A new study has found that testing of secretions from the mouth and pharynx of a person may reduce the number of false negative results from nasal swab tests of patients who have seemingly recovered from the disease.
The study has been published in the Journal of Dental Research. The study said that a small number of patients that had tested negative for COVID-19 through nasopharyngeal swabs (NPS) were found to be positive through the testing of oropharyngeal secretions.
It included 75 ready-for-discharge coronavirus patients who tested negative using two consecutive nucleic acid amplification testing (NAAT) of viral samples retrieved with NPS, according to the researchers from Huazhong University of Science and Technology, China.
Because of the detection of potential false-negatives in that cohort, NAAT results of paired OS and NPS samples collected from 50 additional coronavirus 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, the researchers said. In the second study, OS samples were significantly more sensitive for detection of the virus than NPS samples, and missed only 14 per cent of positive cases compared with 59 per cent for the NPS samples. A sampling of OS is a simple procedure that can be performed in any quarantine setting and 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,” said Jingzhi Ma, from Huazhong University of Science and Technology. “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,” said Ma.