scholarly journals Effectiveness of interventions targeting air travellers for delaying local outbreaks of SARS-CoV-2

2020 ◽  
Author(s):  
Samuel Clifford ◽  
Carl A.B. Pearson ◽  
Petra Klepac ◽  
Kevin Van Zandvoort ◽  
Billy J. Quilty ◽  
...  
Keyword(s):  
Symptom Onset ◽  
Additional Benefit ◽  
Stochastic Simulations ◽  
Sensitivity Analyses ◽  
Contact Tracing ◽  
Secondary Infections ◽  
Community Transmission

AbstractBackgroundWe evaluated if interventions aimed at air travellers can delay local SARS-CoV-2 community transmission in a previously unaffected country.MethodsWe simulated infected air travellers arriving into countries with no sustained SARS-CoV-2 transmission or other introduction routes from affected regions. We assessed the effectiveness of syndromic screening at departure and/or arrival & traveller sensitisation to the COVID-2019-like symptoms with the aim to trigger rapid self-isolation and reporting on symptom onset to enable contact tracing. We assumed that syndromic screening would reduce the number of infected arrivals and that traveller sensitisation reduces the average number of secondary cases. We use stochastic simulations to account for uncertainty in both arrival and secondary infections rates, and present sensitivity analyses on arrival rates of infected travellers and the effectiveness of traveller sensitisation. We report the median expected delay achievable in each scenario and an inner 50% interval.ResultsUnder baseline assumptions, introducing exit and entry screening in combination with traveller sensitisation can delay a local SARS-CoV-2 outbreak by 8 days (50% interval: 3-14 days) when the rate of importation is 1 infected traveller per week at time of introduction. The additional benefit of entry screening is small if exit screening is effective: the combination of only exit screening and traveller sensitisation can delay an outbreak by 7 days (50% interval: 2-13 days). In the absence of screening, with less effective sensitisation, or a higher rate of importation, these delays shrink rapidly to less than 4 days.ConclusionSyndromic screening and traveller sensitisation in combination may have marginally delayed SARS-CoV-2 outbreaks in unaffected countries.

scholarly journals Effectiveness of interventions targeting air travellers for delaying local outbreaks of SARS-CoV-2

2020 ◽  
Vol 27 (5) ◽  
Author(s):  
Samuel Clifford ◽  
Carl A B Pearson ◽  
Petra Klepac ◽  
Kevin Van Zandvoort ◽  
Billy J Quilty ◽  
...  
Keyword(s):  
Severe Acute Respiratory Syndrome ◽  
Symptom Onset ◽  
Additional Benefit ◽  
Stochastic Simulations ◽  
Sensitivity Analyses ◽  
Contact Tracing ◽  
Secondary Infections ◽  
Community Transmission

Abstract Background We evaluated if interventions aimed at air travellers can delay local severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) community transmission in a previously unaffected country. Methods We simulated infected air travellers arriving into countries with no sustained SARS-CoV-2 transmission or other introduction routes from affected regions. We assessed the effectiveness of syndromic screening at departure and/or arrival and traveller sensitisation to the COVID-2019-like symptoms with the aim to trigger rapid self-isolation and reporting on symptom onset to enable contact tracing. We assumed that syndromic screening would reduce the number of infected arrivals and that traveller sensitisation reduces the average number of secondary cases. We use stochastic simulations to account for uncertainty in both arrival and secondary infections rates, and present sensitivity analyses on arrival rates of infected travellers and the effectiveness of traveller sensitisation. We report the median expected delay achievable in each scenario and an inner 50% interval. Results Under baseline assumptions, introducing exit and entry screening in combination with traveller sensitisation can delay a local SARS-CoV-2 outbreak by 8 days (50% interval: 3–14 days) when the rate of importation is 1 infected traveller per week at time of introduction. The additional benefit of entry screening is small if exit screening is effective: the combination of only exit screening and traveller sensitisation can delay an outbreak by 7 days (50% interval: 2–13 days). In the absence of screening, with less effective sensitisation, or a higher rate of importation, these delays shrink rapidly to <4 days. Conclusion Syndromic screening and traveller sensitisation in combination may have marginally delayed SARS-CoV-2 outbreaks in unaffected countries.

scholarly journals A mathematically rigorous assessment of the efficiency of quarantining and contact tracing in curbing the COVID-19 epidemic

2020 ◽  
Author(s):  
Amaury Lambert
Keyword(s):  
Mobile Phone ◽  
Symptom Onset ◽  
Matrix Theory ◽  
Infected Individual ◽  
Nonnegative Matrix ◽  
Contact Tracing ◽  
Secondary Infections ◽  
Wide Range ◽  
Stopping Line ◽  
Electronic Interventions

AbstractIn our model of the COVID-19 epidemic, infected individuals can be of four types, according whether they are asymptomatic (A) or symptomatic (I), and use a contact tracing mobile phone app (Y) or not (N). We denote by f the fraction of A’s, by y the fraction of Y’s and by R0 the average number of secondary infections from a random infected individual.We investigate the effect of non-electronic interventions (voluntary isolation upon symptom onset, quarantining private contacts) and of electronic interventions (contact tracing thanks to the app), depending on the willingness to quarantine, parameterized by four cooperating probabilities.For a given ‘effective’ R0 obtained with non-electronic interventions, we use nonnegative matrix theory and stopping line techniques to characterize mathematically the minimal fraction y0 of app users needed to curb the epidemic. We show that under a wide range of scenarios, the threshold y0 as a function of R0 rises steeply from 0 at R0= 1 to prohibitively large values (of the order of 60 – 70% up) whenever R0 is above 1.3. Our results show that moderate rates of adoption of a contact tracing app can reduce R0 but are by no means sufficient to reduce it below 1 unless it is already very close to 1 thanks to non-electronic interventions.

scholarly journals Estimating the generation interval for coronavirus disease (COVID-19) based on symptom onset data, March 2020

2020 ◽  
Vol 25 (17) ◽  
Author(s):  
Tapiwa Ganyani ◽  
Cécile Kremer ◽  
Dongxuan Chen ◽  
Andrea Torneri ◽  
Christel Faes ◽  
...  
Keyword(s):  
Symptom Onset ◽  
Reproduction Number ◽  
Credible Interval ◽  
Sensitivity Analyses ◽  
Contact Tracing ◽  
Generation Interval ◽  
Reproduction Numbers ◽  
Serial Interval ◽  
Distribution Sensitivity ◽  
Interval Distribution

Background Estimating key infectious disease parameters from the coronavirus disease (COVID-19) outbreak is essential for modelling studies and guiding intervention strategies. Aim We estimate the generation interval, serial interval, proportion of pre-symptomatic transmission and effective reproduction number of COVID-19. We illustrate that reproduction numbers calculated based on serial interval estimates can be biased. Methods We used outbreak data from clusters in Singapore and Tianjin, China to estimate the generation interval from symptom onset data while acknowledging uncertainty about the incubation period distribution and the underlying transmission network. From those estimates, we obtained the serial interval, proportions of pre-symptomatic transmission and reproduction numbers. Results The mean generation interval was 5.20 days (95% credible interval (CrI): 3.78–6.78) for Singapore and 3.95 days (95% CrI: 3.01–4.91) for Tianjin. The proportion of pre-symptomatic transmission was 48% (95% CrI: 32–67) for Singapore and 62% (95% CrI: 50–76) for Tianjin. Reproduction number estimates based on the generation interval distribution were slightly higher than those based on the serial interval distribution. Sensitivity analyses showed that estimating these quantities from outbreak data requires detailed contact tracing information. Conclusion High estimates of the proportion of pre-symptomatic transmission imply that case finding and contact tracing need to be supplemented by physical distancing measures in order to control the COVID-19 outbreak. Notably, quarantine and other containment measures were already in place at the time of data collection, which may inflate the proportion of infections from pre-symptomatic individuals.

scholarly journals Empirical evidence on the efficiency of bidirectional contact tracing in COVID-19

2021 ◽  
Author(s):  
Joren Raymenants ◽  
Caspar Geenen ◽  
Nelissen ◽  
Sarah Gorissen ◽  
Emmanuel André
Keyword(s):  
Cohort Study ◽  
Symptom Onset ◽  
Contact Tracing ◽  
Control Group ◽  
Infected Person ◽  
Risk Of Infection ◽  
Modelling Studies ◽  
Large Cohort Study ◽  
Community Transmission ◽  
Standard Contact

Abstract Despite ubiquitous rollout of contact tracing to counteract the spread of COVID-19, few countries have been spared from widespread community transmission, highlighting the need for more effective tracing strategies1,2. Standard contact tracing practice identifies, quarantines and tests persons exposed to an infected person during the contagious period, assumed to start two days before symptom onset or diagnosis3,4. Backward contact tracing intends to identify the source of the infection and persons infected by the same source, either by extending the contact tracing window or investigating suspected source events. These approaches have shown promise in modelling studies, but lack empirical data supporting their efficiency5–7. In the first large cohort study on backward contact tracing for COVID-19, we found that extending the contact tracing window backward by 5 days increased the number of identified contacts by 49.2%. The risk of infection amongst these additional contacts was similar to contacts exposed during the standard tracing window and significantly higher than symptomatic individuals in a control group, leading to an increase of 42.0% in cases identified through contact tracing. The risk was not limited to attendees of suspected source events. Our results imply an urgent need to implement backward contact tracing globally.

scholarly journals A mathematical assessment of the efficiency of quarantining and contact tracing in curbing the COVID-19 epidemic

2021 ◽  
Vol 16 ◽  
pp. 53
Author(s):  
Amaury Lambert
Keyword(s):  
Mobile Phone ◽  
Symptom Onset ◽  
Matrix Theory ◽  
Infected Individual ◽  
Contact Tracing ◽  
Mobile Phone Application ◽  
Digital Interventions ◽  
Secondary Infections ◽  
Wide Range ◽  
Stopping Line

In our model of the COVID-19 epidemic, infected individuals can be of four types, according whether they are asymptomatic (A) or symptomatic (I), and use a contact tracing mobile phone application (Y ) or not (N). We denote by R0 the average number of secondary infections from a random infected individual. We investigate the effect of non-digital interventions (voluntary isolation upon symptom onset, quarantining private contacts) and of digital interventions (contact tracing thanks to the app), depending on the willingness to quarantine, parameterized by four cooperating probabilities. For a given ‘effective’ R0 obtained with non-digital interventions, we use non-negative matrix theory and stopping line techniques to characterize mathematically the minimal fraction y0 of app users needed to curb the epidemic, i.e., for the epidemic to die out with probability 1. We show that under a wide range of scenarios, the threshold y0 as a function of R0 rises steeply from 0 at R0 = 1 to prohibitively large values (of the order of 60−70% up) whenever R0 is above 1.3. Our results show that moderate rates of adoption of a contact tracing app can reduce R0 but are by no means sufficient to reduce it below 1 unless it is already very close to 1 thanks to non-digital interventions.

scholarly journals Investigation of Four Clusters of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Rwanda, 2020

2021 ◽  
Vol 18 (13) ◽  
pp. 7018
Author(s):  
Olivier Nsekuye ◽  
Edson Rwagasore ◽  
Marie Aime Muhimpundu ◽  
Ziad El-Khatib ◽  
Daniel Ntabanganyimana ◽  
...  
Keyword(s):  
High Risk ◽  
Severe Acute Respiratory Syndrome ◽  
Symptom Onset ◽  
Attack Rate ◽  
Positive Sample ◽  
Contact Tracing ◽  
Face To Face ◽  
Laboratory Confirmation ◽  
Closed Environment ◽  
Index Cases

We reported the findings of the first Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) four clusters identified in Rwanda. Case-investigations included contact elicitation, testing, and isolation/quarantine of confirmed cases. Socio-demographic and clinical data on cases and contacts were collected. A confirmed case was a person with laboratory confirmation of SARS-CoV-2 infection (PCR) while a contact was any person who had contact with a SARS-CoV-2 confirmed case within 72 h prior, to 14 days after symptom onset; or 14 days before collection of the laboratory-positive sample for asymptomatic cases. High risk contacts were those who had come into unprotected face-to-face contact or had been in a closed environment with a SARS-CoV-2 case for >15 min. Forty cases were reported from four clusters by 22 April 2020, accounting for 61% of locally transmitted cases within six weeks. Clusters A, B, C and D were associated with two nightclubs, one house party, and different families or households living in the same compound (multi-family dwelling). Thirty-six of the 1035 contacts tested were positive (secondary attack rate: 3.5%). Positivity rates were highest among the high-risk contacts compared to low-risk contacts (10% vs. 2.2%). Index cases in three of the clusters were imported through international travelling. Fifteen of the 40 cases (38%) were asymptomatic while 13/25 (52%) and 8/25 (32%) of symptomatic cases had a cough and fever respectively. Gatherings in closed spaces were the main early drivers of transmission. Systematic case-investigations contact tracing and testing likely contributed to the early containment of SARS-CoV-2 in Rwanda.

scholarly journals Uncovering two phases of early intercontinental COVID-19 transmission dynamics

2020 ◽  
Vol 27 (8) ◽  
Author(s):  
Jing Yang ◽  
Juan Li ◽  
Shengjie Lai ◽  
Corrine W Ruktanonchai ◽  
Weijia Xing ◽  
...  
Keyword(s):  
Phylogenetic Analyses ◽  
International Travel ◽  
Contact Tracing ◽  
Genetic Sequencing ◽  
Response Strategies ◽  
The World ◽  
Containment Measures ◽  
The Usa ◽  
Community Transmission ◽  
Two Phases

Abstract Background The COVID-19 pandemic has posed an ongoing global crisis, but how the virus spread across the world remains poorly understood. This is of vital importance for informing current and future pandemic response strategies. Methods We performed two independent analyses, travel network-based epidemiological modelling and Bayesian phylogeographic inference, to investigate the intercontinental spread of COVID-19. Results Both approaches revealed two distinct phases of COVID-19 spread by the end of March 2020. In the first phase, COVID-19 largely circulated in China during mid-to-late January 2020 and was interrupted by containment measures in China. In the second and predominant phase extending from late February to mid-March, unrestricted movements between countries outside of China facilitated intercontinental spread, with Europe as a major source. Phylogenetic analyses also revealed that the dominant strains circulating in the USA were introduced from Europe. However, stringent restrictions on international travel across the world since late March have substantially reduced intercontinental transmission. Conclusions Our analyses highlight that heterogeneities in international travel have shaped the spatiotemporal characteristics of the pandemic. Unrestricted travel caused a large number of COVID-19 exportations from Europe to other continents between late February and mid-March, which facilitated the COVID-19 pandemic. Targeted restrictions on international travel from countries with widespread community transmission, together with improved capacity in testing, genetic sequencing and contact tracing, can inform timely strategies for mitigating and containing ongoing and future waves of COVID-19 pandemic.

scholarly journals Establishment, contagiousness, and initial spread of SARS-CoV-2 in Canada

FACETS ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 180-194
Author(s):  
Martin Krkošek ◽  
Madeline Jarvis-Cross ◽  
Kiran Wadhawan ◽  
Isha Berry ◽  
Jean-Paul R. Soucy ◽  
...  
Keyword(s):  
Latent Period ◽  
Bayesian Framework ◽  
Contact Tracing ◽  
Transmission Model ◽  
Infectious Period ◽  
Median Reduction ◽  
Community Transmission

This study empirically quantifies dynamics of SARS-CoV-2 establishment and early spread in Canada. We developed a transmission model that was simulation tested and fitted in a Bayesian framework to timeseries of new cases per day prior to physical distancing interventions. A hierarchical version was fitted to all provinces simultaneously to obtain average estimates for Canada. Across scenarios of a latent period of 2–4 d and an infectious period of 5–9 d, the R0 estimate for Canada ranges from a minimum of 3.0 (95% CI: 2.3–3.9) to a maximum of 5.3 (95% CI: 3.9–7.1). Among provinces, the estimated commencement of community transmission ranged from 3 d before to 50 d after the first reported case and from 2 to 25 d before the first reports of community transmission. Among parameter scenarios and provinces, the median reduction in transmission needed to obtain R0 < 1 ranged from 46% (95% CI: 43%–48%) to 89% (95% CI: 88%–90%). Our results indicate that local epidemics of SARS-CoV-2 in Canada entail high levels of stochasticity, contagiousness, and observation delay, which facilitates rapid undetected spread and requires comprehensive testing and contact tracing for its containment.

scholarly journals A renewal equation model to assess roles and limitations of contact tracing for disease outbreak control

2021 ◽  
Vol 8 (4) ◽  
Author(s):  
Francesca Scarabel ◽  
Lorenzo Pellis ◽  
Nicholas H. Ogden ◽  
Jianhong Wu
Keyword(s):  
Deterministic Model ◽  
Infected Individual ◽  
Equation Model ◽  
Renewal Equation ◽  
Contact Tracing ◽  
Calendar Time ◽  
Individual Level ◽  
Total Incidence ◽  
Community Transmission ◽  
The Individual

We propose a deterministic model capturing essential features of contact tracing as part of public health non-pharmaceutical interventions to mitigate an outbreak of an infectious disease. By incorporating a mechanistic formulation of the processes at the individual level, we obtain an integral equation (delayed in calendar time and advanced in time since infection) for the probability that an infected individual is detected and isolated at any point in time. This is then coupled with a renewal equation for the total incidence to form a closed system describing the transmission dynamics involving contact tracing. We define and calculate basic and effective reproduction numbers in terms of pathogen characteristics and contact tracing implementation constraints. When applied to the case of SARS-CoV-2, our results show that only combinations of diagnosis of symptomatic infections and contact tracing that are almost perfect in terms of speed and coverage can attain control, unless additional measures to reduce overall community transmission are in place. Under constraints on the testing or tracing capacity, a temporary interruption of contact tracing may, depending on the overall growth rate and prevalence of the infection, lead to an irreversible loss of control even when the epidemic was previously contained.

scholarly journals Transmission dynamics of the delta variant of SARS-CoV-2 infections in Daejeon, South Korea

2021 ◽  
Author(s):  
Hari Hwang ◽  
Jun-Sik Lim ◽  
Sun-Ah Song ◽  
Chiara Achangwa ◽  
Woobeom Sim ◽  
...  
Keyword(s):  
South Korea ◽  
Symptom Onset ◽  
Credible Interval ◽  
Transmission Dynamics ◽  
Contact Tracing ◽  
Nasopharyngeal Swab ◽  
Strict Adherence ◽  
Virus Shedding ◽  
Viral Shedding ◽  
Asymptomatic Patients

Abstract Background The delta variant of SARS-CoV-2 is now the predominant variant worldwide. However, its transmission dynamics remain unclear. Methods We analyzed all case patients in local clusters and temporal patterns of viral shedding using contact tracing data from 405 cases associated with the delta variant of SARS-CoV-2 between 22 June and 31 July 2021 in Daejeon, South Korea. Results Overall, half of the cases were aged under 19 years, and 20% were asymptomatic at the time of epidemiological investigation. We estimated the mean serial interval as 3.26 days (95% credible interval 2.92, 3.60), and 12% of the transmission occurred before symptom onset of the infector. We identified six clustered outbreaks, and all were associated with indoor facilities. In 23 household contacts, the secondary attack rate was 63% (52/82). We estimated that 15% (95% confidence interval, 13–18%) of cases seeded 80% of all local transmission. Analysis of the nasopharyngeal swab samples identified virus shedding from asymptomatic patients, and the highest viral load was observed two days after symptom onset. The temporal pattern of viral shedding did not differ between children and adults (P = 0.48). Conclusions Our findings suggest that the delta variant is highly transmissible in indoor settings and households. Rapid contact tracing, isolation of the asymptomatic contacts, and strict adherence to public health measures are needed to mitigate the community transmission of the delta variant.

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