On the same day that we witnessed the swearing in of Joe Biden as President of the United States, the World Health Organization published a notice to SARS-CoV-2 testing laboratories and administers that “careful interpretation of weak positive test results is needed.”

The notice, dated January 13th, but published today, suggests that labs and testing administers are presently failing to correctly interpret PCR test results for SARS-CoV-2.

literally one hour after Biden takes the oath, the WHO admits that PCR testing at high amplification rates alters the predictive value of the tests and results in a huge number of false positives pic.twitter.com/iDtXmappRw

— Andy Swan (@AndySwan) January 20, 2021

The WHO notice specifically points to the cycle threshold values that labs use when performing the PCR tests. Cycle thresholds can be amplified to values where even dead viral material can be detected, resulting in false positives.

Florida has been ahead of the curve in monitoring the cycle threshold value they accept from labs. In a memorandum released on December 3, 2020, Florida Governor Ron DeSantis required all testing labs report their amplification cycle threshold on each PCR test.

In a “corrected proof” for the Infections Diseases Society of America, testing data shows that positive test results found at a cycle threshold value of 35 have a 97% chance of being a false positive. A cycle threshold value of 25 results in only 30% false positives, indicating that the higher the cycle threshold value, the less accurate the SARS-CoV-2 tests become.

Missoula County Health Department relies almost exclusively on PCR tests for its SARS-CoV-2 “surveillance regimen” due to “supply chain shortages” on rapid tests. However, “by several criteria […] (PCR) test fails when used in a surveillance regimen,” according to a report by three physicians published in the New England Journal of Medicine. This is due to inconsistent cycle threshold standards and the 1-2 days it takes to receive a result back.

In order to lift local mask mandates and restrictions on individuals and businesses, the Missoula County Health Board has set a caseload upper limit of 25 positive SARS-CoV-2 cases per 100,000 individuals over a 7-day period. The county has also set a policy of only testing people with symptoms. The intuitive result of restricting the sample to people already presenting symptoms is a higher positivity rate.

A true determination of the prevalence of SARS-CoV-2 in the population would require the county to implement rapid testing rather than PCR testing and to make testing more generally available. Rapid testing is only available at one testing site on Flynn Lane and no indications have been made that rapid testing is expanding.

We asked Missoula County Health Department Lead Public Information Officer Hayley Devlin if the health department knows the cycle threshold the labs use for their SARS-CoV-2 tests and if the health department maintains its own cycle threshold standard. We will update readers if and when the county responds.

Update (01/21/2021 10:59am): The Missoula County Health Department declined to provide an answer instead deferring to Missoula County communications coordinator Allison Franz. “You can email Allison Franz to submit a request for that info,” the health department stated. We have submitted an additional request for PCR cycle thresholds for SARS-CoV-2 tests performed in Missoula County. We will update readers when Allison responds.

Update (01/26/2021 10:49am): Liaison Officer Stephen Robertson responded to a Montana Public Records Act request we made for communications associated with the County’s COVID-19 response. Robertson asked for a phone call. We asked that we continue correspondence via email and to, “Please also include data that specifies the PCR cycle threshold values used in lab tests for the SARS-CoV-2 PCR tests.”

Update (01/29/2021 1:19pm): Liaison Officer Stephen Robertson indicated that the county is not aware of the PCR cycle threshold values used in their own SARS-CoV-2 PCR tests. We emailed for clarification.

Update (02/04/2021 12:24pm): We replied to Liaison Officer Stephen Robertson asking for an update to the Montana Public Records Act request for PCR threshold cycle value information for SARS-CoV-2 tests performed and accepted by the county. We CC’d the Missoula City Council and the Missoula County Commissioners.