Number of false positive PCR tests (FOI)

​Request  

From Jersey's first PCR test to today's date:

A

How many tests came back as positive for covid-19, but were later found to have been false positives?

B

Please express this as a percentage of all PCR tests taken.

C

Please provide a table or list showing how many days it took for these false positives to be discovered (eg x number of people isolated for one day after testing positive, before false positive was confirmed, y number of people isolated for two days after testing positive, before false positive was confirmed, z number of people isolated for three days after testing positive, before false positive was confirmed and so on)

D

Please confirm how many people, in total, have been asked to isolate due to being direct contacts of people whose tests were subsequently found to be false positives

Response

A

Two types of tests are currently being used in Jersey: PCR tests and antigen-based tests (Lateral Flow and DiaSorin). Both types of tests ascertain whether a person has Covid-19 at the time.

PCR tests - PCR results that are on the cusp between positive and negative on initial testing are repeated immediately at the laboratory. The first ‘cusp’ result is not released; the second result is released, therefore no false positives are released.  

Antigen-based tests - Antigen testing allows us to test people on a frequent basis. All positive antigen-based tests are followed by a PCR test, in order to confirm a positive Covid case. A person with a positive antigen test is required to isolate pending the result of their PCR test. 

Between 8 February 2021 and 18 March 2021, 12 positive antigen-based tests (three Lateral Flow, nine DiaSorin) have subsequently received a negative PCR result.

This is when the data in relation to this system commenced. Prior to February positive Diasorin tests were not followed with a PCR test.

B

These 12 equate to 0.03% of tests taken between 8 February 2021 and 18 March 2021.

C

D

41 Direct Contacts were identified in relation to the 12 cases of positive antigen-based tests. As soon as the negative PCR result was received, these Direct Contacts were called and were released from isolation.