'Pooling' coronavirus tests may speed up results, reduce workload for labs

1 year 4 months 2 weeks ago Tuesday, July 21 2020 Jul 21, 2020 July 21, 2020 6:16 AM July 21, 2020 in News - Local

Long wait times and dwindling supplies motivated the U.S. Food and Drug Administration to authorize a testing technique on Saturday. It can potentially provide relief to those two kinks in the COVID-testing assembly line.

The technique may not reach the Valley, but a Brownsville epidemiologist says that might be best right now.

It's called sample pooling. The FDA authorized Quest Diagnostics — a private, for-profit lab present across the U.S. and in the Rio Grande Valley — to begin using this method that works like batch testing.

"UT Health RGV used pool testing early on when we had few positive tests and low capacity," Dr. Michael Dobbs, the chief medical officer at the UT Health Rio Grande Valley School of Medicine, said in a statement. "But I think we are no longer using this technique since our capacity and positive rates are higher."

This method isn't new. Dr. Joseph McCormick, an epidemiologist at UTHealth School of Public Health in Brownsville, explained that in Cameron County they use sample pooling for research to test batches of ten mosquitoes for Dengue and Zika. If one mosquito in the batch is positive for a virus, they'll know the virus is present. It stops there. In humans, the process would continue. 

"If they're all negative, then you would say that everyone who contributed a swab is negative for COVID; but, if you find a positive, you will have to go back and re-test each of them," McCormick said.

Quest Diagnostics will be testing batches of four at a time, according to a news release it shared on Saturday. 

Sample pooling is an appealing method as the turnaround time for test results keeps increasing and supplies keep dwindling across the country. The American Clinical Laboratory Association warned about this in late June. 

"Every country across the globe is in need of essential testing supplies, like pipettes and reagents, and that demand is likely to increase in the coming months," according to the ACLA news release dated June 27.

In the case of Quest Diagnostics, it reports the turnaround time is as long as a week. Quest said it can't change that.

"We want patients and healthcare providers to know that we will not be in a position to reduce our turnaround times as long as cases of COVID-19 continue to increase dramatically across much of the United States," according to a news release dated July 13.

The cost for improving the speed of test results and conservation of supplies can be in accuracy.  

"Specimens with low viral loads may not be detected in sample pools due to the decreased sensitivity of pooled testing," according to the lab's news release on Saturday. 

McCormick said the problem can lead to false negatives. 

"These tests are dependent on how much virus is in a particular swab," McCormick said. "There is some level of dilution and that would mean that your test would have to be pretty sensitive in order to be sure it picks up low levels of virus."

For now, Quest Diagnostics announced it will only start using this method in Chantilly, Virginia, and Marlborough, Mass.

A response from local leaders in public health is still pending. Starr County's health authority, Dr. Jose Vazquez, said the technique may not be useful to them right due to a high incidence rate.  

"With the very high rates of positivity we have, many times 15, 20, 25, 30%, it really is not a very viable approach," McCormick said.

The retesting would have to happen to often to prove effecting in trimming turnaround times and conserving supplies. 

There's still a chance it can work. If the percentage of people testing positive goes down to March or April levels, then sample pooling could be useful.

"Hopefully, we'll get there, but we're not there right now," McCormick said.

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