Pooling Samples as an Efficient Approach to Regular SARS-CoV-2 Testing in Residential Care Facilities (preprint)

ABSTRACT

Background: Residents of care facilities for the elderly have accounted for a large proportion of all deaths due to COVID-19 globally. In Hong Kong, care home staff are required to undergo testing for SARS-CoV-2 every two weeks, regardless of symptoms. We aimed to optimize testing strategies in order to improve on existing screening programs.Methods: We estimated the reduced sensitivity of pooled PCR testing and used a decision analysis to determine the expected number of tests required. We assumed transmission occurred according to a time-varying Poisson process and that the time from infection to isolation followed a time-varying geometric distribution. We estimated the cumulative number of cases expected under syndromic surveillance, testing without pooling and pooled testing with pool sizes 2, 5 and 10 using an age of infection model.Findings: Assuming a prevalence of 0.02%, pooling 10 samples and conducting testing every two days instead of testing without pooling every 14 days could reduce the average size of an outbreak from between 2 and 14 cases (median 7 cases) to between 1 and 6 cases (median 2 cases). Pooling to allow for daily testing further reduced the average size of an outbreak from 4 cases to 1 case compared to weekly testing.Interpretation: Health authorities can improve on existing screening programs by employing pooled testing procedures and testing individuals more frequently to make the most use of available testing resources.Funding Information This project was supported by a commissioned grant from the Health and Medical Research Fund, Food and Health Bureau, Government of the Hong Kong Special Administrative Region, and the Theme-based Research Scheme (Project No. T11-712/19-N) of the Research Grants Council of the Hong Kong SAR Government.Declaration of Interests BJC consults for Roche, GSK, Moderna, AstraZeneca and Sanofi Pasteur and is supported by the AIR@innoHK program of the Innovation and Technology Commission of the Hong Kong SAR Government. The authors report no other potential conflicts of interest.Ethics Approval Statement The study was approved by the Institutional Review Board of the University of Hong Kong.