Beijing, Jul 5 (IANS): Researchers have demonstrated that testing of oropharyngeal secretions (OS) -- secretions from the part of the throat at the back of the mouth -- may reduce the number of false-negative results from nasal swab testing of patients who have seemingly recovered from the disease.

In the study, published in the Journal of Dental Research, a small number of patients that had tested negative through nasopharyngeal swabs were found to be positive through the testing of oropharyngeal secretions.

The study from Huazhong University in China included 75 ready-for-discharge COVID-19 patients who tested negative using two consecutive nucleic acid amplification testing (NAAT) of viral samples retrieved with nasopharyngeal swabs (NPS).

"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," said study lead author Jingzhi Ma from Tongji Medical College of Huazhong University.

Because of detection of potential false-negatives in that cohort, NAAT results of paired OS and NPS samples collected from 50 additional Covid-19 recruits during their recovery stage were used in a second prospective study to compare the diagnostic values of the two viral RNA sampling methods.Oropharyngeal secretions obtained from two of the 75 subjects in the first study yielded positive results for SARS-CoV-2 nucleic acid.

In the second study, OS samples were significantly more sensitive for detection of the virus that NPS samples and missed only 14 per cent of positive cases compared with 59 per cent for the nasopharyngeal swabs samples.

A sampling of OS is a simple procedure that can be performed in any quarantine setting and minimizes contact between healthcare workers and patients, thereby reducing the risk of virus transmission, the researchers said.

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