Estimation of the serial interval and proportion of pre-symptomatic transmission events of COVID??19 in Ireland using contact tracing data

McAloon, Conor G.; Wall, Patrick; Griffin, John; Casey, Miriam; Barber, Ann; Codd, Mary; Gormley, Eamonn; Butler, Francis; McV Messam, Locksley L.; Walsh, Cathal; Teljeur, Conor; Smyth, Breda; Nolan, Philip; Green, Martin J.; O�Grady, Luke; Culhane, Kieran; Buckley, Claire; Carroll, Ciara; Doyle, Sarah; Martin, Jennifer; More, Simon J.

Abstract

Background

The serial interval is the period of time between the onset of symptoms in an infector and an infectee and is an important parameter which can impact on the estimation of the reproduction number. Whilst several parameters influencing infection transmission are expected to be consistent across populations, the serial interval can vary across and within populations over time. Therefore, local estimates are preferable for use in epidemiological models developed at a regional level. We used data collected as part of the national contact tracing process in Ireland to estimate the serial interval of SARS-CoV-2 infection in the Irish population, and to estimate the proportion of transmission events that occurred prior to the onset of symptoms.

Results

After data cleaning, the final dataset consisted of 471 infected close contacts from 471 primary cases. The median serial interval was 4?days, mean serial interval was 4.0 (95% confidence intervals 3.7, 4.3) days, whilst the 25th and 75th percentiles were 2 and 6?days respectively. We found that intervals were lower when the primary or secondary case were in the older age cohort (greater than 64?years). Simulating from an incubation period distribution from international literature, we estimated that 67% of transmission events had greater than 50% probability of occurring prior to the onset of symptoms in the infector.

Conclusions

Whilst our analysis was based on a large sample size, data were collected for the primary purpose of interrupting transmission chains. Similar to other studies estimating the serial interval, our analysis is restricted to transmission pairs where the infector is known with some degree of certainty. Such pairs may represent more intense contacts with infected individuals than might occur in the overall population. It is therefore possible that our analysis is biased towards shorter serial intervals than the overall population.

Citation

McAloon, C. G., Wall, P., Griffin, J., Casey, M., Barber, A., Codd, M., …More, S. J. (2021). Estimation of the serial interval and proportion of pre-symptomatic transmission events of COVID− 19 in Ireland using contact tracing data. BMC Public Health, 21, Article 805. https://doi.org/10.1186/s12889-021-10868-9

• Journal Article Type: Article
• Acceptance Date: Apr 16, 2021
• Online Publication Date: Apr 27, 2021
• Publication Date: Apr 27, 2021
• Deposit Date: May 17, 2021
• Publicly Available Date: May 18, 2021
• Journal: BMC Public Health
• Print ISSN: 1471-2458
• Electronic ISSN: 1471-2458
• Publisher: Springer Verlag
• Peer Reviewed: Peer Reviewed
• Volume: 21
• Article Number: 805
• DOI: https://doi.org/10.1186/s12889-021-10868-9
• Keywords: Public Health, Environmental and Occupational Health
• Public URL: https://nottingham-repository.worktribe.com/output/5558377
• Publisher URL: https://bmcpublichealth.biomedcentral.com/articles/10.1186/s12889-021-10868-9
• Additional Information: Received: 27 January 2021; Accepted: 16 April 2021; First Online: 27 April 2021; : ; : All methods were carried out in accordance with relevant guidelines and regulations. The study was approved by the National Research Ethics Committee (20-NREC-COV-099). The requirement for informed consent was waived by review board Health Research Declaration Committee (20–025-AF1/COV).; : Not applicable.; : The authors declare that they have no competing interests.