Surveillance-based informative testing for detection and containment of SARS-CoV-2 outbreaks on a public university campus: an observational and modelling study

Abstract

Background: Despite severe outbreaks of COVID-19 among colleges and universities across the USA during the Fall 2020 semester, the majority of institutions did not routinely test students. While high-frequency repeated testing is considered the most effective strategy for disease mitigation, most institutions do not have the necessary infrastructure or funding for implementation. Therefore, alternative strategies for testing the student population are needed. Our study detailed the implementation and results of testing strategies to mitigate SARS-CoV-2 spread on a university campus, and we aimed to assess the relative effectiveness of the different testing strategies.

Methods: For this retrospective cohort study, we included 6273 on-campus students arriving to a large public university in the rural USA (Clemson, SC, USA) for in-person instruction in the Fall 2020 semester (Sept 21 to Nov 25). Individuals arriving after Sept 23, those who tested positive for SARS-CoV-2 before Aug 19, and student athletes and band members were not included in this study. We implemented two testing strategies to mitigate SARS-CoV-2 spread during this period: a novel surveillance-based informative testing (SBIT) strategy, consisting of random surveillance testing to identify outbreaks in residence hall buildings or floors and target them for follow-up testing (Sept 23 to Oct 5); followed by a repeated weekly surveillance testing (Oct 6 to Nov 22). Relative changes in estimated weekly prevalence were examined. We developed SARS-CoV-2 transmission models to compare the relative effectiveness of weekly testing (900 daily surveillance tests), SBIT (450 daily surveillance tests), random surveillance testing (450 daily surveillance tests), and voluntary testing (0 daily surveillance tests) on disease mitigation. Model parameters were based on our empirical surveillance data in conjunction with published sources.

Findings: SBIT was implemented from Sept 23 to Oct 5, and identified outbreaks in eight residence hall buildings and 45 residence hall floors. Targeted testing of residence halls was 2·03 times more likely to detect a positive case than random testing (95% CI 1·67-2·46). Weekly prevalence was reduced from a peak of 8·7% to 5·6% during this 2-week period, a relative reduction of 36% (95% CI 27-44). Prevalence continued to decrease after implementation of weekly testing, reaching 0·8% at the end of in-person instruction (week 9). SARS-CoV-2 transmission models concluded that, in the absence of SBIT (ie, voluntary testing only), the total number of COVID-19 cases would have increased by 154% throughout the semester. Compared with SBIT, random surveillance testing alone would have resulted in a 24% increase in COVID-19 cases. Implementation of weekly testing at the start of the semester would have resulted in 36% fewer COVID-19 cases throughout the semester compared with SBIT, but it would require twice the number of daily tests.

Interpretation: It is imperative that institutions rigorously test students during the 2021 academic year. When high-frequency testing (eg, weekly) is not possible, SBIT is an effective strategy to mitigate disease spread among the student population that can be feasibly implemented across colleges and universities.

Funding: Clemson University, USA.

Figure 1

Illustration of the SBIT strategy Sample of six residence halls during the first 10 days of SBIT implementation, three of which were targeted for testing. Points indicate date at test collection. Residence halls with at least two students testing positive for SARS-COV-2 (outbreak threshold) were selected for targeted testing the following available day. Date targeted is the scheduled date of mandatory targeted testing for all students in the residence hall. Because of a lag between the date of test collection and results received, and limits on testing capacity and reduced weekend testing, there was a delay of at least 48 h between when the threshold was exceeded and the targeted testing. SBIT=surveillance-based informative testing.

Figure 2

Weekly SARS-CoV-2 positive cases and prevalence estimates among on-campus students during in-person instruction (A) Observed SARS-CoV-2 positive cases and prevalence estimates for entire population (solid line) and from surveillance tests done during implementation of SBIT (targeted: dotted line; random: dashed line); surveillance testing began on Sept 23, 2020; targeted testing was done by residence hall building (Sept 26–28) or floor (Sept 29 to Oct 5), and repeated weekly surveillance testing was done between Oct 6 and Nov 22. (B) Estimated weekly SARS-COV-2 cases (percentages represent estimated overall prevalence); week 1 (beginning Sept 23) and week 3 (beginning Oct 6) consist of 6 days to account for timing of surveillance testing implementation (Sept 23), transition to targeted testing of residence hall floors (Sept 29), and implementation of weekly testing (Oct 6).

Figure 3

Expected number and prevalence of weekly on-campus SARS-COV-2 positive cases based on SARS-CoV-2 transmission models Three testing strategies are compared here: voluntary testing for symptomatic individuals, random surveillance testing, and SBIT. Both surveillance testing strategies include 450 daily surveillance tests and voluntary testing for symptomatic individuals. The proportion of individuals infected at the semester start was 6·7%. Percentages represent the prevalence of new weekly SARS-COV-2 positive cases relative to the susceptible population at the beginning of each week. Total infections represent the number of infections over the course of 9 weeks. SBIT=surveillance-based informative testing.