With inputs from Dr Monica Vasudev

1042:  Pooled COVID-19 Testing Feasible

Mixing specimens can conserve personal protective equipment (PPE),improve patient care and bring about a significant reduction in staff and patient anxiety. These findings were published on July 20 in the Journal of Hospital Medicine. The study depicted that combining specimens from various low risk inpatients in a single test for SARS-CoV-2 infection will make way for the hospital staff to stretch testing supplies and enable them to provide results at a faster rate for an increased number of patients.

The pooled testing strategy involves combining testing samples taken from multiple people within a single test. If the reports are negative, the pooled testing is beneficial in providing the test results for 3 to 5 people simultaneously, while the testing resources used were that of a single test. In retrospect, the challenge is that if the reports are positive, then every individual whose sample was mixed has to go for a retest as one or more from the group could be infected.

In the present study, all the patients admitted to the hospital including those admitted for observation, underwent testing for SARS CoV-2. Patients who did not have any symptoms or clinical evidence of COVID 19, were considered to be at low risk and underwent pooled testing.  

However, patients with any clinical evidence of COVID 19 (respiratory symptoms or laboratory or radiographic findings)were considered high risk and were excluded from the study.

The study included 530 patients visiting the hospital between April 17 and May 11. 179 cartridges (172 with swabs from three patients and seven with swabs from two patients) were used. The results showed four pooled positive tests, making it necessary for all those study participants to be individually retested leading to an additional use of 11 cartridges. In all, the study made use of 190 cartridges, a number 340 less than if the patients were individually tested.  

The findings from the low-risk patient group was encouraging with the positive rate of 0.8% (4 out of 530); none of the patients from pools tested negative were tested positive later during the course of their hospitalization or developed any evidence of the infection.  

The researchers concluded that pooled testing strategy is most beneficial when 3 to 5 patients are included in a pooled test, however, larger batches increase the risk of having a positive test.  

Pooled testing is primarily based on the COVID 19 positive rate in the population of interest along with the sensitivity of the Reverse Transcriptase-Polymerase Chain Reaction method used for COVID 19 testing. The research findings clearly suggested that the pooled testing could raise the testing capability by 69% or more when the incidence rate of SARS-CoV-2 infection is 10% or lower.   

The authors recommend that asymptomatic population or surveillance groups including students, athletes, and military service members are ideal for pooled testing. Even though the study did not shown any false negative specimen, its limitation is that there is a risk of missing specimens with low concentration of the virus owing to the dilution factor of pooling (false negativespecimens).

Dr KK Aggarwal

President CMAAO