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Tags Current Affairs

Reducing false negatives

Date: 05 July 2020 Tags: Miscellaneous


Researchers have reported that testing of oropharyngeal secretions from the part of the throat at the back of the mouth may reduce the number of false-negative results.



False negatives, when a person carrying a pathogen test negative, have been reported several times during the Covid-19 pandemic. 



  • A small number of patients who had tested negative through nasal swabs were found to be positive through the testing of oropharyngeal secretions.

  • The study included 75 ready-for-discharge Covid-19 patients who tested negative using nasal swabs. Because of the detection of potential false-negatives in that cohort, a second study paired oropharyngeal and nasopharyngeal samples collected from 50 additional Covid-19 recruits during their recovery stage.

  • Oropharyngeal secretions obtained from subjects in the first study yielded positive results for SARS-CoV-2. In the second study, oropharyngeal samples missed only 14% of positive cases, compared with 59% for the nasal samples.

  • A sampling of oropharyngeal secretions is a simple procedure that can be performed in any quarantine setting. It minimises contact between healthcare workers and patients, thereby reducing the risk of virus transmission.

  • The NPS test has a risk of sending home more patients who still have the infection while the OS test will make such errors in fewer patients.

  • Although OS sampling improves the accuracy of SARS-CoV-2 nucleic acid testing, it must be emphasised that this conclusion is based on very small sample size.

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