Reliability of induced sputum test is greater than that of throat swab test for detecting SARS-CoV-2 in patients with COVID-19: A multi-center cross-sectional study

ABSTRACT

We previously reported that sputum induction was more sensitive than throat swabs for the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in two convalescent coronavirus disease 2019 (COVID-19) patients; however, the value and safety of induced sputum testing require further study. We conducted a prospective multi-center cross-sectional study to compare induced sputum to throat swabs for SARS-CoV-2 detection. Confirmed COVID-19 patients from six hospitals in six cities across China who received one or more negative RT-PCR result for SARS-CoV-2 were enrolled, and paired specimens (induced sputum and throat swabs; 56 cases) were assayed. In three paired samples, both the induced sputum and throat swabs were positive for SARS-CoV-2. The positive rate for induced sputum was significantly higher than for throat swabs both overall (28.6% vs 5.4%, respectively; p < 0.01). Patients were divided according to time span from onset of illness to sample collection into the more-than-30-day (n = 26) and less-than-30-day (n = 30) groups. The positive rate for induced sputum was also significantly higher than for throat swabs in the less-than-30-day group (53.3% vs 10.0%, respectively; p < 0.001). For the more-than-30-day group, all paired samples were negative for SARS-CoV-2. Blood oxygen saturation, respiratory rate, and heart rate remained stable during sputum induction and no staff were infected. Because induced sputum is more reliable and has a lower false-negative rate than throat swabs, we believe induced sputum is more useful for the confirmation of COVID-19 and is safer as a criterion for release from quarantine.

KEYWORDS:

• COVID-19
• reliability
• induced sputum
• throat swab
• SARS-CoV-2

Acknowledgments

This work is funded by Clinical Research Project of Affiliated Hospital of Guangdong Medical University and Guangdong Basic and Applied Basic Research Foundation (2020B1515020004, 2018A0303130269). The authors would like to thank all the patients involved in this study.

Author contributions

HQH provided the concept and conducted the study. HQH, TWL, FFX, JFZ, YZH, LPJ, HC performed the research. HQH and TWL wrote the manuscript. JYW was responsible for statistical review. All authors contributed to data acquisition, data analysis, or data interpretation, and approved the final version.

Ethical approval and consent to participate

The study was approved by the ethics committee of the Affiliated Hospital of Guangdong Medical University (approval no. PJ2020-013). Informed and written consent was obtained from all participating subjects in accordance with the guidelines of the Declaration of Helsinki.

Disclosure statement

We declare no competing interests.

Additional information

Funding

This work is funded by Clinical Research Project of Affiliated Hospital of Guangdong Medical University and Guangdong Basic and Applied Basic Research Foundation [2020B1515020004, 2018A0303130269].