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Rapid-Test cross-reactions

Dear Expert-team,
in schools Rapid-Testing with Antigen-Tests for Sars-CoV2 is startings. Due to cross-reactions there can be false positive results. Cross-reactions with bacteria and viruses are listed, that are frequently found in CF.
Do CF patients have to expect false positive test results? Are there tests that are more suitable, so that one can find a test suitable for the individual colonizations with germs?
Many thanks,
Dear questioner,
the usage of antigen-rapid-tests for identification of a SARS-CoV2-infection is at the moment discussed intensively and partly also controversially. SARS-CoV-2 antigen-rapid tests are without doubt inferior concerning sensitiviy and specificity compared to the PCR test.
On the homepage of the German institute for drugs and medical products at the moment 250 tests systems from different companies are listed. About 100 tests have been evaluated by the paul-Ehrlich-Institute concerning their sensitivity (date 1.4.2021) and have been judged to be in the frame of the technical standard (i.e. a certain percentage of right positive samples is given). The specificity however, is the percentage of persons who are not infected that are judged to be healthy by the test. A test with a sepcificity of 97% gives in 3 of 100 people a false-positive result. Both values depend on each other. False positive results can have different reasons and can be due e.g. to cross-reactions with other antigens. False-positive results do obviously also occur, if S. aureus-positive nasal swabs are used as sample-matrix. Positive results have thererfore been checked by PCR, in order to avoid an unnecessary uncertainty and unjustified quarantine.
One could probably assume, that in case of persons with CF and a higher prevalence for S. aureus false-positive reuslts could be more frequent. At the moment there are no systematic test on the specificity and/or cross-reactions dependent on certain underlying diseases, like CF. Therefore it is impossible to give a recommendation for or against a certain test concering this question.
Best regards,
Dr. M. Hogardt