key: cord-305521-lkou3ycu authors: Michel, W.; Farber, J.; Dilas, M.; Tammer, I.; Baar, J.; Kaasch, A. J. title: A combined oro-nasopharyngeal swab is more sensitive than mouthwash in detecting SARS-CoV-2 by a high-throughput PCR assay date: 2020-09-27 journal: nan DOI: 10.1101/2020.09.25.20201541 sha: doc_id: 305521 cord_uid: lkou3ycu Objectives: The optimal diagnostic specimen to detect SARS-CoV-2 by PCR in the upper respiratory tract is unclear. Mouthwash fluid has been reported as an alternative to nasopharyngeal and oropharyngeal swabs. We compared mouthwash fluid with a combined oro-nasopharyngeal swab regarding test performance. Methods: We tested asymptomatic persons with a previous diagnosis of COVID-19 and their household contacts. First, a mouthwash (gargling for at least 5 sec) with sterile water was performed. Then, with a single flocked swab the back of the throat and subsequently the nasopharynx were sampled. Samples were inactivated and analysed on a Roche cobas 6800 system with the Roche SARS-CoV-2 test. Results: Of 76 persons, 39 (51%) tested positive for SARS-CoV-2 by oro-nasopharyngeal swab. Mouthwash detected 13 (17%) of these infections but did not detect any additional infection. Samples that were positive in both tests, had lower cycle threshold (Ct)-values for oro-nasopharyngeal samples, indicating a higher virus concentration, compared to samples only positive in oro-nasopharyngeal swabs. Conclusions: Mouthwash is not as sensitive as combined oro-nasopharyngeal swab in detecting upper respiratory tract infection. upper respiratory tract is unclear. Mouthwash fluid has been reported as an alternative 23 to nasopharyngeal and oropharyngeal swabs. We compared mouthwash fluid with a 24 combined oro-nasopharyngeal swab regarding test performance. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint for SARS-CoV-2 detection is the nasopharyngeal swab [7], but combined naso-52 oropharyngeal swabs can increase the sensivity of SARS-CoV-2 detection [4] . A meta-53 analysis of different SARS-CoV-2 studies showed the highest detection rates in Expected shortages of swabs led us to assess alternative diagnostic specimens. In 59 this study, we compared test performance when using mouthwash or a combined oro-60 nasopharyngeal swab. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted September 27, 2020. The study was performed according to the principles of the Declaration of Helsinki. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted September 27, 2020. The shortage of swabs that are suitable for PCR diagnostics led us to explore the utility 111 of mouthwash in a controlled study. We found a very low sensitivity of mouthwash 112 (33%), when using oro-nasopharyngeal swabs as comparator. We speculate that this 113 striking difference in sensitivity is partly due to the dilution of the mouthwash sample. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted September 27, 2020. The only published study reported that the rate of positivity for SARS-CoV-2 was higher 117 in self-collected throat washings with sterile normal saline than in nasopharyngeal 118 swabs [10] . However, the small sample size of eleven patients does not allow firm 119 conclusions. Our study has also limitations. Mouthwash with gargling was performed as a self-137 administered procedure and we observed some variation in adherence to the protocol 138 regarding the duration and intensity of gargling, which may have influenced the results. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted September 27, 2020. . https://doi.org/10.1101/2020.09.25.20201541 doi: medRxiv preprint 7 There is a high likelihood of aerosol formation during gargling. Thus, mouthwash 143 should be performed alone in a well-ventilated area. This may limit its use in patients 144 to minimize exposure of health-care personel.In conclusion, SARS-CoV2 detection 145 with mouthwash showed a low sensitivity compared to oro-nasopharyngeal swabs. Thus, we do not recommend mouthwash performing combined oro-nasopharyngeal 147 swabs, especially in patients with no or mild symptoms. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted September 27, 2020. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted September 27, 2020. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted September 27, 2020. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted September 27, 2020. . https://doi.org/10.1101/2020.09.25.20201541 doi: medRxiv preprint A Novel Coronavirus from Patients with 167 Pneumonia in China Coronaviruses and SARS-CoV-2: A Brief Overview Brief: Transmission of SARS-CoV-2: implications for infection 172 prevention precautions Laboratory testing of SARS-CoV, MERS-CoV, and 176 SARS-CoV-2 (2019-nCoV): Current status, challenges, and countermeasures Isolation of infectious SARS-CoV-2 from urine of a 179 COVID-19 patient Prolonged presence of SARS-CoV-2 viral RNA in 182 faecal samples Laboratory testing for 2019 185 novel coronavirus (2019-nCoV) in suspected human cases SARS-CoV-2 Detection 190 in Different Respiratory Sites: A Systematic Review and Meta-Analysis Differences of Severe Acute Respiratory 194 Syndrome Coronavirus 2 Shedding Duration in Sputum and Nasopharyngeal 195 Swab Specimens Among Adult Inpatients With Coronavirus Disease Effect of throat washings on detection of 199 2019 novel coronavirus Detection of SARS-CoV-2 in Different 202 Types of Clinical Specimens A 205 combination of naso-and oropharyngeal swabs improves the diagnostic yield 206 of respiratory viruses in adult emergency department patients Upper respiratory tract 209 sampling in COVID-19 It is made available under a perpetuity.is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprintThe copyright holder for this this version posted September 27, 2020.