We red with attention the manuscript of Duan et al. published online on May 26th, 2020 [1]. The authors presented well-described abnormalities of chest computed tomography (CT) findings in 25 SARS-CoV-2-infected patients and suggest positioning this tool. However, we would like to comment on two of their conclusions.
Some COVID-19 patients could initially present with a negative SARS-CoV-2 RT-PCR, but a chest CT evocative of COVID-19. A further respiratory sample is consequently performed with, as reported in their manuscript, a positive RT-PCR result. As written in their manuscript, “Characteristic chest CT imaging features could appear earlier than the viral nucleic acid detection” [1], the authors suggest a superiority of chest CT in comparison to RT-PCR in the early stage of the disease. The first assessments of chest CT showed high performances of the exam from the onset of the symptoms [2]. But, it was reported in the early phase (0–2 days) that 56% of chest CT were normal while 100% of RT-PCR were positive [3]. Indeed, the SARS-CoV-2 viral load is highest during the symptom onset and then trends to decrease with time [4]. Consequently, the diagnostic value of both exams is probably related to epidemiological, clinical, and analytical performances for RT-PCR or diagnostic criteria for chest CT.
False-negative of RT-PCR are not unusual. In order to provide accurate results, the World Health Organization has issued guidelines for SARS-CoV-2 laboratory testing [5]. However, it was suggested the rate of false-negative is higher using RT-PCR assays displaying a single viral target [6, 7]. Nevertheless, false-negative are likely related to preanalytical limitations such as the method of sampling. Indeed, nasopharyngeal swabs are probably more accurate than throat or nasal swabs, but there are more difficult to perform [8, 9]. Furthermore, as SARS-CoV-2 viral load in respiratory sample decrease with the duration of the disease [4], it is likely the patients presenting some days after the onset of the symptoms could display a negative RT-PCR result. Elsewhere, it was suggested upper respiratory tract samples could remain negative in almost exclusive pulmonary diseases [10].
The authors also suggested using “CT and epidemiological history as the primary clues and clinical symptoms and routine laboratory tests as the secondary clues for the early clinical diagnosis of suspicious patients to implement isolation” while awaiting RT-PCR results [1]. However, in our opinion, this strategy is not suitable as chest CT display high specificity but low sensitivity mainly in patients presenting within the first 4 days of the disease [11]. Consequently, some infected-patient would display a chest CT not evocative of COVID-19. Using such a strategy could, therefore, encourage to stop infection prevention and control (IPC) measure before the RT-PCR result was obtained. Finally, generating a contrary effect to what expected and increasing the risk of transmission [12]. Therefore, when RT-PCR is not easily available, we emphasize IPC should be implemented in all suspected patients on the basis of epidemiological, clinical, or radiological findings. These measures should be stopped only when the diagnosis is excluded.
In conclusion, as for numerous infectious diseases, the diagnosis of COVID-19 requires a global analysis based on epidemiological, clinical, and complementary exams. These latters should be interpreted according to their advantages and limitations. As a part of this strategy, chest CT is a mainstay when RT-PCR results could not be provided in less than 24 h or in cases of suspected false-negative of the method. Serological tests, recently made available, have also a place of choice in this context.
Acknowledgements
Members of the SARS-CoV-2 Foch hospital study group: Emilie Catherinot, Colas Tcherakian, Louis-Jean Couderc, Antoine Roux, Sylvie Colin de Verdière, Hélène Salvatore and Charlotte Roy (service de pneumologie et transplantation pulmonaire), Richard Galliot, Charles Cerf, Benjamin Zuber, Mathilde Neuville, and David Cortier (service de réanimation), Morgan Le Guen and Camille Cornet (service d’anesthésie), Marion Lecuru, Emilie Jolly, Laurence Mazaux, Marianne Asso-Bonnet, and Tiffany Pascreau (Service de biologie clinique), Mathilde Roumier, Mathieu Groh, Yoland Schoindre, David Khau, Felix Ackermann, Romain Paule, Antoine Bizard and David Zucman (Service de médecine interne), Philippe Grenier and Anne-Laure Brun (service d’imagerie médicale), Anne Verrat, Marie-Christine Ballester, and Etienne Imhaus (service des urgences).
Compliance with ethical standards
Conflict of interest
The authors declare they have no conflict of interest to declare.
Ethical approval
The manuscript does not involve human participants.
Informed consent
Informed consent was not required.
Footnotes
The members of SARS-CoV-2 Foch hospital study group are listed in “Acknowledgements”.
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Reference
- 1.Duan X, Guo X, Qiang J. A retrospective study of the initial 25 COVID-19 patients in Luoyang China. Jpn J Radiol. 2020 doi: 10.1007/s11604-020-00988-4. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Fang Y, Zhang H, Xie J, et al. Sensitivity of chest CT for COVID-19: comparison to RT-PCR. Radiology. 2020 doi: 10.1148/radiol.2020200432. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Bernheim A, Mei X, Huang M, Yang Y, Fayad ZA, Zhang N, et al. (COVID-19): Relationship to duration of infection. Radiology. 2019 doi: 10.1148/radiol.2020200463. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.He X, Lau EHY, Wu P, et al. Temporal dynamics in viral shedding and transmissibility of COVID-19. Nat Med Nat Res. 2020;1:4. doi: 10.1038/s41591-020-0869-5. [DOI] [PubMed] [Google Scholar]
- 5.World Health Organization. (2020) Laboratory testing for 2019 novel coronavirus (2019-nCoV) in suspected human cases. https://www.who.int/publications/i/item/10665-331501. (Accessed 4 Jun 2020)
- 6.Farfour E, Lesprit P, Visseaux B, et al. The Allplex 2019-nCoV (Seegene) assay: which performances are for SARS-CoV-2 infection diagnosis? Eur J Clin Microbiol Infect Dis. 2020 doi: 10.1007/s10096-020-03930-8.pdf. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Farfour E, Jolly E, Pascreau T, et al. SARS-CoV-2 RT-PCR: at least two viral targets are needed. Infect Dis (Lond) 2020 doi: 10.1080/23744235.2020.1769178. [DOI] [PubMed] [Google Scholar]
- 8.Frazee BW, Rodríguez-Hoces de la Guardia A, Alter H, et al. Accuracy and discomfort of different types of intranasal specimen collection methods for molecular influenza testing in emergency department patients. Ann Emerg Med. 2018;71:509–517. doi: 10.1016/j.annemergmed.2017.09.010. [DOI] [PubMed] [Google Scholar]
- 9.Wang X, Tan L, Wang X, et al. Comparison of nasopharyngeal and oropharyngeal swabs for SARS-CoV-2 detection in 353 patients received tests with both specimens simultaneously. Int J Infect Dis. 2020;94:107–109. doi: 10.1016/j.ijid.2020.04.023. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Farfour E, Picard C, Beaumont L, et al. COVID-19 in lung-transplanted and cystic fibrosis patients: be careful. J Cyst Fibros. 2020;19(3):e16–e17. doi: 10.1016/j.jcf.2020.03.021. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Pan F, Ye T, Sun P, et al. Time course of lung changes on chest CT during recovery from 2019 novel coronavirus (COVID-19) pneumonia. Radiology. 2020 doi: 10.1148/radiol.2020200370. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Farfour E, Ballester M-C, Lecuru M, et al. COVID-19: before stopping specific infection control measures be sure to exclude the diagnosis. J Hosp Infect. 2020 doi: 10.1016/j.jhin.2020.04.021. [DOI] [PMC free article] [PubMed] [Google Scholar]