Table 4. Definition of Close Contacts and Other Contacts.
| Study ID | Definitions of close contacts | Definition of other contacts | Contact duration & proximity |
|---|---|---|---|
| Abdulrahman 2020 | Not defined | Not reported | Not reported |
| Adamik 2020 | Not defined | Other cases in each of the infected households were
regarded as secondary cases |
Not reported |
| Afonso 2021 | Not defined | Essential activity workers with COVID‐19, confirmed by the
RT‐PCR, were considered the primary case (index cases) at their households. Their respective infected household contacts were defined as secondary case or secondary transmission cases. |
Not reported |
| Agergaard 2020 | Not defined | Not reported | 2 weeks |
| Akaishi 2021 | 1) Contact with a COVID-19 patient between 2 days
before and 14 days after the onset of symptoms, 2) no usage of masks, 3) distance less than 1 m, and 4) more than 15 min of contact |
Lower-risk contact was defined as being in the same place
as the COVID-19 patients, but without fulfilling the above- described criteria for close contact. |
<1m for >15 min |
| Angulo-Bazán 2021 | Not defined | Not reported | Not reported |
| Armann 2021 | Not defined | Not reported | Not reported |
| Arnedo-Pena 2020 |
Close contacts living in the same household of the
index case and no other sources of transmission apart from the index case could be found. |
Closed contacts from work, social events, relatives live in
other household were excluded and index cases live alone. |
Not reported |
| Atherstone 2021 | CDC definition: <6 feet away from someone with
suspected or confirmed COVID-19 for a cumulative total of 15 minutes or more over a 24-hour period |
Not reported | <1m for >15 min |
| Baettig 2020 |
Close contact: Less than 2 m for more than 15 min in
the last 48 hours before onset symptom of the COVID-19 positive index patient. |
Not reported | <2m for >15 mins 48 hours
before onset symptom of the COVID-19 positive index patient |
| Baker 2020 | Not defined | Not reported | Median cumulative time spent
with the patient 45 mins (10–720 mins) |
| Bao 2020 | Not defined | Not reported | Average stay duration of 2.5
hr daily before the COVID‐19 outbreak. |
| Basso 2020 |
Close contact: ≥15 min at ≤2 m, or during AGPs,
between HCWs and the non-isolated COVID-19 patient |
Not reported | ≤2 m for ≥15 min or during AGP |
| Bays 2020 | Not defined | Not reported | Not specified |
| Bender 2021 | Person with >15 minutes face-to-face contact within a
maximum distance of 2 m to the index case |
Not reported | <2m for >15min |
|
Bernardes-Souza
2021 |
Not defined | Not reported | Not reported |
| Bhatt 2022 | Not defined | Household members: people residing in the same dwelling
as the index participant. |
Not reported |
| Bi 2020 |
Close contacts were identified 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. |
Not specified |
| Bi 2021 | Not defined | Not reported | Not reported |
| Bistaraki 2021 | Not defined | Household contacts were defined as people who lived in
the same house with the confirmed SARS-CoV-2 patient. |
Not reported |
| Bjorkman 2021 | Not defined | Not reported | Not reported |
| Blaisdell 2020 | Not defined | Not reported | 1 week |
| Böhmer 2020 | High risk if they had cumulative face-to-face contact
with a patient with laboratory-confirmed SARS-CoV-2 infection for at least 15 min, had direct contact with secretions or body fluids of a patient with confirmed COVID-19, or, in the case of health-care workers, had worked within 2 m of a patient with confirmed COVID-19 without PPE |
All other contacts were classified as low-risk contacts. | Face-to-face for at least 15
minutes, direct contact without PPE |
| Boscolo-Rizzo 2020 | Not defined | Not reported | Not reported |
| Brown 2020 | Not defined | Not reported | Mean in-class time = 50 minutes |
| Burke 2020 | Either at least 10 minutes spent within 6 feet of the
patient with confirmed COVID-19 (e.g., in a waiting room) or having spent time in the same airspace (e.g., the same examination room) for 0–2 hours after the confirmed COVID-19 patient. |
Not reported | Within 6 feet for at least 10
minutes |
| Calvani 2021 | Not defined | Not reported | Not reported |
| Canova 2020 | Not defined | Not reported | 5 HCWs: >30 minutes
5 HCWs: >15-30 mins 6 HCWs: 5-15 mins 5 HCWs: ≤5 mins |
| Carazo 2021 | Not defined | Not reported | Not reported |
| Cariani 2020 | Not defined | Not reported | Not reported |
| Carvalho 2022 | Not defined | Not reported | Not reported |
| Cerami 2021 | Not defined | Not reported | Not reported |
| Charlotte 2020 | Not defined | Not reported | 2-hours |
| Chaw 2020 |
Close contact: Any person living in the same
household as a confirmed case-patient or someone who had been within 1 m of a confirmed case-patient in an enclosed space for >15 minutes |
Not reported | Within 1m for >15 mins |
| Chen 2020 |
Close contact: All passengers were regarded as close
contacts |
Not reported | Flight duration 5 hours approx |
| Chen 2020a |
Close contacts are persons who have had close
contact with re-positive patients without effective protection with masks, such as living and working together |
Not reported | Not specified |
| Chen 2020b | Not defined | Not reported | Not specified |
| Chen 2020c |
Community contact: Any close contact (being within
6 feet of the case-patient) for a prolonged time (>10 minutes); being an office co-worker of the case- patient with close contact of any duration; contact with infectious secretions from the case-patient; or sharing a healthcare waiting room or area during the same time and up to 2 hours after the case-patient was present. |
Healthcare contact: Face-to-face interaction between
healthcare personnel (HCP) and the case-patient without wearing the full PPE that was recommended at the time of the investigation or potential contact with the case- patient’s secretions by HCP without wearing full PPE. |
>10 mins to 2 hours |
| Cheng 2020 | Not defined | Not reported | Not reported |
| Chu 2020 | Close contact was a person who did not wear
appropriate PPE while having face-to-face contact with a confirmed case for more than 15 minutes during the investigation period. A contact was listed as a household contact if he or she lived in the same household with the index case. Those listed as family contacts were family members not living in the same household. For health care settings, medical staff, hospital workers, and other patients in the same setting were included; close contact was defined by contacting an index case within 2 m without appropriate PPE and without a minimal requirement of exposure time |
Those listed as family contacts were family members not
living in the same household. |
Within 2 m without PPE, face-to-
face contact for >15 minutes |
| Chu 2021 | Not defined | Not reported | Stayed ≥1 night in the household
during case’s infectious period |
| Contejean 2020 |
Close contact: Distance <2 meters for >10 minutes
was defined as close contact |
Not reported | <2 metres for >10 minutes |
| Cordery 2021 | Not defined | Pupil contacts were children who were either in the same
bubble as the Case (Bubble Contact, BC) or in a class within the same school that was adjacent in terms of age-group or proximity (School Contact, SC). Household contacts (HC) were adults and children of any age normally resident with the Case |
Not reported |
|
COVID-19 National
Emergency Response Center 2020 |
Close contact (or high risk exposure)” was being within
2 meters of a COVID-19 case |
Daily contact (or low risk exposure) was defined as having
proximity with a person who was a confirmed COVID-19 case, without having had close contact. |
Not reported |
| Craxford 2021 | Not defined | Not reported | Not reported |
| Danis 2020 | All children and teachers who were in the same class
as the symptomatic pediatric case were considered as high risk contacts and were isolated at home. Moderate/high risk: Person who had prolonged (> 15 min) direct face-to-face contact within 1 m with a confirmed case, shared the same hospital room, lived in the same household or shared any leisure or professional activity in close proximity with a confirmed case, or travelled together with a COVID-19 case in any kind of conveyance, without appropriate individual protection equipment. |
Low risk: Person who had a close (within 1 m) but short
(< 15 min) contact with a confirmed case, or a distant (> 1 m) but prolonged contact in public settings, or any contact in private settings that does not match with the moderate/ high risk of exposure criteria. Negligible risk: Person who had short (< 15 min) contact with a confirmed case in public settings such as in public transportation, restaurants and shops; healthcare personnel who treated a confirmed case while wearing appropriate PPE without any breach identified. |
4 days in chalet |
| Dattner 2020 | Not defined | Not reported | Not reported |
| de Brito 2020 |
Close contact: Close and prolonged contact in the
same room |
Not reported | Not specified |
| Deng 2020 | Not defined | Not reported | Not reported |
| Desmet 2020 | Not defined | Not reported | Not reported |
| Dimcheff 2020 |
Close contact: Within 2 m or 6 feet) with an individual
with confirmed COVID-19 for >15 minutes with the example being exposed to a family member at home who has had a positive COVID-19 nasal swab |
Not reported | Within 2m for >15 mins |
| Dong 2020 | Not defined | Not reported | Not reported |
| Doung-ngern 2020 |
High-risk if they were family members or lived in the
same household as a COVID-19 patient, if they were within a 1-meter distance of a COVID-19 patient longer than 15 minutes; if they were exposed to coughs, sneezes, or secretions of a COVID-19 patient and were not wearing protective gear, such as a mask; or if they were in the same closed environment within a 1-meter distance of a COVID-19 patient longer than 15 minutes and were not wearing protective gear |
Not reported | <15 min vs >15 min, <1m vs >1m |
| Draper 2020 | Close contact was defined as anyone who had face-
to-face contact with a confirmed COVID-19 case for more than 15 minutes cumulatively or continuously (e.g., household setting or healthcare setting without appropriate use of personal protective equipment) or who was in the same room with an infectious case for more than 2 hours (e.g., school room, workplace) while a case was symptomatic or during the 24 hours preceding symptom onset. Aircraft close contacts included passengers seated in the same row as, or in the two rows in front of or behind, an infectious case. If the case was a crew member, the passengers in the area in which the crew member worked were classified as close contacts. Passengers disembarking from cruise ships with high incidence of COVID-19 were also classified as close contacts for surveillance purposes. |
Not reported | Not reported |
| Dub 2020 |
Close household contact, i.e., an individual sharing
the main residence of the secondary case |
A regular household contact, i.e., an individual who would
regularly host or stay in the same residence of a secondary case (stepsibling, divorced parent and new partner). Extended contact, i.e., an individual who would have frequent contact with the secondary case around and after the exposure, for example, grandparents who were involved in caring of the secondary case, according to parents’ reports. |
<2 meters for >10 minutes |
| Expert Taskforce 2020 | Close contact: Cabinmates of confirmed case-patients | Not reported | Not specified |
| Farronato 2021 | Not defined | Not reported | Not reported |
| Fateh-Moghadam 2020 | Contact of a COVID-19 case has been considered any
person who has had contact with a COVID-19 case within a time frame ranging from 48 hours before the onset of symptoms of the case to 14 days after the onset of symptoms |
Not reported | Not reported |
| Firestone 2020 |
Close contact: Being within 6 feet of a patient with
laboratory-confirmed COVID-19 infection for ≥15 minutes |
Not reported | Within 2m for >15 mins |
| Fontanet 2021 | Not defined | Not reported | Not reported |
| Galow 2021 | Not defined | Not reported | Not reported |
| Gamboa Moreno 2021 | Not defined | School contact was a close contact that originated from an
exposure to a case within the school environment. Family or social contact was a contact with a case outside the school environment. |
Not reported |
| Gan 2020 | Not defined | Not reported | Not reported |
| Gaskell 2021 | Not defined | Not reported | Not reported |
| Ge 2021 | A close nonhousehold contact was defined as an
individual exposed (within 1 meter) to an index patient |
A household contact was defined as an individual in the
same household or an individual who dined together with the index patient. |
Within 1m |
| Ghinai 2020 | Not defined | Not reported | Not reported |
| Gold 2021 | Persons exposed to an index patient at school within
6 ft for >15 minutes per day during a 24-hour period while the index patient was infectious (48 hours before to 10 days after symptom onset or, if asymptomatic, 48 hours before to 10 days after specimen collection). |
N/A | <1m for >15 min |
| Gomaa 2021 | Not defined | Not reported | Not reported |
| Gonçalves 2021 | Not defined | Not reported | Not reported |
| Gong 2020 |
Close contact: Anyone who was closely in contact with
a suspected, confirmed and asymptomatic case without effective personal protection (classified protection according to the contact situation, including gloves, medical protective masks, protective face screens, isolation clothing, etc.) since onset of symptoms in the suspected case and confirmed case or the day asymptomatic case’s specimens were collected. The close contact included: (i) living, working, or studying in one house or classroom, (ii) diagnosing, treating, or visiting cases in hospital ward, (iii) being within short distance in the same vehicle, (iv) other situations assessed by the field investigators. |
Not reported | Not reported |
| Gu 2020 | Not defined | Not reported | 5 hrs, no natural ventilation or
face masks; distance between each other <0.5 m |
| Hamner 2020 | Close contact: Within 6 feet of infected case | Not reported | 2.5 hrs within 2 m |
| Han 2020 |
Close contact: Travel was defined as someone who
was in close contact with a confirmed case for over three hours as they travelled to another region aside from Region A. Close contact: meal was defined as someone who was in close contact with a confirmed case for over 30 minutes after having a meal together. |
A casual contact was defined as someone who spent
several minutes with a confirmed case within the same space without any mask on (or a person was established as a contact by an Epidemic intelligence Officer). |
30 mins to 3 hours |
| Hast 2022 | Not defined | Not reported | Not reported |
| Heavey 2020 |
Close contact: Any individual who has had greater
than 15 minutes face-to-face (<2 meters distance*) contact with a case, in any setting. |
Casual contact: Any individual who has shared a closed
space with a case for less than two hours. |
Up to 2 hours in duration |
| Helsingen 2020 | Not defined | Not reported | Not reported |
| Hendrix 2020 | Not defined | Not reported | Not reported |
| Hirschman 2020 |
Close contact: Within 6 feet of an infected person for
at least 15 minutes starting from 2 days before illness onset. |
Not reported | "Hours" |
| Hobbs 2020 |
Close contact: Within 6 feet for ≥15 minutes) with a person with
known COVID-19, school or childcare attendance, and family or community exposures ≤14 days before the SARS-CoV-2 test |
Not reported | Within 2 m for ≥15 minutes |
| Hoehl 2021 | Not defined | Not reported | Not reported |
| Hong 2020 | Anyone who ever came within 2 m of a diagnosed
patient without the use of effective personal protective equipment |
Not reported | 258 person-days |
| Hsu 2021 | Not defined | Not reported | Not reported |
| Hu 2020 | A person who had co-travelled on a train within a three-
row seat distance of a confirmed case (index patient) within 14 days before symptom onset. |
Not reported | Not reported |
| Hu 2021 |
Close contacts were defined as individuals who had
close-proximity interactions (within 1 meter) with clinically suspected and laboratory-confirmed SARS- CoV-2 cases, for the period from 2 days before, to 14 days after, the potential infector’s symptom onset. For those exposed to asymptomatic subjects, the contact period was from 2 days before, to 14 days after, a respiratory sample was taken for real-time RT-PCR testing. Close contacts included, but were not limited to, household contacts (i.e., household members regularly living with the case), relatives (i.e., family members who had close contacts with the case but did not live with the case), social contacts (i.e., a work colleague or classmate), and other close contacts (i.e., caregivers and patients in the same ward, persons sharing a vehicle, and those providing a service in public places, such as restaurants or movie theatres) |
Not reported | Not reported |
| Hu 2021 | Passengers within 3 rows of the index case seat were
considered to be close contacts for estimating the upper bound of risk detailed below |
Lower bound of risk: passengers assumed to be travelling
with their family members or friends if a small group of passengers included one index COVID-19 patient, and passengers seated immediately adjacent to this index patient shared the same departure and destination. |
Within 3 rows of the index case seat |
| Hua 2020 | Not defined | Not reported | |
| Huang 2020 | Close contacts quarantined at home or hospital | Not reported | Not reported |
| Huang 2020a | Not defined | Not reported | Not reported |
| Huang 2021 | Contact with the index case within 2 m without using
appropriate personal protective equipment (PPE) and without a minimum requirement of exposure time in hospital settings. |
Not reported | Not reported |
| Islam 2020 | Close contact was defined as individuals who were
closely linked by contact tracing and were considered a close contact group provided that no PPE was worn having direct face to face contacts. |
Household contacts were defined as individuals who lived
and were sharing the same room and same apartment in the same household. Family contacts were those who are the members of the same family but not living in the same household. |
Face-to-face |
| Jashaninejad 2021 | Person who had exposure or lived with a probable or
confirmed case or had direct and face-to-face contact 2 days before and 14 days after exposure with the index case. |
Not reported | Not reported |
| Jeewandara 2021 | Close contacts were defined as individuals living in
Bandaranayaka watta and who had direct physical contact or associated with cases (distance of 1m) within a period of 2 days from identification of the index case. |
Non-close contacts were defined as those who were living
within the CMC region as the cases, or those who worked with cases in the same causal occupations but were not qualified to be defined as close contacts. |
Within 1m |
| Jia 2020 | 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. |
Not reported | Not reported |
| Jiang 2020 |
Close contacts: Lived with the patients and individuals
who had contact with the patients within 1 meter without wearing proper personal protection. 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 |
Not reported | 1 m |
| Jing 2020 | A
close contact was defined as an individual who
had unprotected close contact (within 1 m) with a confirmed case within 2 days before their symptom onset or sample collection. Individuals who were linked by contact tracing were considered a close contact group |
Not reported | Not reported |
| Jing 2020a | Not defined | Not reported | Not reported |
| Jones 2021 |
Close contacts were defined by analysis of video
footage for player interactions and microtechnology (GPS) data for proximity analysis. |
Not reported | Within 1 m, face-to-face for ≥3
secs |
| Jordan 2022 | Not defined | Not reported | Not reported |
| Kang 2020 | Not defined | Not reported | Not reported |
| Kant 2020 | Not defined | Not reported | Not reported |
| Karumanagoundar 2021 | High-risk contact is defined as any person who was in
proximity with individuals positive for COVID-19 within 2 m of proximity for 15 min. |
Contact: any individual comes in proximity with individuals
positive for COVID-19. Low-risk contact is defined as any person who was in proximity with individuals positive for COVID-19 and sharing same environment but not having high exposure. Household contact: any individual living in the same household and comes in proximity with the individual with COVID-19 confirmed. Community contact: any individual other than living in the same household and comes in proximity with the individual with COVID-19 confirmed. Congregation exposure: individual who have attended the religious congregation event held during February and March 2020 (newspaper reference) |
<2m for >15min |
| Katlama 2022 | Not defined | Not reported | Not reported |
| Kawasuji 2020 | Not defined | Not reported | Not reported |
| Khanh 2020 |
Close contact: <2 m distance for >15 minutes.
Successfully traced passengers and crew members were interviewed by use of a standard questionnaire, tested for SARS-CoV-2 |
Not reported | <2 m distance for >15 minutes. |
| Kim 2020 | Not defined | Household contact: Occurring at least 1 day after but
within 14 days from the last point of exposure. |
2 days during the
presymptomatic period and 1 day during the symptomatic period of the index case. |
| Kim 2020a | Not defined | Not reported | 2 hrs to 4 days |
| Kim 2020b |
Contact was defined as presence in the same room
with COVID-19 confirmed patients, or in the same outpatient clinic or examination room, 30 minutes before and after COVID-19 confirmed patients. Within 2 m of confirmed patients (via CCTV) |
Not reported | Within 2 m of confirmed patients
for 30 mins |
| Kim 2021 | Not defined | Not reported | Face-to-face |
| Kitahara 2022 | Contact with confirmed case for >15 mins without
wearing proper PPE |
Not reported | >15 mins |
| Klompas 2021 | Shared a room with an infected patient, and employees
who had face-to-face contact within 6 feet of an infected employee or patient for at least 15 minutes during which either party was not wearing a mask |
Direct contact: spending ≥15 minutes interacting with staff
or patients on cluster units |
<1m for >15 min |
| Kolodziej 2022 | Not defined | Not reported | Not reported |
| Koureas 2021 | Any person who had unprotected close contact (<2 m,
more than 15 min) with a confirmed case from 2 days before symptom onset (if not available from sample collection) until the patient’s isolation. |
Household Secondary Contact: Any person residing in the
same house/apartment with a Household Index Case. |
<2m for >15min |
| Kumar 2021 | Not defined | Not reported | Not reported |
| Kuwelker 2021 | Not defined | Household members were defined as individuals who resided in the
same household as the index case. |
Not reported |
| Kuwelker 2021 | Not defined | Household members were defined as individuals who
resided in the same household as an index patient. |
Not reported |
| Kwok 2020 |
Close contacts referred to anyone who: (i) provided
care to the case (including a family member or healthcare worker) or had other close physical contact; or (ii) stayed at the same place (including household members or visitors) while the case was ill. |
Not reported | Not reported |
| Ladhani 2020 | Not defined | Not reported | Not reported |
| Ladhani 2020a | Not defined | Not reported | Not reported |
| Laws 2020 | Not defined | Not reported | Unclear |
| Laws 2021 | Not defined | Not reported | Not reported |
| Laxminarayan 2020 | High-risk contacts had close social contact or direct
physical contact with index cases without protective measures High-risk travel exposures—defined as close proximity to an infected individual in a shared conveyance for ≥6 hours |
Low-risk contacts were in the proximity of index cases but
did not meet criteria for high-risk exposure |
Not reported |
| Lee 2020 | Not defined: Frequent close contact | Not reported | >1 m |
| Lee 2020a | Close contact (household contact) | Not reported | Mean contact period was
calculated to be 7.7 days. |
| Lewis 2020 | Not defined | Household contacts were defined as all persons living in
the same household as the primary patient. |
Not reported |
| Li 2020 | Not defined | Not reported | Unclear |
| Li 2020a | Not defined | Not reported | Not reported |
| Li 2020b |
Close contact was defined as an act of sharing a meal,
party, vehicle or living room with a confirmed or latently infected patient within 14 days. |
Not reported | Not reported |
| Li 2020c |
Close contacts were mainly those who have not
taken effective protection from close contact with the suspected and confirmed cases 2 days before symptoms appeared, or the asymptomatic infected persons 2 days before the specimen collection. |
Not reported | Not reported |
| Li 2020d | Not defined | Not reported | Not reported |
| Li 2021a | Not defined | Household contact of an identified case was broadly
defined as a family member or close relative who had unprotected contact with the case within 2 days before the symptom onset or test-positive specimen collection of the case but did not necessarily live at the same address. |
Not reported |
| Li 2021b | Someone who had contact with an index case-patient
without effective protection and within 1 meter, regardless of contact duration. Persons who had close contact with the index case- patient during or 2 days before the index case patient’s illness onset were counted as close contacts |
Not reported | Within 1m regardless of duration |
| Lin 2021 | Those in proximity to cases within 2 days before the
onset of symptoms of suspected and confirmed cases or 2 days before the sampling of asymptomatic infected persons when effective protection or distancing measures were not in effect. Close contacts also included those in proximity to cases in aggregated epidemic settings within 2 weeks before diagnosis such as homes, offices, school classes, and so forth with 2 or more cases of fever and/or respiratory symptoms. |
Not reported | Not reported |
| Liu 2020 | Not defined | Not reported | Unclear |
| Liu 2020a | Direct contact with patients with neo-coronary
pneumonia (within 1 m) |
Not reported | Within 1m for 2.5 hrs |
| Liu 2020b |
Close contacts were defined by the China Prevention
and Control Scheme of COVID-19. |
Not reported | 7.8 (95%CI: 7.0–8.7) close contacts per index case. |
| Liu 2020c | Not defined | Not reported | Not reported |
| Liu 2021 | Not defined | Household contacts were broadly defined as any individual
residing with the index case during the infectious period. |
Not reported |
| López 2020 |
Close contact: Anyone who was within 6 feet of a
person with COVID-19 for at least 15 minutes ≤2 days before the patient’s symptom onset. |
Not reported | ≤1.83m of a person with COVID-
19 for at least 15 minutes ≤2 days before the patient’s symptom onset |
| López 2021 | Not defined | Not reported | Not reported |
| Lopez Bernal 2020 | Household contacts were defined as those living or
spending significant time in the same household. Household contacts, others with direct face to face contact and healthcare workers who had not worn recommended PPE |
Not reported | Not reported |
| Lopez Bernal 2022 | Not defined | Household contacts were defined as those living or
spending substantial time (overnight) in the same household. Other contacts: not classified as close contacts Community contacts: |
Not reported |
| Lucey 2020 |
Close contact: HCW or patient who spent more than
15 minutes face-to-face within 2 metres of a confirmed case or patients who shared a multi-bedded room with a confirmed case for more than 2 hours. |
Not reported | Not reported |
| Luo 2020 | 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. |
Not reported | 1 to 4.5m; up to 2.5 hours on
a bus |
| Luo 2020a |
Close contacts: Anyone who has had contact, without
effective protection regardless of duration of exposure, with 1 or more persons with suspected or confirmed COVID-19 any time starting 2 days before onset of symptoms in persons with a suspected or confirmed case, or 2 days before sampling for laboratory testing of asymptomatic infected persons. |
Not reported | Not reported |
| Lyngse 2020 | Not defined | Not reported | Not reported |
| Ma 2020 | Not defined | Not reported | Longest contact time: 8 days
Shortest contact time: 0 days |
| Macartney 2020 |
Close contacts: Children or staff with face-to-face
contact for at least 15 min, or who shared a closed indoor space for at least 40 min with a case during their infectious period. |
Not reported | Face-to-face contact for at least
15 min, or who shared a closed indoor space for at least 40 min |
| Malheiro 2020 |
Close contacts (high risk)were defined as individuals
who have spent 15 min or more in closeproximity (2 m or less) to, or in a closed space with, a case. |
Not reported | Not reported |
| Maltezou 2020 |
Close contact was defined as a contact of >15 minutes
within a distance of <2 m with a COVID-19 case. |
Household members were defined as persons living in the
same residence. |
>15 minutes within <2 m |
| Maltezou 2020a |
Close contact was defined as a contact of >15 minutes
within a distance of <2 meters with a COVID-19 case |
Household contacts were defined as persons either living
in the same residence or having close contacts with a family member for >4 hours daily in the family residence. |
Household: >4 hours daily
Close contact: >15 minutes within <2 m |
| Mao 2020 | Not defined | Not reported | Not reported |
| Martínez-Baz 2022 | Any person who had face-to-face contact with a
confirmed COVID-19 infected individuals within 2 m for more than a total of 15 minutes without personal protection within a timeframe ranging from two days before to 10 days after the onset of symptoms in the case, or in the two days before 10 days after the sample which led to confirmation was taken from asymptomatic cases |
Not reported | Within 2m for >15 mins |
| Martinez-Fierro 2020 | Individual who has had closer than <6 feet for ≥15 min
with people with a positive diagnosis for COVID-19 , whether they were symptomatic or asymptomatic according to the CDC definition |
Not reported | ≥15 min at a distance of <1.83m |
| McLean 2022 | Not defined | Not reported | Not reported |
| Mercado-Reyes 2022 | Not defined | Not reported | Not reported |
| Metlay 2021 | Not defined | Not reported | Not reported |
| Meylan 2021 | Not defined | Not reported | Not reported |
| Miller 2021 | Not defined | Not reported | Not reported |
| Montecucco 2021 | A person who had exposure or lived with a probable or
confirmed case or had direct and face-to-face contact exposure with the index case in the period between two days before the positive PCR test or two days preceding the onset of COVID-19 symptoms and end of isolation after infection resolution. |
Not reported | Not reported |
| Mponponsuo 2020 | An interaction of >15 minutes at a distance of <1 m | Not reported | >15 minutes at a distance of <1 m |
| Musa 2021 | Not defined | A household contact was defined as any person living
in the same household as the index case at the time of recruitment. |
Not reported |
| Ng 2020 |
Close contacts were individuals who had contact for
at least 30 min within a 2 m distance from the index case. |
Work contacts were defined as individuals who came
into close contact with the index case at work, from 2 days before the onset of symptoms to isolation of the case, to account for pre-symptomatic transmission. Social contacts were defined as individuals who came into close contact with the index case, from 2 days before onset of symptoms to isolation of the case, through social activities. Transport contacts were excluded Lower risk contacts: Other contacts who were with the index case for 10–30 min within 2 m |
At least 30 min within a 2 m |
| Ng 2021 | Not defined | Household contact was defined as all persons living in
the same household of the index patient at diagnosis, regardless of duration or proximity of contact. |
Not reported |
| Ning 2020 | Not defined | Not reported | Unclear |
| Njuguna 2020 | Not defined | Not reported | Unclear |
| Nsekuye 2021 | High risk contacts (red-ring) were those who had come
into unprotected face-to-face contact (within 2 m) or having been in a closed environment (e.g., household members) with a COVID-19 case for >15 min. Unprotected direct contact with infectious secretions of a COVID-19 case was also considered high risk (red-ring: these are immediate family, friends, relatives or co-workers that were more likely to have received exposure to transmission). |
A contact of a COVID-19 case was defined as any person
who had contact with a COVID-19 case within a timeframe ranging from 72 h before the onset of symptoms of the case to 14 days after the onset of symptoms. Low risk contacts were those who had come into contact while masked, within more than 2 m or for less than 15 min. |
<2m for >15min |
| Ogata 2021 | Not defined | Not reported | Not reported |
| Ogawa 2020 | Not defined | Not reported | Not reported |
| Paireau 2022 | Not defined | Not reported | Not reported |
| Pang 2022 | Not defined | Not reported | Not reported |
| Park 2020 | Not defined | Not reported | Not reported |
| Park 2020a | High-risk contact (household contacts of COVID-19
patients, healthcare personnel) |
Household contact was a person who lived in the
household of a COVID-19 patient and a nonhousehold contact was a person who did not reside in the same household as a confirmed COVID-19 patient. |
Not reported |
| Park 2020b | Not defined | Not reported | Not reported |
| Passarelli 2020 | Not defined | Not reported | Not reported |
| Patel 2020 | Not defined | Not reported | Not reported |
| Pavli 2020 |
Close contacts were defined as persons sitting within
a distance of <2 m for >15 min, including passengers seated two seats around the index case and all crew members and persons who had close contact with the index case. |
Not reported | <2 m for >15 min |
| Petersen 2021 | Household members and contacts who were within 2
meters of an infected person for >15 minutes, who had direct physical contact or provided caregiving without using personal protective equipment, or who had similar exposures, were defined as close contacts. |
Not reported | <2m for >15min |
| Pett 2021 | Not defined | Household contact: living or spending significant time in
the same household. High risk: persons in healthcare settings (e.g., healthcare workers, cleaners, visitors) who have not worn recommended PPE OR laboratory workers who have not used appropriate laboratory precautions during the following exposures to the patient. OR Direct contact with the case or their body fluids or their laboratory specimens OR presence in the same room of a healthcare setting when an aerosol generating procedure is undertaken on the case Lower risk: Persons in healthcare settings (e.g., healthcare workers, cleaners) who have worn recommended PPE during exposures to the patient. |
Not reported |
| Phiriyasart 2020 | Close contact was defined as a person who had at
least one of these following criteria : (i) a person who came into close (within 1 meter) contact with, or had a conversation with any patient for >5 minutes, or was coughed or sneezed on by any patient when he/she did not wear appropriate personal protective equipment (PPE), e.g. a face mask, (ii) a person who was in an enclosed space without proper ventilation, e.g. in the same air-conditioned bus/air-conditioned room as any patient , and was within one meter of any patient for >15 minutes without wearing appropriate PPE. High-risk close contact was defined as a close contact who was likely to contract the virus from any patient through exposure to respiratory secretions of any patient while not wearing PPE according to standard precautions. |
A low-risk close contact was defined as a close contact who
was less likely to contract the virus from any patient. This includes close contacts who have not met the definition for high-risk close contacts. |
Not reported |
| Poletti 2020 | Not defined | Not reported | Not reported |
| Powell 2022 | Not defined | Direct contacts are defined as the staff and students who
were asked to self-isolate. Indirect contacts refer to household members of these staff and students. |
Not reported |
| Pung 2020 |
Close contacts: People who spend a prolonged time
within 2 m of a confirmed case |
Other contacts: People who had some interactions with
the case. |
Unclear |
| Pung 2020a | Close household contacts | Not reported | Unclear |
| Qian 2020 | Four categories of infected individuals were considered
based on their relationship: family members, family relatives, socially connected individuals, and socially non-connected individuals |
Not reported | Not reported |
| Ratovoson 2022 | Defined as those who lived in the same house of a
symptomatic index case up to 4 days before symptom onset or of an asymptomatic index case up to 4 days prior to the collection date of the first positive test result. |
Not reported | |
| Ravindran 2020 |
Close contact: Face-to-face contact for greater than
15 minutes cumulative in the period extending from 48 hours before onset of symptoms in a confirmed case; or sharing of closed space with a confirmed case for a prolonged period of time in the period extending from 48 hours before onset of symptoms in a confirmed case. |
Not reported | Face-to-face contact for at least
15 min, or who shared a closed indoor space for prolonged period 48 hrs before onset of symptoms |
| Razvi 2020 | Not defined | Not reported | Not reported |
| Reukers 2021 | Not defined | Not reported | Not reported |
| Robles Pellitero 2021 | Not defined | Not reported | Not reported |
| Rosenberg 2020 | Not defined | Not reported | |
| Roxby 2020 | Not defined | Not reported | Not reported |
| Sakamoto 2022 | Not defined | Not reported | Not reported |
| Sang 2020 | Not defined | Not reported | Not reported |
| Sarti 2021 | Not defined | Not reported | Not reported |
| Satter 2022 | Not defined | A contact was defined as an individual who experienced
any of the following exposures during the 2 days before and the 14 days after the onset of symptoms of a laboratory-confirmed COVID-19 case: (1) face-to-face contact with a confirmed case within 1 m and for more than 15 min (including travel, gossips, tea stall) or (2) direct physical contact with a confirmed COVID-19 case. |
<1m for >15 min |
| Schoeps 2021 | A category-I contact is defined as a person who either
stayed face-to-face (<1·5 meters) with a COVID-19-case for 15 minutes or longer, or in the same room (i.e., irrespective of distance) for 30 minutes or longer |
Not reported | <1.5m for >15 min |
| Schumacher 2021 | Close contact: Approximately 30–90 seconds in close
proximity (<1.5 m) of other players |
Close social contacts (including sharing a car) | 30–90 seconds in close proximity
(<1.5 m) |
| Schwierzeck 2020 | Not defined | Not reported | Not reported |
| Semakula 2021 | Not defined | A contact of a COVID-19 case was defined as any person
who had contact with a COVID-19 case within a timeframe ranging from 72 hours before the onset of symptoms of the case to 14 days after the onset of symptoms |
Not reported |
| Shah 2020 | Household contact was defined as contact sharing
same residential address. |
Not reported | Not reported |
| Shah 2021 | Not defined | Household contact was defined as an individual sharing
shame postal address, and secondary case was defined as individual developing infection within 14 days from last contact with the index case. |
Not reported |
| Shen 2020 |
Close contacts defined as individuals who had close,
prolonged, and repeated interactions with the 2 source cases (Cases 2 and 3). |
All other contacts are defined as casual contacts. | Not reported |
| Sikkema 2020 | Not defined | Not reported | Not reported |
| Son 2020 | Not defined | A contact was defined as anyone who was in contact with a
confirmed case from a day before the symptoms occurred, in a manner that offered the potential for transmission through respiratory droplets |
Not reported |
| Song 2020 | Shared the same bedroom, had dinner together | Not reported | Not reported |
| Sordo 2022 | Not defined | Close contacts were considered to be part of the same
household if they had the same address as the case. |
Not reported |
| Soriano-Arandes 2021 | Not defined | Household contacts were defined as all persons living
in the same household as the first patient diagnosed, regardless of the duration or proximity of the contact |
Not reported |
| Speake 2020 | 2 rows in front and behind infectious passenger on an
airplane |
Not reported | Unclear |
| Stein-Zamir 2020 | Not defined | Not reported | Not reported |
| Stich 2021 | Not defined | Not reported | Not reported |
| Sugano 2020 | Not defined | Not reported | Unclear |
| Sun 2020 | Not defined | Not reported | Not reported |
| Sun 2021 | Not defined | Not reported | Not reported |
| Sundar 2021 | Not defined | Contacts were those who were exposed to the index case
in the pre-symptomatic (2 days prior to symptom onset) or symptomatic period and satisfied at least one of the following: a) persons at residence of index case, b) persons at workplace who were exposed to the index case at close range (less than 6 feet) for ≥15 minutes, and c) persons outside the index case residence or workplace with close range contact ≥15 minutes who are traceable |
<1m for >15 min |
| Tadesse 2021 | Not defined | Not reported | Not reported |
| Tanaka 2021 | Not defined | Not reported | Not reported |
| Tanaka 2022 | Not defined | Not reported | Not reported |
| Taylor 2020 | Not defined | Not reported | Unclear |
| Teherani 2020 | Household contacts (HCs) were defined as an adult
(18 years) or a child (<18 years) who resided in the home with the SIC at the time of diagnosis. |
Not reported | Not reported |
| Thangaraj 2020 | Not defined | Not reported | Unclear |
| Torres 2020 | Not defined | Not reported | Unclear |
| Tsang 2022 | A close contact of a case is defined as any person
who was in close proximity to the case without any personal protection equipment, starting 2 days before the symptom onset of the case or specimen collection if the case was asymptomatic. Close contact settings include but are not limited to (1) living, working, dining or taking classes with the case in the same closed space or in proximity; (2) providing health care to or visiting the case at a hospital; and (3) sharing transportation with and in close proximity to the case (in flights, passengers within 3 rows of seats in the front and back of a case as well as crew members who had been in proximity to a case were considered as close contacts); and (4) other individuals in close proximity to the cases as determined by field investigators. |
Not reported | Not reported |
| Tshokey 2020 | Close friends, roommates, flight seat partner, spouse
or partner, cousin, physician, tour driver |
Primary contacts: Individuals coming in some form of
contact with the confirmed cases such as conveyance in the same cars/flights, encounter in clinics, serving meals, or providing housekeeping services in hotels. Secondary contacts: Individuals coming in contact with the primary contacts |
Unclear |
| Tsushita 2022 | Not defined | Not reported | Not reported |
| van der Hoek 2020 | Not defined | Not reported | |
| Vičar 2021 | Not defined | Not reported | Not reported |
| Wang 2020 | Not defined | Not reported | Unclear |
| Wang 2020a | Not defined | Not reported | Unclear |
| Wang 2020b | Close contact was defined as being within 1 m or 3 feet
of the primary case, such as eating around a table or sitting together watching TV. |
Not reported | Unclear |
| Wee 2020 | Not defined | Not reported | Within 2 m of the index case
for a cumulative time of ≥15 minutes, or who had performed AGPs without appropriate PPE. |
| Wendt 2020 |
High-risk contacts: >15 min face-to-face contact,
sitting in a row behind physician for 45 mins, transfer in an ambulance (45-min drive). |
Not reported | >15 min face-to-face contact |
| White 2022a | A close contact was defined as an individual who was
within 1 m of a case of COVID-19 while wearing a mask, or within 2 m if unmasked, in an indoor or outdoor setting for a cumulative total of 15 min or more over a 24-hour period during the case’s infectious period. |
Not reported | <2m for >15 min |
| White 2022b | A close contact was defined as an individual sitting
within a two-seat radius of an infectious case, where one infectious case was identified on a flight. If any close contact sitting within a two-seat radius of an infectious case tested positive, all passengers on board were then considered close contacts. If there were two or more unrelated infectious cases on board the same flight, all passengers were considered close contacts. |
Not reported | Within a two-seat radius of an
infectious case |
| Wiens 2021 | Not defined | Households were defined as a group of individuals that
sleep under the same roof most nights and share a cooking pot. |
Not reported |
| Wolf 2020 | Not defined | Not reported | Not specified |
| Wong 2020 |
Contact case was defined as a patient or staff who
stayed or worked in the same ward as the index patient. Patients who shared the same cubicle with the index case were considered as ‘patient close contact’. Staff close contact: Staff who had contact within 2 m of the index case for a cumulative time of >15 min, or had performed AGPs, without ‘appropriate’ PPE. |
Casual contacts: All staff and patients who did not fulfil the
pre-defined criteria for close contacts. Casual/low-risk contact: HCW wearing a facemask or respirator only and have prolonged close contact with a patient who was wearing a facemask, or HCW using all recommended PPE or HCW (not using all recommended PPE) who have brief interactions with a patient regardless of whether patient was wearing a facemask. Patient close contacts were quarantined into an AIIR (or quarantine camp if the patient was deemed clinically stable to be discharged from hospital) for 14 days. |
Within 2 m of the index case for
a cumulative time of >15 min |
| Wood 2021 | Not defined | Not reported | Not reported |
| Wu 2020 |
Close contact: Been within 1 metre of a confirmed
case, without effective PPE, within the period for 5 days before the symptom onset in the index case or 5 days before sampling if the index case was asymptomatic. |
Not reported | Within 1 metre of a confirmed case,
without effective PPE |
| Wu 2020a | Household contacts were defined as person who spent
at least 1 night in the house after the symptom onset of the index patient. A household was defined as ≥2 people living together in the same indoor living space. A household index was the first person to introduce SARS-CoV-2 into the household. |
Not reported | At least 1 night |
| Wu 2021 | Close contacts of symptomatic cases were individuals
who had exposed to a confirmed patient of SARSCoV-2 infection without wearing proper PPE (including practising optimal hand hygiene or wearing gloves, and wearing surgical facemasks and gowns) and/or stayed with the case in close proximity (<1m) in a close/ semi-close environment such as household, office, elevator, etc., which should have occurred within two days before the onset of the symptomatic case until when the symptomatic index case was isolated. Close contacts of asymptomatic SARS-CoV-2 infections were people who had a close contact (same definition as above) with the confirmed asymptomatic index case within two days before the asymptomatic case provided specimens to test for SARS-CoV2 to the time when the index case was isolated. |
Not reported | <1m for >15 min |
| Xie 2020 |
Close contact: An individual who has not taken
effective protection when in proximity of suspected or confirmed cases 2 days before the onset of symptoms or 2 days before the collection of asymptomatic specimens. |
Not reported | Unclear |
| Xie 2021 | Not defined | Not reported | Not reported |
| Xin 2020 | Close contacts were defined as persons who had a
short-range contact history for 2 days before the onset of symptoms in COVID-19-suspected and -confirmed cases, or 2 days before the collection of samples from asymptomatic cases without taking effective protective measures, such as family members in the same house, direct caregivers, and medical staff who provided direct medical care, colleagues in the same office or workshop, etc. |
The effective contact duration for the close contacts
was defined as the contact days with index patients with confirmed COVID‐19, which was calculated as the last contact date minus the start contact date, and all dates were corresponding to the definition of close contacts |
The median effective contact
duration with patients with COVID‐19 was 4 (IQR: 1–6) days, with 57 (53.8%) experiencing effective contact between 3 and 11 days, and 9 (8.5%) with effective contact duration > 11 days |
| Yang 2020 | Close contacts: Unprotected exposure. | Candidate contacts: Teachers and classmates | Not reported |
| Yau 2020 | Close unprotected contact with someone who has
tested positive for COVID-19 in the last 14 days |
Not reported | Unclear |
| Ye 2020 | Not defined | Not reported | Not reported |
| Yi 2021 | Not defined | Not reported | Not reported |
| Yoon 2020 |
Close contact was defined as a person who had
face-to-face contact for >15 minutes or who had direct physical contact with the index case-patient. Persons who used the same shuttle bus were also considered to be close contacts. |
Not reported | Face-to-face contact for
>15 minutes or direct physical contact |
| Yousaf 2020 | Not defined | Not reported | Not reported |
| Yu 2020 |
Close contacts were defined as those who lived in the
same household, shared meals, travelled or had social interactions with a confirmed case two days before the onset of COVID-19 symptoms |
Not reported | Not reported |
| Yung 2020 | Not defined | Not reported | Not reported |
| Zhang 2020 | Not defined | Not reported | Not reported |
| Zhang 2020a |
Close contact: Refers to a person who had contact
with index case without using proper protection during 2 days before the index case was tested. |
Not reported | Not reported |
| Zhang 2020b | Not defined | Not reported | Not reported |
| Zhang 2020c |
Close contacts were individuals who lived with a PCR-
confirmed case or interacted with a case within 1 metre from the case without any personal protections. |
Not reported | Within 1m of case |
| Zhang 2020d | Not defined | Not reported | Not reported |
| Zhang 2021 | Not defined | Not reported | Not reported |
| Zhuang 2020 | Not defined | Not reported | Not reported |