Gargle Lavage as a Safe and Sensitive Alternative to Swab Samples to Diagnose COVID-19: A Case Report in Japan

To the Editor—The diagnosis of coronavirus disease 2019 (COVID-19) requires upper or lower respiratory samples. However, the problem of COVID-19 is that around 70%–80% of patients do not have productive cough [1]. To protect healthcare workers during sampling for diagnosis, the US Centers for Disease Control and Prevention recommends not inducing cough to collect sputum samples, but rather the collection of nasopharyngeal and/or oropharyngeal swabs, or nasopharyngeal wash/aspirate or nasal aspirate. Nasal swabs are reported to have higher viral titers than throat swabs [2]; accordingly, nasopharyngeal swabs are the preferred samples in Japan. However, nasopharyngeal and oropharyngeal swabs cause discomfort to patients and can potentially increase the risk of direct exposure of healthcare workers by provoking coughing. Moreover, the sensitivity for virus detection is low with these swabs; viral load is reportedly higher in sputum samples [3].

Here we report a case in which gargle lavage samples yielded a positive polymerase chain reaction (PCR) result. A 55-year-old man came to our hospital complaining of 5 days of fever (maximum 38.6°C). He had a mild headache, but no respiratory symptoms. Four days prior to his fever, he had had contact with a COVID-19 infection cluster. On admission, his vital signs were within the normal range and his breathing sounds were normal. His blood tests on admission (day 6) revealed mild lymphocytopenia (720 cells/μL) and slightly elevated C-reactive protein (0.88 mg/dL). Although his chest radiograph was not remarkable, his computed tomographic scan revealed patchy ground-glass opacities predominantly in the left lower lobe (Supplementary Figures 1 and 2). Samples were taken to test for COVID-19 by real-time reverse-transcription PCR, using primers recommended by the Chinese Center for Disease Control and Prevention [4]. Oropharyngeal swabs and gargle lavage (using 10 mL of normal saline) were collected because he did not produce sputum. Additional gargle lavage samples and oropharyngeal swabs were collected and tested on days 8 and 9 and found to be positive, with a slightly higher amount of viral genome in the gargle lavage sample (Supplementary Figure 3). His PCR became negative on day 16 and 19, and he was discharged on day 19.

For other respiratory pathogens, gargle lavage samples have been reported to be more sensitive than throat swabs [5]. Gargle lavage can be done by patients themselves without putting healthcare professionals at increased risk, which is reportedly high in this outbreak [1]. Gargle lavage thus offers a safer and possibly more sensitive alternative or additional option for diagnosing COVID-19.

Supplementary Data

Supplementary materials are available at Clinical Infectious Diseases online. Consisting of data provided by the authors to benefit the reader, the posted materials are not copyedited and are the sole responsibility of the authors, so questions or comments should be addressed to the corresponding author.

Notes

Author contributions. M. S. and E. A. collected the clinical samples and were responsible for the clinical management of the patient. S. Y., M. K., K. I.-H., and Y. K. facilitated and conducted the laboratory work. H. Y. provided overall supervision. M. S. drafted the manuscript. All authors revised the drafts and approved the final manuscript.

Acknowledgments. Ethics approval was granted by the ethics board of the Institute of Medical Science, University of Tokyo (2019-71-0201). The patient provided written consent for publication.

Financial support. This study was funded by the Japan Agency for Medical Research and Development (grant number 19fk0108113h0001) and by the National Institute of Allergy and Infectious Diseases–funded Center for Research on Influenza Pathogenesis (contract number HHSN272201400008C).

Potential conflicts of interest. Y. K. is a cofounder of FluGen, which is now developing a COVID-19 vaccine. All other authors report no potential conflicts of interest. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.