare and public health. Although several difficulties were disclosed, DOCs’ experience can help to overcome the fragmentation of the systems and the duality between primary care and public health and make the system more resilient.

Lessons learned from implementing a surge capacity support program for COVID-19 contact management in Ontario

SettingIn Ontario, local public health units (PHUs) are responsible for leading case investigations, contact tracing, and follow-up. The workforce capacity and operational requirements needed to maintain this public health strategy during the COVID-19 pandemic were unprecedented.InterventionPublic Health Ontario’s Contact Tracing Initiative (CTI) was established to provide a centralized workforce. This program was unique in leveraging existing human resources from federal and provincial government agencies and its targeted focus on initial and follow-up phone calls to high-risk close contacts of COVID-19 cases. By setting criteria for submissions to the program, standardizing scripts, and simplifying the data management process, the CTI was able to support a high volume of calls.OutcomesDuring its 23 months of operation, the CTI was used by 33 of the 34 PHUs and supported over a million calls to high-risk close contacts. This initiative was able to meet its objectives while adapting to the changing dynamics of the pandemic and the implementation of a new COVID-19 provincial information system. Core strengths of the CTI were timeliness, volume, and efficient use of resources. The CTI was found to be useful for school exposures, providing support when public health measures were lifted, and in supporting PHU’s reallocation of resources during the vaccine roll-out.ImplicationsWhen considering future use of this model, it is important to take note of the program strengths and limitations to ensure alignment with future needs for surge capacity support. Lessons learned from this initiative could provide practice-relevant knowledge for surge capacity planning.

Utilizing student-led contact tracing initiative to alleviate COVID-19 disease burden in central Pennsylvania

Contact tracing elicits probable contacts from COVID-19 cases. Our student-led contact tracing initiative promoted isolation of both confirmed and probable cases and quarantine of contacts to reduce disease in Central Pennsylvania. Close contacts of COVID-19 cases were contacted by tracers, advised to quarantine, and monitored for 14 days for symptoms. Symptomatic contacts were classified as probable cases and advised to isolate. Data was collected from March 24, 2020 to May 26, 2020. Poisson regression and linear regression were utilized to examine the relationships between case and number of contacts and proportion of symptomatic contacts. Study sample comprised of 346 confirmed and 157 probable cases. Our results indicate a significant difference in percent of household contacts who became symptomatic between confirmed and probable cases (22% vs. 3%; adjusted P<.01). Similarly, probable cases had significantly fewer non-household contacts compared to confirmed cases (0.87 vs. 0.55; adjusted P<.01). Timely notification of exposure to a COVID-19 positive individual by student contact tracers allowed for probable cases to quarantine early in the disease process. Our data suggests that early quarantine and/or isolation may have directly contributed to probable cases having fewer non-household contacts and a smaller proportion of symptomatic household-contacts compared to confirmed cases.

Differences in Transmission between SARS-CoV-2 Alpha (B.1.1.7) and Delta (B.1.617.2) Variants.

ABSTRACTThe present study aimed to compare the susceptibility and infectivity between the Alpha and Delta variants of SARS-CoV-2 and to investigate characteristics of the index case and the contact that may affect transmission. The risk of SARS-CoV-2 infection was compared between close contacts of COVID-19 cases with Alpha and Delta variants during June 2021 to August 2021. In index cases, Spike gene target failure (TaqPath) was used as a proxy of Alpha variant and the L452R mutation (TaqMan) for Delta variant. Cox regression models were used to estimate adjusted relative risks (RR). We compared close contacts of index cases with Alpha (n = 2139) and Delta variants (n = 5439). Delta variant was more transmissible overall (relative risk [RR] 1.32, 95% CI = 1.13 to 1.53), and in non-household contacts (RR 1.71, 95% CI = 1.35 to 2.16), but not in household contacts (RR 1.10, 95% CI = 0.91 to 1.34; Pinteraction < 0.001). Delta variant excess transmission was observed when the index cases were 12 to 39 years old (RR 1.51, 95% CI = 1.27 to 1.79) and the close contacts were 18 to 39 years old (RR 1.62, 95% CI = 1.29 to 2.03), but not among those younger or older than such ages. Differences in transmissibility between variants disappeared with vaccination of the index case (RR 0.68, 95% CI = 0.46 to 1.02), but not with vaccination of the close contact. This report shows that the Delta variant is more transmissible than Alpha variant mainly among young adults. Vaccination of the index cases reduced the excess transmission, which reinforces the recommendation of vaccination to reduce transmission of the Delta variant.IMPORTANCE The higher transmissibility of the Delta variant of SARS-CoV-2 in comparison with the Alpha variant has been reported. We compared the transmission of the Alpha and Delta variants by characteristics and COVID-19 vaccination status of index cases and their close contacts. Interestingly, the Delta variant showed increased transmissibility when the index case was an adolescent or young adult and when the close contact was a young adult; however, in index cases and close contacts of other age groups, transmission did not differ between variants. This may explain the increased proportion of young people who have been infected in the surges due to the Delta variant. The Delta variant was more transmissible than the Alpha variant when the index cases were unvaccinated against COVID-19, and their vaccination equaled the transmissibility of both variants, which suggests a higher impact of vaccination in controlling transmission of the Delta variant.

Preliminary Research on a COVID-19 Test Strategy to Guide Quarantine Interval in University Students

Following COVID-19 exposure, the Centers for Disease Control (CDC) recommends a 10–14-day quarantine for asymptomatic individuals and more recently a 7-day quarantine with a negative PCR test. A university-based prospective cohort study to determine if early polymerase chain reaction (PCR) negativity predicts day 14 negativity was performed. A total of 741 asymptomatic students in quarantine was screened and 101 enrolled. Nasopharyngeal swabs were tested on days 3 or 4, 5, 7, 10, and 14, and the proportion of concordant negative results for each day versus day 14 with a two-sided 95% exact binomial confidence interval was determined. Rates of concordant negative test results were as follows: day 5 vs. day 14 = 45/50 (90%, 95% CI: 78–97%); day 7 vs. day 14 = 47/52 (90%, 95% CI: 79–97%); day 10 vs. day 14 = 48/53 (91%, 95% CI:79–97%), with no evidence of different negative rates between earlier days and day 14 by McNemar’s test, p &gt; 0.05. Overall, 14 of 90 (16%, 95% CI: 9–25%) tested positive while in quarantine, with seven initial positive tests on day 3 or 4, 5 on day 5, 2 on day 7, and none on day 10 or 14. Based on concordance rates between day 7 and 14, we anticipate that 90% (range: 79–97%) of individuals who are negative on day 7 will remain negative on day 14, providing the first direct evidence that exposed asymptomatic students ages 18–44 years in a university setting are at low risk if released from quarantine at 7 days if they have a negative PCR test prior to release. In addition, the 16% positive rate supports the ongoing need to quarantine close contacts of COVID-19 cases.

Covid-19 nelle cure primarie pediatriche in Italia

Introduction: Very few studies have been published on the clinical history and contagiousness of not hospitalized Covid-19 pediatric patients. Therefore, to get deeper in this topic, between October 2020 and March 2021, we carried out an observational study in the pediatric primary care setting in Italy. Methods: The study enrolled patients with Covid-19 disease (cases); patients with suspicious symptoms but negative swab; close contacts of Covid-19 cases. The follow-up was 28 days for patients with Covid-19 disease, 14 days for the other subjects enrolled. Results: 1947 patients aged 0-13 were enrolled: 465 with Covid-19 disease; 549 with suspicious symptoms but negative swab; 933 close contacts of Covid-19 cases. 130 subjects with Covid-19 were asymptomatic at the time of diagnosis. Among the others, in children aged 0-2 the most frequent symptom was rhinitis (41%) followed by fever (38%) and cough (31%). In children aged 3-13 the most frequent symptom was headache (30%) followed by rhinitis (23%), asthenia (18%), fever (16%), cough (11%). No symptoms alone were sufficient to induce or rule out the suspicion of the Covid-19 disease diagnosis. A multiple logistic regression analysis, conducted for the purpose, allowed to build a score capable of inducing disease suspicion in patients older than 2 years of age, based on: fever, rash, rhinitis, headache and asthenia. Conclusions: This study compared subjects with SARS-CoV-2 infection with unaffected subjects with similar symptoms and confirmed that it is impossible to clinically distinguish Covid-19 from other similar respiratory diseases in pediatric age. The obtained score, potentially useful and valid during the study period, could not be applied in other epidemiological scenarios.

Efectividad de la vacuna BNT162b2 para prevenir la COVID-19 en personal sanitario

ObjectiveTo assess the effectiveness of the vaccine against SARS-CoV-2 (BNT162b2) in healthcare personnel of a health department. MethodTest-negative case̶control study. Healthcare personnel with suspected COVID-19 and healthcare personnel close contacts of COVID-19 cases were included between January 27th and June 6th, 2021. They were PCR tested for SARS-CoV-2; those with positive PCR were considered cases and those with negative PCR were considered controls. The adjusted vaccine effectiveness (aVE) to prevent COVID-19 cases and their 95% confidence interval (95%CI) were calculated using the formula VE=(1−odds ratio)×100. Results624 healthcare personnel were included, of which 43 (6.9%) were considered cases and 581 (93.8%) controls. The aVE of the complete regimen was 96.3% (95%CI: 82.5̶99.2). The aVE of the incomplete pattern was 68.0% (95%CI: 30.0̶85.4). ConclusionsThe administration of the complete pattern of BNT162b2 vaccine against SARS-CoV-2 is effective for the prevention of cases of COVID-19 in healthcare personnel.

Epidemiological characteristics of close contacts of COVID-19 cases and infection-related risk factors in Beijing

Objective: To analyze the epidemiological characteristics of close contacts of COVID-19 cases and infection-related risk factors in Beijing and provide evidences for COVID-19 prevention and control. Methods: A total of 20 681 close contacts of COVID-19 cases, who had exposures during January 6, 2020 to February 15, 2021, were traced in Beijing. The information about their demographic characteristics, exposure history, and quarantine outcomes were collected and analyzed with descriptive statistics. The logistic regression analysis was used to identify the risk factors for COVID-19. Results: The infection rate SARS-CoV-2 in close contacts was 2.16% (447/20 681). The age M(P25, P75) was 35 (27, 49) years. The majority of the close contacts were aged 20-59 years, accounting for 81.77% (16 912/20 681). Centralized isolation was the major type of medical observation, accounting for 82.15% (16 989/20 681). Among the exposure types, working and studying in the same room (16.06%, 3 322/20 681), sharing same transport vehicle (12.88%, 2 664/20 681), performing diagnosis and treatment nursing (7.80%,1 612/20 681), and living together (7.23%,1 495/20 681), accounting for 43.96% (9 093/20 681). The index cases included staff (19.34%, 3 999/20 681), the unemployed (17.34%, 3 586/20 681), people engaged in business service (13.85%, 2 864/20 681), people engaged in food service (10.77%, 2 228/20 681), their close contacts accounted for 61.30% (12 677/20 681). Multivariate logistic regression analysis showed that compared with other types of exposure, the risk factors for infection were having meal together (OR=3.96, 95%CI: 2.30-6.83) and living together (OR=6.41, 95%CI:4.48-9.17); Compared with the other occupations, the index case being engaged in food service (OR=3.06, 95%CI:1.29-7.25) and teacher (OR=4.94, 95%CI:1.43-17.08) were risk factors for the infection. Conclusions: The main environmental exposure types of SARS-CoV-2 infection in close contacts were having meal together and living together. Contact with the index case being engaged in food service and teacher increased the risk for COVID-19. Comprehensive prevention and control measures such as centralized isolation and vaccination should be continued.

Sensitivity and specificity of nucleic acid testing in close contacts of COVID-19 cases in Guangzhou

Objective: To analyze the sensitivity and specificity of SARS-CoV-2 nucleic acid testing in 20 348 close contacts of COVID-19 cases in different prevention and control stages in Guangzhou and to provide scientific evidence for optimizing epidemic response strategies. Methods: A total of 20 348 close contacts of COVID-19 cases in Guangzhou were traced between February 21 and September 22,2020. All the close contacts were tested for the nucleic acid of SARS-CoV-2. The sensitivity and specificity of nucleic acid testing and diagnosis in the different prevention and control stages were compared. Results: In 20 348 close contacts, 12 462 were males (61.24%), the median (P25,P75) of age of them was 31.0 years (23.0,43.0), the median number (P25,P75) of nucleic acid testing for them was 2.0 (1.0,3.0), and the median (P25,P75) of their quarantine days was 12.0 (8.0,13.0) days, respectively. A total of 256 COVID-19 cases were confirmed in the close contacts after seven nucleic acid tests. In the 1st, 2nd, 3rd and 7th nucleic acid testing, the sensitivity and specificity were 69.14% and 99.99% (177 cases confirmed), 89.84% and 99.99% (230 cases confirmed), 97.27% and 99.99% (249 cases confirmed), and 100.00% and 99.98%, respectively. In the three stages of COVID-19 prevention and control in China: domestic case stage, imported case stage, and imported case associated local epidemic stage, the sensitivity of the 1st nucleic acid testing was 70.68%, 68.00% and 67.35%, and the specificity was 99.98%, 100.00% and 100.00%, respectively. Conclusions: The sensitivity of nucleic acid testing in the close contacts at the different stages were consistent with slight decrease, which might be related to the increased proportion of asymptomatic infections in the late stage of epidemic prevention and control with COVID-19 in Guangzhou. It is suggested to give three nucleic acid tests to improve the sensitivity and reduce false negative risk.

Asymptomatic COVID-19 in South Africa - implications for the control of transmission.

Asymptomatic COVID-19 may contribute significantly to the pandemic trajectory based on global biological, epidemiological and modelling evidence. A retrospective analysis was done to determine the proportion of asymptomatic COVID-19 in the workplace during the lockdown period from 27 March to 31 May 2020. We found that nearly 45% of cases were asymptomatic at the time of the first test. This high proportion of asymptomatic COVID-19 cases has implications for interventions, such as enforcing quarantine of all close contacts of COVID-19 cases regardless of symptoms.

Contact tracing of staff in the emergency department during the COVID-19 pandemic.

Contact tracing of staff in the emergency department during the COVID-19 pandemic.

Risk Factors, Epidemiological and Clinical Outcome of Close Contacts of COVID-19 Cases in a Tertiary Hospital in Southern India

Introduction: The knowledge of epidemiologic characteristics and transmission dynamics of a novel pathogen, such as Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) among close contacts can help in planning and development of effective control policies in different parts of the world. Aim: To assess the epidemiological and clinical outcome of close contacts of Coronavirus Disease (COVID-2019) cases admitted in a tertiary COVID hospital and to assess the role of risk factors in predicting the epidemiological outcome of these contacts. Materials and Methods: The current retrospective cohort study was conducted among 1286 close contacts of COVID-19 patients admitted to Government Medical College, Thrissur, Kerala. The data collection was done by a semi-structured telephonic interview by the contact tracing team. The questions included the type of exposure to the index case, symptoms if any, date of last exposure with COVID-19 positive patients, and final COVID-19 status of the contact at the end of 14 days. The association of risk factors of COVID-19 positivity was done using binary logistic regression. Results: Proportion of close contacts of COVID-19 who developed the disease was 24.2% (21.87-26.52%). The mean incubation period was found to be 4.22 days (C.I-3.71-4.65). The serial interval mean was found to be 5.24 days (C.I 4.764-5.716). The proportion of household contacts of COVID-19 cases who developed the disease was found to be 26% (C.I-23%-29%). The majority (52.4%) of infections among contacts were asymptomatic. Most common symptom among the COVID-19 positive was fever (32.8%) followed by cough (16.1%). The most common risk factors of infection among primary close contacts were sharing the same room (adjusted odds ratio-2.394) and common use of fomites (adjusted odds ratio-1.953) while use of a mask was found to be protective (adjusted odds ratio-0.570). Significant factors associated with the type of contact with infection were workplace-related contact (adjusted odds ratio-6.629), household contact (adjusted odds ratio-4.856), and travel-related contact (adjusted odds ratio-2.899). Conclusion:The study concludes important risk factors of transmission among close contacts of COVID-19 as being in a household, workplace and travel related contact where the use of mask was found to be protective. The study also concludes that most of the COVID-19 infections in close contacts are asymptomatic.

Analysis on medical observation of 1 665 close contacts of COVID-19 cases

Objective: To understand the identification and medical observation of close contacts of COVID-19 cases in a city and provide scientific basis for the adjustment of the epidemic prevention and control strategies. Methods: Descriptive epidemiological methods were used to analyze the general characteristics of all the close contacts of COVID-19 cases in a city. Throat swabs were collected from the close contacts for real-time fluorescent RT-PCR. The confirmed cases were diagnosed according to diagnosis and treatment of COVID-19 (trial version 5). Results: Among the 1 665 close contacts of COVID-19 cases in a city, 10 were diagnosed as COVID-19 cases during the medical observation period, accounting for 30.30% of all the confirmed cases in a city, most of them were close relatives of the confirmed cases. The longest contact time with the confirmed cases was 8 days and the shortest was 0 days. Ten COVID-19 cases in close contacts constituted to six family clusters. Conclusions: In COVID-19 prevention and control in a city, the active tracking of the transmission chains of the confirmed cases and timely identification of the close contacts were conducted. The people who had close contacts with the confirmed COVID-19 cases within 14 days before onset were all placed under medical observation, which played a key role in the effective prevention and control of COVID-19 epidemic in a city. Nearly one third of COVID-19 cases occurred during the medical observation period, so the infection sources were effectively controlled and transmission routes were effectively blocked, which greatly facilitated the prevention of the clusters of COVID-19 cases.

Investigation of transmission chain of a cluster COVID-19 cases

Objective: To analyze of the transmission characteristics of a cluster of COVID-19 cases in Chongqing and evaluate the infectivity of COVID-19 in the incubation period. Methods: A retrospective survey was conducted by using unified questionnaire through field and telephone interviews among 129 close contacts of COVID-19 cases. The relationship of transmission was indicated by transmission chain, and the infectivity was analyzed by the contact history. Results: This cluster of COVID-19 cases occurred after a classmate party involving members in three families and work fellows in a factory (R(0)=3.8). The infection rate during the incubation period was 17.57%. On average, it was infectious three days before onset. There was significant difference in infection rate among different contact modes (χ(2)=15.10, P<0.01), There was significant difference in infection rate among single exposureswith different time length (χ(2)=25.08, P<0.01). Conclusions: COVID-19 is highly infectious in the incubation period. The more confined the space is, the higher the risk is,and the longer the single exposure is, the higher the risk of transmission is. Indirect contact transmission still exists.

Epidemiological characteristics of infection in COVID-19 close contacts in Ningbo city

Objective: To estimate the infection rate of close contacts of COVID-19 cases, and to evaluate the risk of COVID-19 under different exposure conditions. Methods: A prospective study was used to conduct continuous quarantine medical observations of close contacts of people infected with COVID-19, collect epidemiological, clinical manifestations, and laboratory test data to estimate the infection rate of close contacts under different exposures. Results: The epidemiological curve of COVID-19 in Ningbo showed persistent human-to-human characteristics. A total of 2 147 close contacts were tracked and investigated. The total infection rate was 6.15%. The infection rates of confirmed cases and positive contacts were 6.30% and 4.11%, respectively. The difference was not statistically significant (P>0.05). Among close contacts of different relationships, friends/pilgrims (22.31%), family members (18.01%), and relatives (4.73%) have a higher infection rate, and close contacts of medical staff were not infected. Differences in infection rates among the close contacts were statistically significant (P<0.005). Living with the case (13.26%), taking the same transportation (11.91%), and dining together (7.18%) are high risk factors for infection. Cross-infection in the hospital should not be ignored (1.94%). The median of incubation period is 5 days. Conclusion: The infection rate of close contacts of COVID-19 cases is high, and isolation medical observation measures should be implemented in strict accordance with the close contact management plan.

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

Background: Understanding community-based SARS-CoV-2 transmission is crucial to inform public health decisions. 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.Findings: Overall, 219 COVID-19 index 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 the semi-confinement, compared to none (aOR 0·35, 95%CI 0·16-0·74). The individual risk of household members to be seropositive was lower in large households (22% less per each additional person).Interpretation: We find that, 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 specific protective measures applicable at home. For elderly couples, who were especially at risk, providing them external support for daily basic activities is essential.Funding: Center for Primary Care and Public Health (Unisanté), Canton of Vaud, Leenaards Foundation, Fondation pour l'Université de Lausanne. SerocoViD is part of Corona Immunitas coordinated by SSPH+.Declaration of Interests: We declare no competing interests.Ethics Approval Statement: The Cantonal Ethics Committee of Vaud, Switzerland (ID 2020-00887) approved the protocol.

Guidelines for Investigation and Management of Close Contacts of COVID-19 Cases

Guidelines for Investigation and Management of Close Contacts of COVID-19 Cases