Bringing K-12 back to school: Expanded access to testing through
source pooling (Information provided by Ginkgo Bioworks)
What is pooled testing?
Source pooling is a testing method for SARS-CoV-2 that enables widespread testing by multiplying the
number of tests that can be run with the same testing infrastructure thus dramatically reducing cost per
test. With source pooling a large number of samples are combined in the same tube at the source of
collection and sent to the lab together instead of individual samples being sent one at a time. This
collection process reduces bottlenecks at central lab sites and makes it possible to test twenty or more
people using the reagents and cost of processing a single individual sample.
What is classroom pooling?
It’s a method that combines test samples from all individuals in one classroom/group/cohort into one tube that’s then tested.
Source pooling as a surveillance testing method for K-12 reopening
Thus far, few school districts have been able to afford any routine testing; with source pooling, an entire classroom
can be tested together for about $100. Because individual test swabs are combined at the site of collection, an
individual result cannot be given with source pooling, instead providing a population-level result. This information can
be particularly useful to support public health decision making for in-person learning in K-12 schools; using the data
returned in this process, leaders can better make decisions about when to switch to remote learning or when more
individual diagnostic testing is required.
Schools and other congregate settings are a particularly good fit for source pooling because classrooms, activity
groups, and sports teams create natural pods. Especially in lower grades, there is minimal interaction between
classrooms, and in many districts there are protocols already in place for quarantine and contact tracing in classrooms
in the event of a positive case. Students and staff supporting each classroom would provide an anterior nares swab (a
swab of the front of the nostril that can be self-administered by adults and older children, younger kids can be
swabbed by a nurse) and all the swabs from a classroom could be combined together in a large tube and shipped for
processing. In the event of a positive result, a classroom could be quarantined while the students and their families
are retested using a confirmatory diagnostic test. These confirmatory tests could be a combination of traditional
molecular tests and rapid, point-of-care antigen solutions that are now just becoming available.
Scaling across America
There are about 50 million K-12 students in the US. We estimate that costs per person in a pool could be as low as
$5. With pools of 20, it would take about 500,000 pooled tests per day in order to test all those students once per
week at a cost of just $1B per month. Unlike laboratory pooling, where samples are diluted as they are added
together, the number of swabs that can be tested together with source pooling is theoretically limited only by the size
of the tube. As we scale vaccine distribution, it is inevitable that there will continue to be pockets of virus—source
pooling offers an extremely cost effective method to gain the edge in monitoring future outbreaks.
Ginkgo is currently validating this method of testing leveraging our next generation sequencing lab in Boston’s
Seaport, with the target of being able to test hundreds of thousands of individuals per day by early 2021.
However, this method of testing could also be used with any lab that can process SARS-CoV-2 tests, once the lab
has validated the test to detect virus in pooled samples. Such samples can be transferred from the larger tube
containing the swabs into a tube format preferred by any validated lab that has excess capacity, enabling a massive
scaling of the country’s existing testing infrastructure. With logistics support to bring pooled samples to regional labs,
schools across America could use pooled testing as part of their public health response to COVID-19.