Study suggests screening every two days, but barriers remain

There may be a safe route to reopening college campuses this fall, researchers found, and it might require a huge uptick in Covid-19 testing — but will this approach work for everyone?

Schools across the U.S. were shuttered in March as the Covid-19 pandemic surged across the nation. And, according to a population-based observational study published in JAMA, this approach may have substantially cut SARS-CoV-2 cases and deaths, as previously reported by BreakingMED. But now, as the fall semester creeps closer and Covid-19 cases continue to rise in the U.S., the question of when and how to reopen schools has been the source of much debate. The National Academies of Sciences, Engineering, and Medicine advocated for prioritizing re-opening, particularly for grades K through 5, and Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, recently suggested that the “default situation” should be that kids return to school, with the caveat that the safety, health, and welfare of children and teachers must be prioritized; meanwhile, teachers across the nation have spoken out regarding a lack of communication on how to reopen safely and the difficulty of being forced to choose between the students in their community and their own personal and familial safety. Teachers unions have been making their demands heard, threatening strikes if schools are reopened without the proper safety precautions in place.

A. David Paltiel, PhD, of the Public Health Modeling Unit at the Yale School of Public Health in New Haven, Connecticut, and colleagues, writing in JAMA Network Open, noted that reopening universities — and particularly residential colleges that have communal housing and shared dining areas — will be particularly challenging. However, their analytic modeling study suggested that it is possible to safely reopen campuses this fall if schools are capable of performing Covid-19 screenings at a frequency beyond what is recommended in CDC guidelines — far, far beyond.

“We believe that there is a safe way for students to return to college in fall 2020,” Paltiel and colleagues wrote. “In this study, screening every 2 days using a rapid, inexpensive, and even poorly sensitive (>70%) test, coupled with strict interventions that keep Rt less than 2.5, was estimated to yield a modest number of containable infections and to be cost-effective.”

However, “This sets a very high bar—logistically, financially, and behaviorally—that may be beyond the reach of many university administrators and the students in their care,” they added.

In an editorial accompanying the study, Elizabeth H. Bradley, PhD, and Ming-Wen An, PhD, of Vassar College in Poughkeepsie, New York, and Ellen Fox, MD, of Fox Ethics Consulting in Upland, California, noted that, while the study by Paltiel et al “is a valuable piece of research that answers an important question regarding the cost-effectiveness of Covid-19 testing under various assumptions,” it also “underestimate[s] the potential success of behavioral interventions coupled with public health efforts to reduce the influx of cases onto campus.” They argued that the study’s findings “should be contextualized and their limitations recognized before they are translated into policy recommendations.”

For their study, Paltiel and colleagues created a hypothetical cohort of 5000 students, of whom 10 were assigned undetected, asymptomatic SARS-CoV-2 infection at the start of the semester.

“The decision and cost-effectiveness analyses were linked to a compartmental epidemic model to evaluate symptom-based screening and tests of varying frequency (i.e., every 1, 2, 3, and 7 days), sensitivity (i.e., 70%-99%), specificity (i.e., 98%-99.7%), and cost (i.e., $10/test-$50/test),” they explained. “Reproductive numbers (Rt) were 1.5, 2.5, and 3.5, defining 3 epidemic scenarios, with additional infections imported via exogenous shocks. The model assumed a symptomatic case fatality risk of 0.05% and a 30% probability that infection would eventually lead to observable Covid-19–defining symptoms in the cohort. Model projections were for an 80-day, abbreviated fall 2020 semester.”

For the purposes of their model, the study authors assumed that, following an 8-hour lag to account for test turnaround and time taken to locate and isolate identified cases, students who received a positive test result and those with Covid-19 symptoms would be moved to an “isolation dormitory,” where their infection would be confirmed and they would receive care, with no further transmissions occurring; students with confirmed results would remain in isolation for 14 days, while students with false positive results would be isolated for 24 hours.

“We assumed a mean time from exposure to both infectiousness and screening detectability of 3 days, a symptomatic case fatality risk of 0.05%, and a 30% probability that infection would eventually lead to observable Covid-19–defining symptoms in this young cohort,” they added.

The study’s primary outcomes were cumulative tests, infections, and costs; daily isolation dormitory census; incremental cost-effectiveness; and budget impact.

“Assuming an Rt of 2.5 and daily screening with 70% sensitivity, a test with 98% specificity yielded 162 cumulative student infections and a mean isolation dormitory daily census of 116, with 21 students (18%) with true-positive results. Screening every 2 days resulted in 243 cumulative infections and a mean daily isolation census of 76, with 28 students (37%) with true-positive results. Screening every 7 days resulted in 1840 cumulative infections and a mean daily isolation census of 121 students, with 108 students (90%) with true-positive results. Across all scenarios, test frequency was more strongly associated with cumulative infection than test sensitivity. This model did not identify symptom-based screening alone as sufficient to contain an outbreak under any of the scenarios we considered. Cost-effectiveness analysis selected screening with a test with 70% sensitivity every 2, 1, or 7 days as the preferred strategy for an Rt of 2.5, 3.5, or 1.5, respectively, implying screening costs of $470, $910, or $120, respectively, per student per semester.”

Paltiel and colleagues pointed out several caveats to their conclusions — for example, they noted that adherence to handwashing, indoor masking, and other safety measures could reduce Rt to best-case levels, making containment possible with weekly testing, whereas relaxing these measures could rapidly increase Rt to worst-case levels and make daily screening a must.

The potential threat of rampant false-positive results “that will inevitably result from repeated screening for low-prevalence conditions,” is another possible factor that could “fuel panic and undermine confidence in the reliability of the monitoring program,” they added. They also pointed out adequate supplies of testing equipment as a barrier to ramped-up screening: “On a college campus with 5000 enrollees, screening students alone every 2 days will require more than 195,000 test kits during the abbreviated semester.”

Bradley, An, and Fox added that the required frequency of testing can vary widely from campus to campus. To demonstrate their point, they applied Paltiel et al’s model using assumptions that were believable for Vassar College:

“2500 students, 5 initially infected (given that we are requiring negative tests before students arrive), an Rt of 1.25 (given that we will have extensive social distancing, masking, and other measures), 1 new infection per week (given that we will limit student movement off campus and significantly reduce student interactions with faculty and employees), and test sensitivity of 80% and specificity of 99% (given that we plan to use a rapid polymerase chain reaction test with high accuracy). The results suggest that even if we only tested every 4 weeks, Vassar College could still maintain a controllable number of infections—a mean isolation census of 5 students (of whom 17% have false-positive test results), with a total of 79 student infections during the semester. Testing every 2 weeks yielded a mean isolation census of 6 students (of whom 31% have false-positive results), with a total of 50 infections during the semester.”

The editorialists concluded that campuses should implement “interlocking strategies” to reduce the influx of Covid-19 from outside the school and limit spread once it hits campus before they commit to throwing resources into testing every two days.

“A balanced approach is needed,” Bradley, An, and Fox wrote. “Testing is important; however, successful colleges will be those that embrace inclusive leadership—collaborating with faculty, students, and employees as well as surrounding communities—to reduce the influx of new infections and to limit spread through the judicious use of social distancing, wearing masks, reducing density, augmenting cleaning and ventilation, and performing robust contact tracing.”

  1. Results from an analytic modeling study suggested that college campuses can safely reopen if they commit to screening students every two days using a rapid Covid-19 test, coupled with behavioral interventions to keep Rt below 2.5.
  2. Both the study authors and editorialists pointed out that this approach faces several logistical, financial, and behavioral barriers that many universities may be unable to overcome.

John McKenna, Associate Editor, BreakingMED™

Paltiel was supported by grant R37 DA015612 from the National Institute on Drug Abuse of the National Institutes of Health. Walensky was supported by the Steve and Deborah Gorlin Research Scholars Award from the Massachusetts General Hospital Executive Committee on Research.

Bradley, An, and Fox reported no disclosures.


Cat ID: 151

Topic ID: 88,151,254,930,190,926,192,927,151,928,925,934