[Paper Review] Purim: a rapid method with reduced cost for massive detection of CoVid-19

Benjamin Isac Fargion, Daniele Fargion+2 more|arXiv (Cornell University)|Mar 26, 2020

COVID-19 diagnosis using AI12 references4 citations

TL;DR

Purim is a novel, low-cost, high-throughput method for mass SARS-CoV-2 screening that pools patient samples into sub-groups, tests them collectively, and uses cross-correlation of results to identify infected individuals with minimal individual testing. It reduces testing costs and time by up to 98% and can screen thousands of people with only 2–3% of the tests required by individual PCR, enabling rapid population-wide testing and early outbreak detection.

ABSTRACT

The CoVid-19 is spreading pandemically all over the world. A rapid defeat of the pandemic requires carrying out on the population a mass screening, able to separate positive from negative cases. Such a cleaning will free a flow of productive population. The current rate and cost of testing, performed with the common PCR (polymerase chain reaction) method and with the available resources, is forcing a selection of the subjects to be tested. Indeed, each one must be examined individually at the cost of precious time. Moreover, the exclusion of potentially positive individuals from screening induces health risks, a broad slowdown in the effort to curb the viral spread, and the consequent mortality rates. We present a new procedure, the Purified by Unified Resampling of Infected Multitudes, in short Purim, able to untangle any massive candidate sample with inexpensive screening, through the cross-correlated analysis of the joint speciments. This procedure can reveal and detect most negative patients and in most cases discover the identity of the few positives already in the first or few secondary tests. We investigate the the two-dimensional correlation case in function of the infection probability. The multi-dimensional topology, the scaled Purim procedure are also considered. Extensive Purim tests may measure and weight the degree of epidemic: their outcome may identify focal regions in the early stages. Assuming hundreds or thousand subjects, the saving both in time and in cost will be remarkable. Purim may be able to filter scheduled flights, scholar acceptance, popular international event participants. The optimal extension of Purim outcome is growing as the inverse of the epidemia expansion. Therefore, the earlier, the better.

Motivation & Objective

• To address the urgent need for rapid, low-cost, large-scale SARS-CoV-2 testing to curb pandemic spread.
• To overcome bottlenecks in current individual PCR testing, which is time-consuming and costly at scale.
• To develop a method that can identify infected individuals efficiently in pooled samples without relying on individual testing for all.
• To enable early detection of outbreaks by measuring and weighting epidemic spread across regions through scalable testing.

Proposed method

• Purim pools N individuals into a single test; if positive, the group is subdivided into sub-groups (e.g., rows and columns) for secondary testing.
• It uses a two-dimensional array of pooled samples—horizontal and vertical sub-groups—enabling cross-correlation to pinpoint infected individuals.
• The method relies on cross-checking results from sub-group tests to identify intersections that indicate positive cases, even in the presence of false positives.
• False positives from 'mirror' or 'shadow' effects are resolved via minimal additional individual testing of suspect candidates.
• The procedure scales to multi-dimensional topologies and can be applied to large populations, such as 10,000 individuals, using 2·N² sub-tests.
• It assumes a low infection probability (<1%) and tolerates sample dilution, remaining effective even with 10–100-fold dilution of viral RNA.

Experimental results

Research questions

• RQ1 Can a pooled testing strategy significantly reduce the number of required PCR tests for large-scale SARS-CoV-2 screening?
• RQ2 How can cross-correlated results from pooled sub-groups be used to identify infected individuals with high accuracy and minimal additional testing?
• RQ3 What is the maximum population size that can be efficiently screened using this method while maintaining cost and time efficiency?
• RQ4 How does the method perform under varying infection prevalence rates, especially in low-prevalence settings?
• RQ5 Can the method be extended to real-world applications such as airport screening, school re-entry, or national testing campaigns?

Key findings

• Purim reduces the number of required tests by 80% to 98% compared to individual testing when screening populations with less than 1% infection prevalence.
• For a population of 10,000 individuals, Purim requires only 2% to 20% of the tests needed for individual PCR, depending on infection rate.
• The method can identify the true positive individuals with high confidence in the first or second round of testing, minimizing the need for follow-up individual tests.
• In a national-scale test of 60 million people, Purim could reduce testing costs to just 2–3% of the cost of individual testing, saving billions in expenses.
• The procedure enables rapid screening of large groups such as flights, schools, or events, allowing safe re-entry of the majority while isolating a few infected individuals.
• The method is most effective when applied early in an epidemic, as its efficiency increases inversely with the rate of disease spread.