Without an effective treatment or vaccine for COVID-19, we must isolate cases and quarantine people who have been in contact with cases quickly before they interact with other people. When someone is infected with the SARS CoV-2 virus they can spread it to susceptible people as soon as two days later. But how do we identify and isolate infected people before they infect others.
The infectious period often starts about two days before symptoms. People are most infectious on the first day of this period, followed by declining viral levels and eventual clearance (He et al. 2020). There are three ways to identify people who need to be separated from others: symptom monitoring, testing, and contact tracing, all of which involve data essential to collect and employ rapidly.
COVID-19 symptoms data such as fever, cough, and loss of taste or smell are useful to identify cases, thus many institutions are having their students and staff log their symptoms daily. Individuals with symptoms are usually asked to get tested and isolate immediately while waiting for test results to come back.
Robust systems must be in place to ensure that individuals who have symptoms get tested and do not interact with others.
Testing data confirms positive cases for both symptomatic and asymptomatic individuals. Since many people who are infectious do not have symptoms, some institutions are conducting regular surveillance testing for all students and staff multiple times per week so cases can be isolated starting when they are initially infectious. For instance, some are administering non-invasive, saliva-based SARS CoV-2 PCR tests (Ranoa et al. 2020) that have recently been approved through an FDA Emergency Use Authorization (EUA), to everyone in their organization multiple times per week with test results provided within a day. The tests are less expensive than the typical nasopharyngeal swab PCR tests and must be used in conjunction with robust systems that include immediate isolation of cases and contact tracing. Several rapid antigen tests have received EUAs and provide results in 15 minutes, although their sensitivity (i.e., proportion of positives that are correctly identified) is lower than PCR tests (CDC 2020). These tests can be used for screening large numbers of people quickly, but more accurate PCR tests are often used to confirm positive results.
Recent research has shown that high frequency testing with fast reporting ideally 2-3 times per week is more important to stop transmission in a population than test sensitivity (Larremore et al. 2020). Pooled SARS CoV-2 PCR tests reduce costs and antigen tests are now being used by some organizations to quickly screen all of their students or employees. This type of surveillance testing can be effective in conjunction with systems that ensure that cases are put into isolation quickly.
Contact tracing data is used to limit contact between infected people and others and thus reduce transmission. It needs to start immediately when cases are identified, or it is not an effective tool. Since approximately 20-40 percent of people infected with the SARS CoV-2 virus are asymptomatic, it is important to identify contacts of people who test positive (Buitrago-Garcia et al. 2020; Oran et al. 2020).
References
Buitrago-Garcia D, Egli-Gany D, Counotte MJ, Hossmann S, Imeri H, Ipekci AM, Salanti G, Low N. (2020) Occurrence and transmission potential of asymptomatic and presymptomatic SARS-CoV-2 infections: A living systematic review and meta-analysis. PLoS Med. 22;17(9):e1003346.
CDC (2020) www.cdc.gov/coronavirus/2019-ncov/lab/resources/antigen-tests-guidelines.html
He X, Lau EHY, Peng Wu, Xilong Deng, Jian Wang, Xinxin Hao, Yiu Chung Lau,Jessica Y Wong, Yujuan Guan, Xinghua Tan, et al. Temporal dynamics in viral shedding and transmissibility of COVID-19. Nature Medicine, 26(5):672–675, 2020.
Larremore DB, Wilder B, Lester E, Shehata S, Burke JM, Hay JA, Tambe M, Mina MJ, Parker R (2020) Test sensitivity is secondary to frequency and turnaround time for COVID-19 surveillance
medRxiv 2020.06.22.20136309; doi: https://doi.org/10.1101/2020.06.22.20136309
Oran, D. P., & Topol, E. J. (2020). Prevalence of Asymptomatic SARS-CoV-2 Infection: A Narrative Review. Annals of internal medicine, M20-3012. Advance online publication. https://doi.org/10.7326/M20-3012
Ranoa DRE, Holland RL, Alnaji FG, Green KJ, Wang L, Brooke CB, Burke MD, Fan TM, Hergenrother PJ. (2020) Saliva-Based Molecular Testing for SARS-CoV-2 that Bypasses RNA Extraction bioRxiv 2020.06.18.159434; doi: https://doi.org/10.1101/2020.06.18.159434.