Coronavirus outbreak: Study says testing of throat secretions reduces false negatives

Wuhan, July 04: In several occasions, false negatives have been reported during the testing of COVID-19 in the ongoing pandemic. These results have come up during nasal swab testing of patients who have seemingly recovered from the disease. But, these patiests have later been found to be still carrying the novel coronavirus.

With these false negatives ringing the alarm bells, researchers have reported that testing of oropharyngeal secretions (a secretion from the part of the throat at the back of the mouth) may reduce the number of false negative results. The researchers have published their findings in the Journal of Dental Research.

This study was led by Jingzhi Ma of Tongji Medical College, Wuhan. According to the study, a group of patients who had tested negative through nasal swabs were found to be positive through the testing of oropharyngeal secretions.

As many as 75 ready-for-discharge COVID-19 patients who tested negative using nasal swabs were part of the study. A second study paired oropharyngeal and nasopharyngeal samples collected from 50 additional COVID-19 recruits during their recovery stage.

Oropharyngeal secretions obtained from 2 of the 75 subjects in the first study yielded positive results for the deadly virus. In the second study, oropharyngeal samples missed only 14 per cent of positive cases, compared with 59 per cent for the nasal samples, the study said.

The study further said that sampling of oropharyngeal secretions is a simple procedure that can be performed in any quarantine setting. This secretion also minimises contact between healthcare workers and patients, thereby reducing the risk of virus transmission.

In a statement, Jingzhi Ma said, "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 a very small sample size."