Pooled COVID Testing: Questions and Answers
School systems in Maine and many other states will be using “pooled testing” as one strategy for keeping schools safe during COVID. This begs the questions - what is pooled testing — testing done in a pool? This blog is dedicated to elucidating answers to questions around pooled testing, and pooled testings use in schools.
What is pooled testing? Pooled testing is when samples from several individuals are taken at the same time and combined into one sample for PCR testing. If this sample is positive, then everyone in the sample is tested to figure out who is positive. If the sample is negative, everyone tested is presumed to be negative.
Why is pooled testing used? Pooled testing is a strategy used to check groups of people for a disease (COVID) in a more timely, cost-effective manner.
Are schools in Maine using pooled testing? The Maine CDC is offering all schools (public and private) to participate in a pooled testing program for grades K - 6. Schools can opt to participate in the program, but are not required to participate. Approximately 25 states are employing pooled testing this upcoming school year. It is best to check with your school to see if it is included.
Who participates in the pooled testing (and is there a requirement for participation)? Students and all school staff are highly encouraged but not required to participate. Parents will be asked to give consent at the beginning of the school year for their child(ren) to participate. Participants (students and staff) are broken into pooled groups based on their cohorting groups. The number of people in each cohort pool is based upon the prevalence of disease within the community.
How long does it take to get results from the pooled testing? Pooled samples are run by State approved labs. It takes 24-48 hours to get tests back. People remain in school pending results.
What happens if there is a positive pool? If the pool is positive, then everyone within the pool is individually tested with the antigen (previously known as rapid) test. If a positive is found, isolation and quarantining kick in for these people and their contacts. If no one tests positive, everyone is retested the next day with the antigen test. Everyone stays in school until they have been proven positive.
How accurate are the tests? The PCR/NAAT testing is considered to be the gold standard for diagnosing COVID (ie, the best test available) — but that does not mean it is a perfect test. The PCR test gives accurate results (ie, a negative result is truly a negative result) anywhere between 60 - 95% of the time.* The antigen (rapid) test is less accurate — it has a 63 to 79% likelihood of accurately diagnosing COVID.** The antigen test is most accurate (72%) at correctly diagnosing COVID during the first week of illness, when a person is symptomatic.
Should my child(ren) participate in pooled testing? Pooled testing is the best available tool for picking up disease in a large population (ie, schools). No harm is done to children in obtaining the samples (sample collection tickles the nose, but is not painful) and the information yield can be invaluable. While limitations in testing must always be considered, the benefits of this testing definitely outweigh negatives (at least to me).
For more information on pooled testing in Maine schools: https://www.maine.gov/doe/sites/maine.gov.doe/files/2021-05/Pooled%20PCR%20Testing%20FAQ_FINAL_5.7.21%20%28003%29.pdf
*Occurrence and Timing of Subsequent SARS-CoV-2 RT-PCR Positivity Among Initially Negative Patients. Long DR, Gombar S, Hogan CA, Greninger AL, O'Reilly-Shah V, Bryson-Cahn C, Stevens B, Rustagi A, Jerome KR, Kong CS, Zehnder J, Shah NH, Weiss NS, Pinsky BA, Sunshine J. Clin Infect Dis. 2020.
**https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD013705.pub2/full
