176 CMAAO CORONA FACTS and MYTH COVID Pool test
Dr K Aggarwal
With inputs from Dr Monica Vasudev
1042: Pooled COVID-19 Testing Feasible
Combining specimens from several low-risk inpatients in a single test for SARS-CoV-2 infection can allow hospital staff to stretch testing supplies and provide test results quickly for many more patients than they might have otherwise.
This strategy conserves personal protective equipment (PPE)], led to a marked reduction in staff and patient anxiety, and improved patient care.
The researchers published their findings July 20 in Journal of Hospital Medicine.
Pooled testing combines samples from multiple people within a single test. The benefit is if the test is negative, [you know that] everyone whose sample was combined…is negative. So you've effectively tested anywhere from three to five people with the resources required for only one test.
The challenge is that if the test is positive, everyone in that testing group must be retested individually because one or more of them has the infection.
For the current study, all patients admitted to the hospital, including those admitted for observation, underwent testing for SARS CoV-2. Staff in the emergency department designated patients as low risk if they had no symptoms or other clinical evidence of COVID-19; those patients underwent pooled testing.
Patients with clinical evidence of COVID-19, such as respiratory symptoms or laboratory or radiographic findings consistent with infection, were considered high risk and were tested on an individual basis and thus excluded from the current analysis.
Between April 17 and May 11, clinicians tested 530 patients via pooled testing using 179 cartridges (172 with swabs from three patients and seven with swabs from two patients). There were four positive pooled tests, which necessitated the use of an additional 11 cartridges. Overall, the testing used 190 cartridges, which is 340 fewer than would have been used if all patients had been tested individually.
Among the low-risk patients, the positive rate was 0.8% (4/530). No patients from pools that were negative tested positive later during their hospitalization or developed evidence of the infection.
Pooling tests seems to work best for three to five patients at a time.
Larger batches increase the chance of having a positive test.
Pooled testing is mainly dependent on the COVID-19 positive rate in the population of interest in addition to the sensitivity of the [reverse transcriptase-polymerase chain reaction (RT-PCR)] method used for COVID-19 testing.
Pooled testing could increase testing capability by 69% or more when the incidence rate of SARS-CoV-2 infection is 10% or lower.
Asymptomatic population or surveillance groups such as students, athletes, and military service members are [an] interesting population to test using pooling testing because we expect these populations to have low positive rates, which makes pooled testing ideal.
[T]here is risk of missing specimens with low concentration of the virus.
These specimens might be missed due to the dilution factor of pooling (false negative specimens). We did not have a single false-negative specimen in our proof-of-concept study.
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