1. first identify which basic units are infected—after all, the entire basic unit needs to be quarantined anyway, and only
2. second to test individuals within the infected basic units to identify individuals who need treatment. In this way, precious testing resources are not wasted on screening individuals from uninfected basic units.
3. The Procedures: To identify the infected basic units, samples (e.g. sputum) from all members of the basic unit are pooled together and—where necessary—concentrated in a microconcentrator and centrifuged to reduce the volume of the sample pool to fit into the sample volume size of commercial virus/pathogen extraction kit and then sent for reaction. Microconcentrators can easily concentrate by a factor of 100X in about 15 minutes.
4. Examples: For example, in a highrise housing complex of 20 storeys of 10 units/storey and average 6 inhabitants/unit, the total number of individuals is 20*10*6 = 1,200 but the number of the basic units is only 200. So, instead of consuming 1,200 test kits and taking proportionately longer time, only 200 test kits and proportionately 1/6 of lab manpower and equipment time are needed to determine which units have infected individuals. Subsequently, only the individual samples from only a handful of those infected units need be separately tested. More importantly, the same test resources can be used to screen 6X as many individuals as before.
5. More examples:
For a cruise ship, several people share a cabin, and the cabin is the basic unit.
For an office tower, the basic unit can be workers sharing a cubicle.
For schools, the basic unit is the pupils sharing the same classroom as well as their teachers, or, even smaller, the section within the classroom according to seating positions.
For a village or town, the inhabitants of each house form the basic unit.
6. Concentrating Pooled Sample Fluids
Exception: In types of the sample in which the pathogen density is very high, such as the sputum of COVID-19 carrier (above 1E3/mL for two weeks after onset of symptom), there is no problem detecting the pathogen from 50 individuals each contributing 20uL(i.e. 1/50 of 1mL) to a pool of 1mL, which is subsequently sent for purification (using magnetic bead technology) to 20uL followed by taking merely 5uL (i.e. 1/4) for a reaction, because each reaction will receive on average 5 copies of the pathogen, which is more than enough for qRT-PCR.
When: Where the pathogen copy number in 1mL is low, like for swabs after the 1st week after symptom onset, the amount taken from the individual sample cannot be substantially below 1mL. In this situtation, in order for the final pooled sample volume to come to 400uL, it is necessary to use microconcentrator and centrifuge to filter out excess water from the pooled sample.
Microconcentrator: The microconcentrator is a one-time use consumable that performs ultrafiltration when centrifuged. Inside the microconcentrator, a filter with pores much smaller than viruses lets solvents flow through but retains virus particles and stops when a given amount of fluid is left in the filter (i.e. it stops itself from drying up). 60 to 100X concentration is possible. Various starting volume (0.5, 2, 4, 15mL; outside diameters 11, 16, 23, and 30mm) are available. Various sizes of the pores (rated by NMWL) too—100kDa is commonly used for coronavirus. Search terms “coronavirus NMWL” turn up numerous research reports that uses microconcentrators to reduce the volume of sample fluid before virus purification and qPCR reaction.