Table 1. Close contact study characteristics.
| Study ID | Country | Study Design/Setting | Type of
transmission |
Population/environment | Test method | Timing of sample collection | Viral
culture |
Cycle threshold | Other information |
|---|---|---|---|---|---|---|---|---|---|
| Abdulrahman 2020 | Bahrain | Observational comparative
Country-wide 09/2020 |
Community | Before and after study of subjects
attending 2 religious events |
PCR | Not reported | No | >40 was considered
negative |
A 10-day period before the event was compared to a 10-day
period beginning 10 days after the event. All symptomatic individuals and close contacts to a confirmed case were tested. Positive and negative controls were included for quality control purposes. |
| Adamik 2020 | Poland | Observational Home | Household | 9756 index cases; 3553 secondary cases | Not reported | Not reported | No | No | Only cases for which clear epidemiological links were
registered as household transmission together with their source cases were included. Cases in social care units and households of minimum 15 inhabitants were removed from the analysis, as an initial analysis revealed that those were not representative for the overall population, due to over- represented comorbidities and severe cases. |
| Agergaard 2020 | Denmark | Home quarantine with 1
asymptomatic index case 11/03/2020 to 01/04/2020 |
Household | Family cluster of 5: Index case arranged
a self-imposed 2-week home quarantine along with family of four |
PCR
Serology |
Not reported for PCR | No | Not specified for PCR | Index case recently returned from skiing trip in Austria
iFlash SARS-CoV-2 N/S IgM/IgG cut-off: ≥12 AU/ml = positive. DiaSorin SARS-CoV-2 S1/S2 IgG cut-off: ≥15 AU/ml = positive |
| Angulo-Bazán 2020 | Peru | Observational retrospective
Household 23/04/2020 to 02/05/2020 |
Household | 52 households in Metropolitan Lima with
only one member with COVID-19 Contacts cohabited in same home with index case |
RT-PCR (index)
Serology |
Not reported | No | Not specified | Evaluation was conducted 13.6 ± 3.7 days after the diagnostic
test |
| Armann 2020 | Germany | Observational - cross-sectional
Schools, homes May to October 2020 |
Local
Household |
1538 students and 507 teachers were
initially enrolled, and 1334 students and 445 teachers completed both study visits. |
Serology | Week 0 and Week 16 | No | N/A | an index (S/C) of < 1.4 was considered negative whereas
one >/= 1.4 was considered positive) and an ELISA detecting IgG against the S1 domain of the SARS-CoV-2 spike protein (Euroimmun® Anti-SARS CoV-2 ELISA) (a ratio < 0.8 was considered negative, 0.8–1.1 equivocal, > 1.1 positive) |
| Arnedo-Pena 2020 | Spain | Retrospective cohort Homes
February-May 2020 |
Household | 347 index cases: 745 household contacts | RT-PCR | Not reported | No | Not specified | COVID-19 cases of community outbreaks and from institutions
as nursing homes were excluded. Secondary attack rate was defined as the proportion of secondary cases from the total of contacts that live in the household of index case. |
| Baker 2020 | USA | Observational
Acute-care hospital |
Nosocomial | 44 HCWs who provided care for a
hospitalized patient with COVID-19 without PPE due to delayed diagnosis of COVID-19 |
RT-PCR | Not reported | No | Not specified | Contact and droplet precautions (including eye protection)
were instituted |
| Baettig 2020 | Switzerland | Retrospective case series
Military canton March 2020 |
Local | 1 index case; 55 contacts | RT-PCR Serology | PCR: Within 24 hrs of index case
for symptomatic subjects Serology: 14 days post-exposure |
No | Not reported | Positive cases were defined with two positive PCR testing for
SARS-CoV-2 from nasopharyngeal swabs. |
| Bao 2020 | China | Observational Entertainment
venue January and February 2020 |
Community | Potentially exposed workers, customers
and their family members potentially exposed to COVID‐19 subject at a swimming pool |
RT-PCR | Not reported | No | Not specified | Men and women exhibited different usage behaviour in that
male bathers occupied the entire area, but mainly stayed at the lounge hall, while female bathers always went home after a bath. The temperature and humidity were significantly higher than what they would have been in an open air‐conditioning environment. |
| Basso 2020 | Norway | Observational study
Hospital |
Nosocomial | Quarantined HCWs exposed to COVID-19
patient |
PCR
Serology |
Approximately 2 weeks after viral
exposure; 3 weeks for serology |
No | N/A
S/CO ratio ≥1 is positive for antibody |
The HCWs were quarantined for 2 weeks due to participation
in aerosol-generating procedures (AGPs) with insufficient personal protective equipment (PPE), or close contact viral exposure (defined as ≤2 m for ≥15 min). |
| Bays 2020 | USA | Observational study
Community hospital and university medical centre February and March, 2020 |
Nosocomial | Two index patients and 421 exposed HCWs | RT-PCR | Not reported | No | Not specified | Exposed staff were identified by analyzing the EMR and
conducting active case finding in combination with structured interviews. They wore neither surgical masks nor eye protection, and were risk stratified based on examination of the medical record and subsequent phone interviews as follows: high risk: nose or mouth exposed during intubation or bronchoscopy; moderate: nose or mouth exposed and for over 2 minutes; and low: nose or mouth exposed under 2 minutes. Ct was 25 for 1 index case - day 15 |
| Bi 2020 | China | Retrospective cohort
Home or quarantine facility January-February 2020 |
Local
Household Community |
391 SARS-CoV-2 cases and 1286 close
contacts |
RT-PCR | RT-PCR | No | Not reporred | Close contacts were identified through contact tracing of
a confirmed case and were defined as those who lived in the same apartment, shared a meal, travelled, or socially interacted with an index case 2 days before symptom onset. Casual contacts (eg, other clinic patients) and some close contacts (eg, nurses) who wore a mask during exposure were not included in this group. |
| Blaisdell 2020 | USA | Observational study
4 overnight camps June–August 2020 |
Community | Multilayered prevention and mitigation
strategy 642 children and 380 staff members, aged 7–70 years |
RT-PCR | 4.1 to 9.1 days after camp arrival | No | Not specified | Hygiene measures: Precamp quarantine, pre- and postarrival
testing and symptom screening, cohorting, and physical distancing between cohorts. In addition, camps required use of face coverings, enhanced hygiene measures, enhanced cleaning and disinfecting, maximal outdoor programming, and early and rapid identification of infection and isolation. |
| Böhmer 2020 | Germany | Observational
Workplace, home January-February 2020 |
Local
Household |
1 index case; 241 contacts | RT-PCR WGS | 3–5 days post-exposure | No | Not reported | |
| Boscolo-Rizzo 2020 | Italy | Cross-sectional
Homes March to April 2020 |
Household | 179 primary cases; 296 household contacts | RT-PCR | Unclear | No | Not reported | |
| Brown 2020 | USA | Survey - cross-sectional
Classroom February to March, 2020 |
Local | Students exposed to an index case
(teacher) |
Serology | 2 weeks post-exposre to index
case |
No | Reciprocal titers of
>400 considered positive Reciprocal titers of >100 but <400 considered indeterminate |
|
| Burke 2020 | USA | Observational prospective
Homes February to March 2020 |
Household | 10 primary cases; 445 close contacts | Not reported | Within 2 weeks of exposure to
infected case |
No | Not reported | 19 (4%) of the 445 contacts were members of a patient’s
household, and five of these 19 contacts continued to have household exposure to the patient with confirmed COVID- 19 during the patient’s isolation period; 104 (23%) were community members who spent at least 10 minutes within 6 feet of a patient with confirmed disease; 100 (22%) were community members who were exposed** to a patient in a health care setting; and 222 (50%) were health care personnel |
| Canova 2020 | Switzerland | Observational case series
Primary care setting |
Nosocomial | 1 index case; 21 HCWs who interacted with
index case without PPE |
RT-PCR | 7 days after the initial exposure | No | Not reporred | |
| Cariani 2020 | Italy | Retrospective
Hospital March to April 2020 |
Nosocomial | HCWs in close contact with SARS-CoV-2-
positive cases (patients, co-workers, or relatives), or with symptoms of RTI |
RT-PCR | Not reported | No | <40 considered
positive |
|
| Charlotte 2020 | France | Retrospective
Indoor choir rehearsal March 2020 |
Community | Nonventilated room; sitting less close to
one another than usual, but at a distance of <1.82m |
RT-PCR | Not reported | No | Not reported | |
| Chaw 2020 | Brunei | Observational
Various March 2020 |
Local
Community |
Primary cases: Presumably infected at
religious event in Malaysia Secondary cases: Epidemiologic link to a primary case |
RT-PCR | Not reported | No | Not reported | Household, workplace, social, and a local religious gathering.
Initial cluster of SARS-CoV-2 cases arose from 19 persons who had attended the Tablighi Jama’at gathering in Malaysia, resulting in 52 locally transmitted cases. |
| Chen 2020 | China | Aircraft
24 January 2020 |
Aircraft | Close contact to 2 passengers presenting
with a fever and URTI symptoms |
RT-PCR | Not reported | No | Not reported | The aircraft was equipped with air handling systems. |
| Chen 2020a | China | Retrospective observational
Home or workplace January-March 2020 |
Local
Household |
69 recurrent-positive patients; 209 close
contacts |
RT-PCR | Every 3 days | No | Not specified | |
| Chen 2020b | China | Prospective cohort
Hospital January-February 2020 |
Nosocomial | 5 index patients; 105 HCWs | RT-PCR
Serology |
From 14 days post-exposure: 1st
& 14th day of quarantine |
No | <40 considered
positive |
|
| Chen 2020c | China | Observational
Various January to March 2020 |
Local
Household Community Nosocomial |
157 locally reported confirmed cases,
30 asymptomatic infections; 2147 close contacts |
Not reported | Unclear | No | Not reported | Family members, relatives, friends/pilgrims, colleagues/
classmates, medical staff, and general personnel judged by the investigator. |
| Cheng 2020 | Taiwan | Observational
Homes, hospital January to March 2020 |
Household
Nosocomial |
100 confirmed cases of confirmed; 2761
close contacts |
RT-PCR | Unclear | No | Not reported | |
| Chu 2020 | USA | Observational
Various January 2020 |
Community | Close contacts for an early confirmed case
of COVID-19 |
RT-PCR
Serology |
Unclear | No | Antibody titers
>400 considered seropositive. |
Office, Community, Urgent care clinic identified via contact
tracing |
| Chu 2020a | USA | Retrospective cohort study
Household |
Household | Household contacts of primary cases
defined as children and adolescents with lab-confirmed COVID-19 (n=224) |
Not reported | Not reported | No | Not reported | Did not distinguish between confirmed and probable cases
among household contacts. A “primary case” is camp attendee with the earliest onset date in the household and a “secondary case” as a household contact with confirmed or probable COVID-19. |
| Contejean 2020 | France | Observational Comparative
Tertiary-care university hospital Feb-Mar 2020 |
Nosocomial | HCW exposed to COVID-19 patients | RT-PCR | Not reported | No | Not reported:
result was +ve if 3/5 of gene targets amplified |
Hygiene measures: All employees were encouraged to wear
a face mask as often as possible in hospital (particularly in the presence of other persons), to wash/disinfect their hands regularly (and after every contact with other persons), to stay at least 2 meters away from others, to cover their mouth and nose with a tissue or sleeve when coughing or sneezing, to put used tissues in the bin immediately and wash hands afterwards, to avoid touching eyes, mouth. Educational messages were released on the internal website and on posters placed in all hospital premises. |
| COVID-19 National Emergency Response Center 2020 | S. Korea | Observational
Various January to March 2020 |
Local
Household Nosocomial |
30 cases; 2,370 contacts | RT-PCR | Not reported | No | Not reported | Homes, work, hospitals |
| Danis 2020 | France | Observational case series
Chalet, school January to February 2020 |
Local
Household |
I adult case with 15 contacts in chalet; 1
paediatric case with 172 school contacts |
RT-PCR | Within 5 days of diagnosis of
cases |
No | Not reported | The index case stayed 4 days in the chalet with 10 English
tourists and a family of 5 French residents. One pediatric case, with picornavirus and influenza A coinfection, visited 3 different schools while symptomatic. |
| Dattner 2020 | Israel | Observational
Home March to June 2020 |
Household | 637 households, average household size of
5.3 |
RT-PCR
Serology |
Serology: 4 weeks post PCR
testing |
No | Not reported | |
| de Brito 2020 | Brazil | Observational descriptive
Household April-May 2020 |
Household | Socially distanced household contacts of
index case |
RT-PCR
Serology |
Serology: 4 weeks post-exposure
PCR unclear |
No | Not reported | Index case: First member of the cluster who had symptoms
and who had a known risk of exposure outside the household during the family's stay in the same condominium; secondary case: Contacts with the index case. Asymptomatic patients: Those who had household contact and positive serology but no symptoms. Probable cases corresponded to confirmed case contacts who developed symptoms compatible with COVID despite negative serology and/or negative RT-PCR results. |
| Deng 2020 | China | Observational
Home January to February 2020 |
Household | 27 cases; 347 close contacts | Not reported | Not reported | No | Not reported | |
| Desmet 2020 | Belgium | Observational - cross-sectional
School November 2019 to March 2020 |
Local | 84 aged between 6 and 30 months
attending daycare |
RT-PCR | First weeks of the epidemic in
Belgium |
No | Not reported | |
| Dimcheff 2020 | USA | Survey: cross-sectional
Tertiary-care referral facility June 8 to July 8, 2020 |
Community
Nosocomial Household |
HCW exposed to COVID-19 patients either
in or outside hospital |
Serology | 8 weeks post-exposure | No | Not reported | Hygiene measures: Daily COVID-19 symptom screening
upon building entry, exclusion of visitors from the facility, and institution of telework in remote offices or at home, isolation of confirmed COVID-19 patients, conversion of COVID-19 wards to negative pressure environments, use of PAPRs) or N95 respirators along with PPE by staff. |
| Dong 2020 | China | Observational
Homes |
Household | 135 cases; 259 close contacts | Not reported | Not reported | No | Not reported | |
| Doung-ngern 2020 | Thailand | Retrospective case-control
Various March to April 2020 |
Local | 3 large clusters in nightclubs, boxing
stadiums, and a state enterprise office |
RT-PCR | Not reported | No | Not reported | Hygiene measures: Consistent wearing of masks,
handwashing, and social distancing in public. |
| Draper 2020 | Australia | Observational Various
March to April 2020 |
Local
Household Nosocomial |
28 cases; 445 close contacts | RT-PCR | Within 2 weeks of exposure to
infected case |
No | Not reported | Cruise ship, homes, aircraft, hospital |
| Dub 2020 | Finland | Retrospective cohort (2)
School and Household |
Local
Household |
School and household contacts of 2 index
cases who contracted COVID-19 at school |
RT-PCR
Serology |
Serology: >4 weeks post-exposure | No | MNT titre of ≥ 6
considered positive FMIA titre 3·4 U/ml considered positive |
|
| Expert Taskforce 2020 | Japan | Observational prospective
Cruise ship February 2020 |
Local | 3,711 persons in cruise ship | RT-PCR | Not reported | No | Not reported | Passengers were allowed a 60-minute period on an exterior
deck each day, during which they were instructed to wear masks, refrain from touching anything, and maintain a 1-meter distance from others. Monitors observed these periods. After each group came a 30-minute period in which the areas were disinfected. Room cleaning was suspended. Food and clean linens were delivered to cabin doors by crew, and dirty dishes and linens were picked up at cabin doors by crew. Only symptomatic close contacts were tested initially. |
| Fateh-Moghadam 2020 | Italy | Observational Various
March to April 2020 |
Community | 2,812 cases; 6,690 community contacts | Not reported | Not reported | No | Not reported | Institutional settings including nursing homes, hospitals, day
and residential centers for the disabled and similar structures, and convents |
| Firestone 2020 | USA | Observational retrospective
Motorcycle rally August-September 2020 |
Local | 51 primary event-associated cases, and 35
secondary or tertiary cases |
RT-PCR
WGS Phylogenetic analysis |
Unclear | No | Not reported |
Secondary cases: Laboratory-confirmed infections in persons
who did not attend the rally but who received SARS-CoV- 2–positive test results after having contact with a person who had a primary case during their infectious period. Tertiary cases were laboratory-confirmed cases in persons who had contact with a person who had a secondary case during their infectious period. SARS-CoV-2 RNA-positive clinical specimens were obtained from clinical laboratories, and |
| Fontanet 2020 | France | Retrospective cohort study
School March to April 2020 |
Local | 661 participants: pupils, their parents
and siblings, as well as teachers and non- teaching staff of a high-school |
Serology | 10 weeks | No | N/A | |
| Fontanet 2020a | France | Retrospective cohort study
Schools April 2020 |
Local | 510 participants: pupils, their parents
and siblings, as well as teachers and non- teaching staff of a high-school |
Serology | 10 weeks | No | N/A | 6 primary schools |
| Gan 2020 | China | Observational retrospective
survey Various January-February 2020 |
Local
Household Community |
1 052 cases in 366 epidemic clusters | Not reported | Not reported | No | Not reported | Family living together, gathering dinner, collective work, ride-
thy-car, other aggregation exposure, |
| Ghinai 2020 | USA | Observational
2 Social gatherings January-March 2020 |
Community | 16 cases (7 confirmed and 9 probable) (1
index case) |
RT-PCR | Not reported | No | Not reported | A birthday party, funeral, and church attendance. |
| Gong 2020 | China | Observational
Various January-February 2020 |
Household
Community |
3 clusters: 5 index cases; 9 close contacts | RT-PCR | Not reported | No | Not reported | Travelling and dining, or were living together |
| Gong 2020 | China | Observational
Karaoke room January 2020 |
Local | 14 people exposed to 2 index cases in a karaoke room | RT-PCR
Serology |
PCR: Within 72 hrs post-exposure
Serology: 6 weeks post-exposure |
No | Not reported | |
| Hamner 2020 | USA | Observational
Choir practice March 2020 |
Local | 1 index case; 60 close contacts | RT-PCR | Within 2 weeks of index case | No | Not reported | |
| Han 2020 | S. Korea | Observational
Spa facility Mar-April 2020 |
Community | Contacts for 10 index cases from Spa
facility |
RT-PCR | Not reported | No | Not reported | |
| Heavey 2020 | Ireland | Observational
School March 2020 |
Local | 6 index cases; 1155 contacts | Not reported | Not reported | No | No | Three paediatric cases and three adult cases of COVID-19 with
a history of school attendance were identified. Exposed at school in the classroom, during sports lessons, music lessons and during choir practice for a religious ceremony, which involved a number of schools mixing in a church environment. |
| Helsingen 2020 | Norway | RCT
Training facilities May-June 2020 |
Local | Members of the participating training
facilities age 18 years or older who were not at increased risk for severe Covid-19 |
RT-PCR
Serology |
Serology: 4 weeks after start
of study |
No | Not reported | Hygiene measures: Avoidance of body contact; 1 metre
distance between individuals at all times; 2 metre distance for high intensity activities; provision of disinfectants at all work stations; cleaning requirements of all equipment after use by participant; regular cleaning of facilities and access control by facility employees to ensure distance measures and avoid overcrowding. Changing rooms were open, but showers and saunas remained closed. All participants were mailed a home-test kit including two swabs and a tube with virus transport medium for SARS-CoV-2 RNA |
| Hendrix 2020 | USA | Observational
Hair salon May 2020 |
Local | Contacts for 2 stylists who tested positive
for COVID-19 |
PCR | Not reported | No | Not reported | Hygiene measures: During all interactions with clients at
salon A, stylist A wore a double-layered cotton face covering, and stylist B wore a double-layered cotton face covering or a surgical mask. |
| Hirschman 2020 | USA | Observational study
Home and social gatherings June 2020 |
Household
Community |
2 index cases; 58 primary and secondary
contacts |
RT-PCR | Unclear | No | Not reported | |
| Hobbs 2020 | USA | Case-control study
University Medical Centre September-November 2020 |
Local
Household Community |
397 children and adolescents: Cases 154;
controls 243 |
RT-PCR | Not reported | No | Not reported | |
| Hoehl 2020 | Germany | Observational
Daycare Centre 12 weeks (June-Sept 2020) |
Local
Community |
Attendees and staff from 50 daycare
centres |
RT-PCR | Not reported | No | Not reported | Hygiene measures: Barring children and staff with symptoms
of COVID-19, other than runny nose, from entering the facilities, as well as denying access to individuals with known exposure to SARS-CoV-2. Access to the facilities was also denied to children if a household member was symptomatic, or was in quarantine due to contact with SARS-CoV-2. Wearing of masks was not mandatory for children or nor staff. The access of caregivers to the facilities was limited. |
| Hong 2020 | China | Observational prospective
Home January-April 2020 |
Household | 9 patients with recurrent infection; 13
close contacts |
RT-PCR
Serology NGS |
After re-admission of index
patients. |
No | Not reported | |
| Hu 2020 | China | Observational retrospective
Various January to April 2020 |
Household
Community |
1178 cases; 15,648 contacts | Not reported | Not reported | No | Not reported | Homes, social events, travel, other settings |
| Hua 2020 | China | Observational retrospective
Home January to April 2020 |
Household | Children and adult contacts from the 314
families |
RT-PCR | Not reported | No | Not reported | |
| Huang 2020 | China | Prospective contact-tracing study
Restaurant, home January 2020 |
Household
Community |
1 indes case; 22 close contacts | RT-PCR | Within 3 days of index cases | No | Not reported | Close contacts quarantined at home or hospital |
| Huang 2020a | Taiwan | Retrospective case series
Various January-April 2020 |
Local
Household Community Nosocomial |
15 primary cases: 3795 close contacts | RT-PCR | Not reported | No | Not reported | Aircraft, home, classroom, workplace, hospital |
| Islam 2020 | Bangladesh | Observational
Various March to June 2020 |
Local
Household Community Nosocomial |
181 cases; 391 close contacts | Not reported | Not reported | No | Not reported | Household, health care facility, funeral ceremony, public
transportation, family members, and others |
| Jia 2020 | China | Observational
Home January to February 2020 |
Household | 11 clusters (n=583) | RT-PCR | Not reported | No | <37 considered
positive |
A
close contact was defined as a person who did not take
effective protection against a suspected or confirmed case 2 d before the onset of symptoms or an asymptomatic infected person 2 d before sampling. Ct-value of 40 or more was defined as negative. |
| Jiang 2020 | China | Observational
Home January to February 2020 |
Household
Community |
8 index cases, 300 contacts | rRT-PCR
WGS Phylogenetic analysis |
Every 24 hours for 2 weeks | No | <37 considered
positive |
Ct value ≥40 was considered negative. The maximum
likelihood phylogenetic tree of the complete genomes was conducted by using RAxML software with 1000 bootstrap replicates, employing the general time-reversible nucleotide substitution mode |
| Jing 2020 | China | Retrospective cohort study
Homes January-February 2020 |
Household | 195 unrelated close contact groups (215
primary cases, 134 secondary or tertiary cases, and 1964 uninfected close contacts) |
RT-PCR | Days 1 and 14 of quarantine | No | Not reported | |
| Jing 2020a | China | Observational study
Homes, public places February 2020 |
Household
Community |
68 clusters involving 217 cases | RT-PCR | Not reported | No | Not reported | |
| Jones 2020 | UK
France |
Observational
Super League Rugby August to October 2020 |
Local | 136: 8 index cases: 28 identified close
contacts and 100 other players |
RT-PCR | Within 14 days of match day | No | Not specified: Ct for index cases 17.8 to 27 |
Close contacts were defined by analysis of video footage
for player interactions and microtechnology (GPS) data for proximity analysis. All participants were within a ≤7-day RT-PCR screening cycle |
| Kang 2020 | S. Korea | Observational
Night clubs April-May 2020 |
Local | 96 primary cases and 150 secondary cases;
5,517 visitors |
Not reported | Not reported | No | Not reported | |
| Kant 2020 | India | Retrospective (contact tracing)
Regional Medical Research Centre May 2020 |
Local
Community Nosocomial |
1 index case diagnosed post-mortem;
number of exposures unclear |
RT-PCR | Unclear | No | Not reported | Contacts traced: People from the market where the index case
had his shop, his treating physicians, people who attended his funeral, family members and friends |
| Kawasuji 2020 | Japan | Case-control study
University Hospital April-May 2020 |
Nosocomial | 28 index cases: 105 close contacts | RT-PCR | Unclear | No | Not reported | Index patients and those with secondary transmission were
estimated based on serial intervals in the family clusters. |
| Khanh 2020 | Vietnam | Retrospective
Aircraft March 2020 |
Community | 1 index case: 217 close contacts | PCR | 4 days after positive test result of
index case |
No | Not reported | Successfully traced passengers and crew members were
interviewed by use of a standard questionnaire, tested for SARS-CoV-2 |
| Kim 2020 | S. Korea | Retrospective observational
Home setting January-April 2020 |
Household | 107 paediatric index cases: 248 household
members of which 207 were exposed |
RT-PCR | Within 2 days of COVID-19
diagnosis of the index case |
No | Ct value of ≤35 is
positive and >40 is negative |
Guardian wore a KF94 (N95 equivalent) mask, gloves, full body
suit (or waterproof long-sleeve gowns) and goggles. |
| Kim 2020a | S. Korea | Case series
Various January-February 2020 |
Household
Community |
1 index case; 4 close contacts | RT-PCR | 4 days post-exposure | No | N/A | 2 household contacts, 1 church contact, 1 restaurant |
| Kim 2020b | S. Korea | Retrospective observational
University hospital February 2020 |
Nosocomial | 4 confirmed cases: 290 contacts | RT-PCR | Within 8 days of index case
diagnosis |
No | Ct <35 was considered positive | Medical staff in the triage room used level-D PPE and everyone
in the hospital was encouraged to wear masks and follow hand hygiene practices. Contact with confirmed COVID-19 cases was frequent among inpatients and medical support personnel. |
| Kumar 2020 | India | Observational
Community March-May 2020 |
Community | 144 source cases: | RT-PCR | Unclear | No | Not reported | Persons with symptoms of ILI and SARI as well as known high-
risk contacts of a confirmed COVID-19 patient were included. |
| Kuwelker 2020 | Norway | Prospective case-ascertained
study Homes Feb-April 2020 |
Household | 112 index cases; 179 household members | Serology | 6–8 weeks after symptom onset
in the index case. |
No | N/A | Single-person households were excluded from the analysis.
Serum samples from index cases and household members were collected 6–8 weeks after symptom onset in the index case. |
| Kwok 2020 | Hong Kong | Retrospective observational
Quarantine or isolation February 2020 |
Local
Household |
53 cases; 206 close contacts | Not reported | Not reported | No | Not reported | A
secondary case referred to the first generation of infection
induced by an index case following contact with this case |
| Ladhani 2020 | UK | Prospective
Care homes April 2020 |
Nosocomial | 6 London care homes reporting a
suspected outbreak (2 or more cases); 254 staff members |
RT-PCR | Not reported | No | Not reported | 254 of 474 (54%) staff members provided a nasal self-swab; 12
were symptomatic at the time of swabbing |
| Ladhani 2020a | UK | Prospective
Care homes April 2020 |
Nosocomial | 6 London care homes reporting a
suspected outbreak (2 or more cases); 254 staff members; 264 residents |
RT-PCR | Not reported | Yes | Unclear: Ct values <35 were cultured | 254 of 474 (54%) staff members provided a nasal self-swab; 12
were symptomatic at the time of swabbing |
| Laws 2020 | USA | Prospective cohort
Home setting March-May 2020 |
Household | 1 pediatric index case: 188
household contacts |
RT-PCR | Study enrollment (day 0); study
close-out (day 14) |
No | Not reported | Index case: household member with earliest symptom onset
(and positive SARS-CoV-2 RT-PCR test result). Community prevalence in the 2 metropolitan areas was low during this time, and both were under stay-at-home orders. All enrolled index case patients and household contacts were followed prospectively for 14 days. Five households were selected for intensive swabbing requiring collection of respiratory specimens from all household members during four interim visits regardless of symptom presence. |
| Laxminarayan 2020 | India | Observational
Various April to August 2020 |
Local
Household Community |
3,084,885 known exposed contacts | Not reported | Not reported | No | Not reported | Individual-level epidemiological data on cases and contacts,
as well as laboratory test results, were available from 575,071 tested contacts of 84,965 confirmed cases. |
| Lee 2020 | S. Korea | Observational
Hospital February-June 2020 |
Household | 12 paediatric cases; 12 guardians as close
contact. All guardians used PPE |
Not reported | Not reported | No | Not reported | |
| Lee 2020a | S. Korea | Observational
Homes February to March 2020 |
Household | 23 close contacts | PCR | Unclear | No | Not reported | |
| Lewis 2020 | USA | Observational
Homes March to April 2020 |
Household | 58 households (Utah, n = 34; Wisconsin
n = 24), 58 primary patients and 188 household contacts |
RT-PCR
Serology |
Not reported | No | Not reported | |
| Li 2020 | China | Observational
Home setting Feb 2020 |
Household | Family cluster of 1 index case: 5 household
contacts |
RT-PCR | One day after index case tested
positive |
No | Not reported | Unknown when index case started shedding virus |
| Li 2020a | China | Observational case series
Home, hospital January-February 2020 |
Household
Nosocomial |
2-family cluster of 1 index case: 7 close
contacts |
Not reported | Not reported | No | Not reported | |
| Li 2020b | China | Retrospective observational
Home January-February 2020 |
Household | 3-family cluster of 3 index cases: 14 close
contacts |
RT-PCR | Every 2–3 days until hospital
discharge. |
No | <38 considered
positive |
|
| Li 2020c | China | Retrospective observational
Home January-March 2020 |
Household | 30 cases from 35 cluster-onset families
(COFs) and 41 cases from 16 solitary-onset families (SOFs) |
Not reported | Not reported | No | Not reported | |
| Li 2020d | China | Observational
Household February to March 2020 |
Household | 105 index patients; 392 household
contacts |
RT-PCR | Within 2 weeks of exposure to
infected case |
No | Not reported | |
| Liu 2020 | China | Retrospective observational
Home setting Feb 2020 |
Household | Family cluster of 1 index case: 7 household
contacts |
RT-PCR | Immediately after index case
tested positive |
No | If both the
nCovORF1ab and nCoV-NP showed positive results, COVID-19 infection was considered |
Unclear whether the index case was actually first case |
| Liu 2020a | China | Retrospective case series
Hospital January 2020 |
Nosocomial | 30 HCWs with direct contact with patients | RT-PCR | Not reported | No | <40 considered
positive |
30 cases have a history of direct contact with patients with
neo-coronary pneumonia (within 1 m), 1 to 28 contacts, an average of 12 (7,16) contact times, contact time of 0.5 to 3.5 h, the average cumulative contact time of 2 (1.5, 2.7)h. |
| Liu 2020b | China | Retrospective cohort study
Various January-March 2020 |
Household
Community Nosocomial |
1158 index cases: 11,580 contacts | RT-PCR | Every several days | No | Not reported | Homes, social venues, various types of transportations |
| Liu 2020c | China | Prospective observational | Unclear | 147 asymptomatic carriers: 1150 close
contacts |
RT-PCR | Not reported | No | Not reported | RT-PCR for asymptomatic carriers - testing method not
described for close contacts |
| López 2020 | USA | Retrospective contact tracing
School setting April-July 2020 |
Local
Household |
12 index pediatric cases: 101 facility
contacts; 184 overall contacts |
RT-PCR | Not reported | No | Not reported | Index case: first confirmed case identified in a person at the
child care facility Primary case: Earliest confirmed case linked to the outbreak. Overall attack rates include facility-associated cases, nonfacility contact cases iand all facility staff members and attendees and nonfacility contacts |
| Lopez Bernal 2020 | UK | Observational
Homes January to March 2020 |
Household
Community |
233 households with two or more people;
472 contacts. |
PCR | Unclear | No | Not reported | Healthcare workers, returning travellers and airplane
exposures were excluded. |
| Lucey 2020 | Ireland | Observational
Hospital March-May 2020 |
Nosocomial | 5 HCWs in cluster 1; 2 HCWs in cluster 3;
HCW in cluster 2 not specified; 52 patients infected with SARS-CoV-2; |
RT-PCR
WGS Phylogenetic analysis |
Not reported | No | Not reported | SARS-CoV-2 RNA was extracted from nasopharyngeal swabs
obtained from COVID-19 cases and their corresponding HCWs were sequenced to completion. HA COVID-19 was classified into two groups according to the length of admission: >7 days and >14 days. The majority of patients required assistance with mobility (65%) and selfcare (77%) |
| Luo 2020 | China | Observational retrospective
Public transport January 2020 |
Community | 1 index case; 243 close contacts | RT-PCR | Within 2 weeks of exposure to
index case |
No | Not reported | The tour coach was with 49 seats was fully occupied with all
windows closed and the ventilation system on during the 2.5-hour trip. |
| Luo 2020a | China | Prospective cohort study
Various January to March 2020 |
Household
Community Nosocomial |
391 index cases; 3410 close contacts | RT-PCR
Serology |
Every 24 hours. | No | Not reported | Homes, public transport; healthcare settings, entertainment
venues, workplace, multiple settings |
| Lyngse 2020 | Denmark | Retrospective
Homes February to July 2020 |
Household | 990 primary cases; 2226 household
contacts |
Not reported | Within 14 days of exposure to
primary case |
No | Not reported | Secondary cases: those who had a positive test within 14
days of the primary case being tested positive. 3 phases of epidemic examined. Assumed that the secondary household members were infected by the household primary case, although some of these secondary cases could represent co-primary cases. A longer cutoff time period could result in misclassification of cases among household members with somewhere else being the source of secondary infections. |
| Ma 2020 | China | Observational
Medical isolation |
Unclear | 1665 close contacts | RT-PCR | Not reported | No | Not reported | |
| Macartney 2020 | Australia | Prospective cohort study
Educational settings April to May 2020 |
Local | 27 primary cases; 633 contacts | RT-PCR, serology, or both | PCR: 5–10 days after last case
contact if not previously collected Serology: day 21 following last case contact. |
No | Not reported |
Index case: The first identified laboratory-confirmed case
who attended the facility while infectious. A school or ECEC setting primary case was defined as the initial infectious case or cases in that setting, and might or might not have been the index case. Primary case: Initial infectious case or cases in that setting, and might or might not have been the index case Secondary case: Close contact with SARS-CoV-2 infection (detected through nucleic acid testing or serological testing, or both), which was considered likely to have occurred via transmission in that educational setting. |
| Malheiro 2020 | Portugal | Retrospective cohort study
Homes March to April 2020 |
Household | Intervention group (n=98), Control (n=453) | Not reported | Not reported | No | Not reported | The intervention group comprised all COVID-19 confirmed
cases that were either identified as close contacts of an index caseor returned from affected areas and placed under mandatory quarantine, with daily follow-up until laboratory confirmation of SARS-CoV-2 infection. The control group included all COVID-19 confirmed cases that were not subject to contact tracing nor to quarantine measures preceding the diagnosis. |
| Maltezou 2020 | Greece | Retrospective observational
Home setting February to June 2020 |
Household | 203 SARS-CoV-2-infected children; number
of index cases and close contacts unclear |
RT-PCR | Not reported | No | Ct >38 considered
negative |
A
family cluster was defined as the detection of at least 2
cases of SARS-CoV-2 infection within a family. First case was defined as the first COVID-19 case in a family. High, moderate, or low viral load (Ct <25, 25–30 or >30, respectively) |
| Maltezou 2020a | Greece | Retrospective observational
Home setting February to May 2020 |
Household | 23 family clusters of COVID-19; 109
household members |
RT-PCR | Not reported | No | <25, 25–30 or >30 | A
family cluster was defined as the detection of at least 2
cases of SARS-CoV-2 infection within a family. Index case was defined as the first laboratory-diagnosed case in the family. |
| Mao 2020 | China | Cross-sectional study
Home, family gatherings January-March 2020 |
Household
Local |
67 clusters with 226 cases confirmed cases | RT-PCR | Not reported | No | Not reported | |
| Martinez-Fierro 2020 | Mexico | Cross-sectional
June-July 2020 |
Unclear | 19 asymptomatic index cases; 81 contacts | RT-PCR
Serology |
Not reported | No | Not reported | |
| Mponponsuo 2020 | Canada | Observational
Hospital March-April 2020 |
Nosocomial | 5 HCWs were index cases; 39 HCWs (16
underwent testing) and 33 patients were exposed (22 underwent testing) |
RT-PCR | Not reported | No | Not reported | All 5 HCWs had E gene cycle threshold (Ct) values between
10.9 and 30.2. Those exposed to the index HCWs were followed for 30 days |
| Ng 2020 | Singapore | Retrospective cohort study
Various January-April 2020 |
Household
Local Community |
1114 PCR-confirmed COVID-19 index cases
in the community in Singapore. 13 026 close contacts (1863 household, 2319 work, and 3588 social) |
RT-PCR
Serology |
If contacts reported symptoms | No | Not reported |
Lower risk contacts: Other contacts who were with the index
case for 10–30 min within 2 m Contacts who reported symptoms were admitted to the hospital for COVID-19 testing by PCR. |
| Ning 2020 | China | Observational study
Various January-February 2020 |
Household
Local Community |
Local cases: 3,435 close contacts
Imported cases: 3,666 close contacts |
Not reported | Not reported | No | Not reported | Imported cases, farmers' markets, malls and wildlife exposure |
| Njuguna 2020 | USA | Observational
Prison May 2020 |
Local | 98 incarcerated and detained persons | RT-PCR | Not reported | No | Not reported | Unclear how many index or close contacts |
| Ogawa 2020 | Japan | Observational
Hospital |
Nosocomial | 1 index patient; 15 HCWs were contact | RT-PCR
Serology |
RT-PCR: 10th day after exposure
Serology: Before isolation |
No | Not specified | Viral culture performed for only the index patient |
| Paireau 2020 | France | Retrospective observational
Various January to March 2020 |
Household
Local Nosocomial |
735 index cases; 6,082 contacts | RT-PCR | Not reported | No | Not reported | Family, home, work, hospital.
Index case: A case whose detection initiated an investigation of its contacts through contact tracing Only contacts who developed symptoms compatible with COVID-19 were tested for SARS-CoV-2 |
| Park 2020 | S. Korea | Retrospective observational
Various February 2020 |
Local
Household Community |
2 index cases; 328 contacts | RT-PCR | 24 hrs for 37 first contacts;
others within 2 weeks |
No | <40 considered
positive |
Aircraft, home, restaurant, clinic, pharmacy.
Contact tracing of COVID-19 cases was conducted from 1 day before symptom onset or 1 day before the case was sampled. |
| Park 2020a | S. Korea | Observational study
Homes January to March 2020 |
Household
Non-household |
5,706 COVID-19 index patients; 59,073
contacts |
Not reported | Not reported | No | Not reported | |
| Park 2020b | S. Korea | Observational study
Workplace, home March 2020 |
Local
Household |
216 employees, 225 household contacts | RT-PCR | Within 2 weeks of report of
infected case |
No | Not reported | Employees do not generally go between floors, and they do
not have an in-house restaurant for meals. Sent a total of 16,628 text messages to persons who stayed >5 minutes near the building X; we tracked these persons by using cell phone location data. |
| Passarelli 2020 | Brazil | Observational
Hospital August 2020 |
Nosocomial | 6 index cases; 6 close contacts | RT-PCR | Not reported | No | <40 considered
positive |
All index cases were asymptomatic hospital visitors |
| Patel 2020 | UK | Retrospective observational
Hospital, community March to April 2020 |
Household | 107 cases; 195 household contacts | RT-PCR | Not tested | No | Not reported | |
| Pavli 2020 | Greece | Observational contact tracing
Aircraft February to March 2020 |
Aircraft | 6 index cases; 891 contacts | RT-PCR | Not reported | No | Not reported | A COVID-19 case was defined at that time as a case with
signs and symptoms compatible with COVID-19 in a patient with laboratory-confirmed SARS-CoV-2 infection, recent travel history to a country with evidence of local transmission of SARS-CoV-2 or close contact with a laboratory-confirmed case |
| Phiriyasart 2020 | Thailand | Observational
Homes April 2020 |
Household | 471 household contacts | RT-PCR | Within 5 days of exposure | No | Not reported | |
| Poletti 2020 | Italy | Observational
February-April 2020 |
Unclear | 5,484 close contacts from clusters | RT-PCR
Serology |
Not reported | No | Not reported | Only contacts belonging to clusters (i.e. groups of contacts
identified by one positive index case) were included. 1,364 (25%) were tested with only RT-PCR, 3,493 (64%) with only serology at least a month after the reporting date of their index case and 627 (11%) were tested both by RT-PCR and serology. |
| Pung 2020 | Singapore | Observational
Various February 2020 |
Local
Community |
425 close contacts from 3 clusters; index
case unclear |
PCR
WGS Phylogenetic analysis |
Not reported | No | Not reported | Company conference, church, tour group.
Close contacts under quarantine for 14 days from last exposure to the individual with confirmed COVID-19, either at home or at designated government quarantine facilities. |
| Pung 2020a | Singapore | Observational
Homes Up till March 2020 |
Household | 277 were primary or co‐primary cases: 875
household contacts |
Not reported | Not reported | No | Not reported | Household contacts were tested if they showed symptoms of
SARS-CoV-2 infection, or if aged 12 years or below |
| Qian 2020 | Hong Kong | Observational retrospective
Various January to February 2020 |
Local
Household Community |
Unclear | Not reported | Not reported | No | Not reported | Homes, transport, restaurants, shopping and entertainment
venues. Four categories of infected individuals were considered based on their relationship: family members, family relatives, socially connected individuals, and socially non‐connected individuals |
| Ravindran 2020 | Indonesia | Retrospective cohort
Wedding March 2020 |
Local | 41 guests; no. of index cases unclear | RT-PCR | Not reported | No | Not reported |
Primary case: Any person who attended the wedding events
in Bali Indonesia during 15–21 March 2020 and who tested positive. Secondary case: any person who tested positive on SARS- CoV-2 after the 14 day period and who was a close contact of a COVID-19 case from the wedding events. |
| Razvi 2020 | UK | Observational study
Hospital May to June 2020 |
Nosocomial | 2,521 HCWs | Serology | Voluntary first-come, first-served
basis |
No | N/A | |
| Rosenberg 2020 | USA | Observational retrospective
Homes March 2020 |
Household | 229 cases; 498 household contacts | RT-PCR | Not reported | No | Not reported | |
| Roxby 2020 | USA | Observational - cross-sectional
Nursing home March 2020 |
Nosocomial | 80 residents and 62 staff members; no
index case |
RT-PCR | Day 1 and 7 days late | No | No | Residents isolated in their rooms; no communal meals or
activities, no visitors allowed in the facility, staff member screening and exclusion of symptomatic staff members implemented. Enhanced hygiene practices were put into effect, including cleaning and disinfection of frequently touched surfaces and additional hand hygiene stations in hallways for workers to use. All residents were tested again 7 days later. |
| Sang 2020 | China | Case series
Home February 2020 |
Household | 1 index case; 6 family members | Not reported | Within 24 hrs of index case | No | Not reported | Central air conditioner was always running at home |
| Schumacher 2020 | Qatar | Prospective cohort study
Football team June to September 2020 |
Local | 1337; no index cases | RT-PCR
Serology |
RT-PCR: Every 3–5 days
Serology: Every 4 weeks |
No | ≤30 positive | Strict hygiene measures and regular testing.
Two phases, the quarantine phase (entry until exit) and the training and match phase (after quarantine exit until the first test done during the week after the last match. Ct >30 but <40 reactive. 1337 subjects were tested at least once; however, some players and staff joined their team and were gradually included in (or left) the programme during the study period. |
| Schwierzeck 2020 | Germany | Observational
Hospital paediatric dialysis unit |
Nosocomial | 1 index case; 48 contacts | RT-PCR | 24 hrs after index case | No | Not specified |
Outbreak was defined as two or more COVID-19 infections
resulting from a common exposure |
| Shah 2020 | India | Observational
Homes March to July 2020 |
Household | 74 primary cases; 386 household contacts | RT-PCR | Not reported | No | Not reported | |
| Shen 2020 | USA | Observational
Social gathering January to February 2020 |
Household
Community |
1 index case: 539 social and family contacts | RT-PCR | If contact had symptoms | No | Not specified | |
| Sikkema 2020 | Netherlands | Cross-sectional
Hospital March 2020 |
Nosocomial | 1796 HCWs; index case not specified | RT-PCR
WGS Phylogenetic analysis |
N/A | No | <32 considered
positive |
HCWs across 3 hospitals. |
| Son 2020 | S. Korea | Observational study
Homes January to March 2020 |
Household | 108 primary cases; 3223 contacts | RT-PCR | Unclear | No | Not reported | |
| Song 2020 | China | Observational case series
Home January 2020 |
Household | 4 family clusters. 4 index cases: 18 close
contacts |
RT-PCR | 0 to 72 hrs after index case
tested positive |
No | Not reported | |
| Speake 2020 | Australia | Observational retrospective
Aircraft March 2020 |
Aircraft | 241 passengers some of whom had
disembarked from 1 of 3 cruise ships that had recently docked in Sydney Harbour. 6 primary cases initially |
RT-PCR
WGS Phylogenetic analysis |
Within 2 weeks of primary cases | Yes | Not specified |
Primary cases as passengers with SARS-CoV-2 who had been
on a cruise ship with a known outbreak in the 14 days before illness onset and whose specimen yielded a virus genomic sequence closely matching that of the ship’s outbreak strain Secondary cases: Passengers with PCR-confirmed SARS- CoV-2 infection who had not been on a cruise ship with a known SARS-CoV-2 outbreak within 14 days of illness onset and in whom symptoms developed >48 hours after and within 14 days of the flight; or international passengers who had not been on a cruise ship in the 14 days before illness and whose specimens yielded a WGS lineage not known to be in circulation at their place of origin but that closely matched the lineage of a primary case on the flight. |
| Stein-Zamir 2020 | Israel | Observational - cross-sectional
Schools May 2020 |
Local | 1,190 students aged 12–18 years (grades
7–12) and 162 staff members. |
PCR | Unclear | No | Not reported | |
| Sugano 2020 | Japan | Observational retrospective
Music concerts February 2020 |
Local | 1 index case; 72 exposures | RT-PCR | Not reported | No | Not specified | |
| Sun 2020 | China | Observational
Homes |
Household | Family clusters | Not reported | Not reported | No | Not reported | |
| Taylor 2020 | USA | Observational
Skilled nursing facilities April-June 2020 |
Nosocomial | 259 tested residents, and 341 tested HCP | RT-PCR
WGS Phylogenetic analysis |
Weekly serial testing (every
7–10 days) |
No | Not specified | |
| Teherani 2020 | USA | Observational
Homes March to June 2020 |
Household | 32 paediatric cases; 144 household
contacts |
PCR | Within 2 weeks of exposure to
infected case |
No | Not reported | Only children who presented with symptoms concerning for
COVID-19 infection were included. |
| Thangaraj 2020 | India | Observational
Tourist group February 2020 |
Community | 1 index case; 26 close contacts | RT-PCR | Within 24 hrs of index case | No | Not reported | |
| Torres 2020 | Chile | Cross-sectional
Community March-May 2020 |
Community | 1009 students and 235 staff | Serology | 8–10 weeks after school
outbreak |
No | N/A | The school was closed on March 13, and the entire community
was placed in quarantine |
| Tshokey 2020 | Bhutan | Observational
Tourists May 2020 |
Local
Community |
27 index cases; 75 high-risk contacts, 1095
primary contacts; 448 secondary contacts |
RT-PCR | High-risk contacts: minimum of
three times with RT-PCR |
No | ≤ 40 considered
positive |
|
| van der Hoek 2020 | Netherlands | Observational
Household March to April 2020 |
Household | 231 cases; 709 close contacts. 54 families
have 239 participants, 185 of whom are family members. |
RT-PCR
Serology |
Not reported | No | Not reported | |
| Wang 2020 | China | Observational
Home January-February 2020 |
Nosocomial
Household |
25 HCWs, 43 family members | RT-PCR
WGS Phylogenetic analysis |
Not reported | No | Not reported | |
| Wang 2020a | China | Retrospective observational
Home February 2020 |
Household | 85 primary cases: 155 household contacts
in 78 households |
RT-PCR | Not reported | No | <37 considered
positive |
|
| Wang 2020b | China | Retrospective cohort study
Homes February to March 2020 |
Household | 124 primary cases; 335 close
contacts |
RT-PCR | Within 2 weeks of symptom
onset of the primary case |
No | Not reported | |
| Wee 2020 | Singapore | Observational
Tertiary Hospital February to May 2020 |
Nosocomial | 28 index cases; 253 staff close-contacts
and 45 patient close-contacts |
RT-PCR | If patient close-contacts or
staff close-contacts developed symptoms |
No | Not specified | Infection control bundle was implemented comprising
infrastructural enhancements, improved PPE, and social distancing between patients. Patients were advised to wear surgical masks, to remain within their room or cohorted cubicle at all times, and to avoid mingling with each other. |
| Wendt 2020 | Germany | Observational
Hospital March 2020 |
Nosocomial | 1 index case physician; 187 contacts with
HCWs and 67 contacts with patients - 23 high-risk contacts in total |
RT-PCR
Serology |
5-days post exposure (5 & 10 days
post exposre for high-risk contacts |
No | <36 or <39 considered positive | All high-risk contacts and the index physician were examined
serologically on days 15 or 16 and days 22 or 23 after exposure. |
| Wolf 2020 | Germany | Observational case series
Hospital quarantine January-February 2020 |
Household | Family cluster: 1 index case, 4 close
contacts |
RT-PCR | 5-days after index case tested
positive |
No | Not reported | The parents were asked to wear masks; wearing masks was
not practical for the children. |
| Wong 2020 | Hong Kong | Observational
Hospital February 2020 |
Nosocomial | 1 index case in AIIR: 71 staff and 49 patients | RT-PCR | End of 28-day surveillance | No | Not specified | |
| Wood 2020 | UK | Retrospective cohort
HCW homes |
Household | 241,266 adults did not share a household
with young children; 41,198, 23,783 and 3,850 shared a household with 1, 2 and 3 or more young children |
PCR | Not reported | No | Not reported | Primary exposure was the number of children aged 0 to 11
years in each household. |
| Wu 2020 | China | Retrospective cohort study
Various January-February 2020 |
Household
Local Community |
144 cases, 2994 close contacts | Not reported | Not reported | No | Not reported | Shared transport, visit, medical care, household, brief contact. |
| Wu 2020a | China | Prospective observational
Homes February to March 2020 |
Household | 35 index cases; 148 household contacts | Not reported | Not reported | No | Not reported | All consecutive patients with probable or confirmed COVID-
19 admitted to the Fifth Affiliated Hospital of Sun Yat-sen University from 17 January to 29 February 2020 were enrolled. All included patients and their household members were interviewed |
| Xie 2020 | China | Cross-sectional
Home January-February 2020 |
Household | 2 family clusters with 61 residents (5 cases) | RT-PCR | 7 days after primary or index
cases diagnosed |
No | Not reported | |
| Xin 2020 | China | Prospective cohort study
Homes January to March 2020 |
Household | 31 primary cases; 106 household contacts | RT-PCR | Not reported | No | Not reported | |
| Yang 2020 | China | Observational cohort study
Home quarantine February-May 2020 |
Household
Local |
93 recurrent-positive patients; 96 close
contacts and 1,200 candidate contacts |
RT-PCR
Serology |
Within 14 days post-exposure | Yes | ≤ 40 considered
positive |
|
| Yau 2020 | Canada | Retrospective cohort study
Hospital dialysis unit April 2020 |
Nosocomial | 2 index cases; 330 contacts (237 patients
and 93 staff) |
RT-PCR | Not reported | No | Not reported | All symptomatic contacts were referred for testing but
asymptomatic household contacts were not routinely tested as per public health protocols at the time. |
| Ye 2020 | China | Observational
Religious gathering January-February 2020 |
Local
Community |
66 confirmed cases and 15 asymptomatic
infections: 1,293 close contacts |
RT-PCR | Not reported | No | Not reported | All close contacts were quarantined |
| Yoon 2020 | S. Korea | Observational
Childcare Centre February-March 2020 |
Local | 1 index case: 190 persons (154 children
and 36 adults) were identified as contacts; 44 were defined as close contacts (37 children and 7 adults) |
PCR | 8–9 days after the last exposure | No | <37 considered positive | Wearing masks, more frequent hand hygiene, and disinfection
of the environment were required before the child index case tested positive. |
| Yousaf 2020 | USA | Survey: cross-sectional
Tertiary-care referral facility June 8 to July 8, 2020 |
Household | 198 household contacts; index cases not
specified |
RT-PCR | Day 1 of study | No | Not reported | |
| Yu 2020 | China | Observational study
Homes January to February 2020 |
Household | 560 index cases; 1587 close contacts | Not reported | Within 2 weeks of exposure to
primary case |
No | Not reported | Exposure environments included workplace, medical centre,
etc. Contact methods included eating or living together, sleeping together, living in same house, etc |
| Yung 2020 | Singapore | Observational prospective
Homes March to April 2020 |
Household | 137 households, 213 paediatric contacts | Not reported | Unclear | No | Not reported | |
| Zhang 2020 | China | Retrospective Observational
Aircraft March-April 2020 |
Aircraft | 4462 passengers screened for COVID-19
based on close contact |
RT-PCR | Not reported | No | Not reported | All passengers were quarantined after arrival |
| Zhang 2020a | China | Retrospective observational
Various January-March 2020 |
Household
Local Community |
359 cases: 369 close contacts | Not reported | Not reported | No | Not reported | Households, social contact, workplace |
| Zhang 2020b | China | Observational study
Hospital April 2020 |
Household | 3 index cases; 10 close contacts | RT-PCR
Serology |
Not reported | No | <37 considered
positive |
Ct value of 40 or more was defined as a negative test. |
| Zhang 2020c | China | Observational
Quarantine January-February 2020 |
Local
Household |
Multi-family cluster of 22 cases: 93 close
contacts |
RT-PCR | Not specified | No | Not reported | All close contacts were quarantined in centralized facilities. |
| Zhang 2020d | China | Observational
Supermarket January-February 2020 |
Local | 1 index case: 8437 contacts | RT-PCR | Not reported | No | Not reported | |
| Zhuang 2020 | China | Observational study
Various January to February 2020 |
Household
Community |
Cluster outbreaks; 8363 close contacts | Not reported | Not reported | No | Not reported | Family and non-family cases |