Diagnosis of SARS-CoV-2 infection based on CT scan vs RT-PCR: reflecting on experience from MERS-CoV

  • J.A. Al-Tawfiq
    Correspondence
    Corresponding author. Address: P.O. Box 76, Room A-428-2, Building 61, Dhahran Health Centre, Johns Hopkins Aramco Healthcare, Dhahran 31311, Saudi Arabia. Tel.: +966 13 870 3524; fax: +966 13 870 3790.
    Affiliations
    Infectious Disease Unit, Specialty Internal Medicine, Johns Hopkins Aramco Healthcare, Dhahran, Saudi Arabia

    Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA

    Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
    Search for articles by this author
  • Z.A. Memish
    Affiliations
    Research Centre, King Saud Medical City, Ministry of Health, Riyadh, Saudi Arabia

    Al-Faisal University, Riyadh, Saudi Arabia

    Hubert Department of Global Health, Rollins School of Public Health, Emory University, Atlanta, GA, USA
    Search for articles by this author
Published:March 05, 2020DOI:https://doi.org/10.1016/j.jhin.2020.03.001
      As of 29th February 2020, the World Health Organization had reported a total of 83,652 cases of coronavirus disease 2019 (COVID-19) in 51 countries in addition to China [
      • World Health Organization
      Situation Report 17. Situation in numbers: total and new cases in last 24 hours.
      ]. The diagnosis of respiratory viruses such as Middle East respiratory syndrome coronavirus (MERS-CoV) and severe acute respiratory syndrome coronavirus (SARS-CoV) relies on detection of the virus by real-time reverse transcriptase polymerase chain reaction (rRT-PCR) for in-vitro qualitative detection. The current recommendations are likewise to use rRT-PCR for the detection of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in respiratory samples. There are many knowledge gaps facing the global health community in dealing with the new emerging SARS-CoV-2. Among the most pertinent is early identification of cases to facilitate application of isolation policies. The currently available RT-PCR kits are variable, offering sensitivities ranging between 45% and 60%; thus, particularly early in the course of an infection, repeat testing may be required to make a diagnosis. This is not easy to apply with the global shortage of testing kits. This mirrors experience with MERS-CoV. In a study of 336 patients with MERS, 89% had a positive result after one swab, 96.5% had a positive result after two swabs, and 97.6% had a positive result after three swabs (Figure 1) [
      • Alfaraj S.H.
      • Al-Tawfiq J.A.
      • Memish Z.A.
      Middle East respiratory syndrome coronavirus intermittent positive cases: implications for infection control.
      ]. China has changed the case definition over the last 2 months to improve the ability to detect new cases. Data have emerged on the value of computed tomography (CT) scanning of the chest in the early diagnosis of cases. Multiple reports published to date have revealed higher sensitivity of chest CT in early detection of cases of SARS-CoV-2 [
      • Ai T.
      • Yang Z.
      • Hou H.
      • Zhan C.
      • Chen C.
      • Lv W.
      • et al.
      Correlation of chest CT and RT-PCR testing in coronavirus disease 2019 (COVID-19) in China: a report of 1014 cases.
      ]. In a study of 51 patients, the positivity rate for a single respiratory swab was 70%, an additional 24% (94% cumulative) after a second test, and an additional 3.9% (98% cumulative) after a third test (Figure 1) [
      • Fang Y.
      • Zhang H.
      • Xie J.
      • Lin M.
      • Ying L.
      • Pang P.
      • et al.
      Sensitivity of chest CT for COVID-19: comparison to RT-PCR.
      ]. However, abnormal CT scan findings compatible with viral pneumonia were seen in 98% of patients [
      • Fang Y.
      • Zhang H.
      • Xie J.
      • Lin M.
      • Ying L.
      • Pang P.
      • et al.
      Sensitivity of chest CT for COVID-19: comparison to RT-PCR.
      ]. This difference resulted in the study authors stating that CT scan is more sensitive than PCR. Reasons for the low sensitivity of PCR may include insensitive nucleic acid detection methods, variations in the accuracies of different tests, low initial viral load or improper clinical sampling [
      • Fang Y.
      • Zhang H.
      • Xie J.
      • Lin M.
      • Ying L.
      • Pang P.
      • et al.
      Sensitivity of chest CT for COVID-19: comparison to RT-PCR.
      ]. An additional reason may be that lower respiratory samples may be better than upper respiratory samples, as is the case with MERS-CoV [
      • Memish Z.A.Z.A.
      • Al-Tawfiq J.A.J.A.
      • Makhdoom H.Q.H.Q.
      • Assiri A.
      • Alhakeem R.F.R.F.
      • Albarrak A.
      • et al.
      Respiratory tract samples, viral load, and genome fraction yield in patients with Middle East respiratory syndrome.
      ,
      • Corman V.M.
      • Albarrak A.M.
      • Omrani A.S.
      • Albarrak M.M.
      • Farah M.E.
      • Almasri M.
      • et al.
      Viral shedding and antibody response in 37 patients with Middle East respiratory syndrome coronavirus infection.
      ].
      Figure 1
      Figure 1Cumulative positive rate of swabs for the diagnosis of severe acute respiratory syndrome coronavirus-2 (light green bars) and Middle East respiratory syndrome coronavirus (dark green bars) based on reverse transcriptase polymerase chain reaction.

      Keywords

      To read this article in full you will need to make a payment

      Subscribe:

      Subscribe to Journal of Hospital Infection
      Already a print subscriber? Claim online access
      Already an online subscriber? Sign in
      Institutional Access: Sign in to ScienceDirect

      References

        • World Health Organization
        Situation Report 17. Situation in numbers: total and new cases in last 24 hours.
        WHO, Geneva2020 (Available at:)
        • Alfaraj S.H.
        • Al-Tawfiq J.A.
        • Memish Z.A.
        Middle East respiratory syndrome coronavirus intermittent positive cases: implications for infection control.
        Am J Infect Control. 2019; 47: 290-293
        • Ai T.
        • Yang Z.
        • Hou H.
        • Zhan C.
        • Chen C.
        • Lv W.
        • et al.
        Correlation of chest CT and RT-PCR testing in coronavirus disease 2019 (COVID-19) in China: a report of 1014 cases.
        Radiology. 2020; : 200642https://doi.org/10.1148/radiol.2020200642
        • Fang Y.
        • Zhang H.
        • Xie J.
        • Lin M.
        • Ying L.
        • Pang P.
        • et al.
        Sensitivity of chest CT for COVID-19: comparison to RT-PCR.
        Radiology. 2020; : 200432https://doi.org/10.1148/radiol.2020200432
        • Memish Z.A.Z.A.
        • Al-Tawfiq J.A.J.A.
        • Makhdoom H.Q.H.Q.
        • Assiri A.
        • Alhakeem R.F.R.F.
        • Albarrak A.
        • et al.
        Respiratory tract samples, viral load, and genome fraction yield in patients with Middle East respiratory syndrome.
        J Infect Dis. 2014; 210: 1590-1594
        • Corman V.M.
        • Albarrak A.M.
        • Omrani A.S.
        • Albarrak M.M.
        • Farah M.E.
        • Almasri M.
        • et al.
        Viral shedding and antibody response in 37 patients with Middle East respiratory syndrome coronavirus infection.
        Clin Infect Dis. 2016; 62: 477-483
        • Xie X.
        • Zhong Z.
        • Zhao W.
        • Zheng C.
        • Wang F.
        • Liu J.
        Chest CT for typical 2019-nCoV pneumonia: relationship to negative RT-PCR testing.
        Radiology. 2020; : 200343https://doi.org/10.1148/radiol.2020200343
        • Wei M.
        • Yuan J.
        • Liu Y.
        • Fu T.
        • Yu X.
        • Zhang Z.-J.
        Novel coronavirus infection in hospitalized infants under 1 year of age in China.
        JAMA. 2020; https://doi.org/10.1001/jama.2020.2131
        • Wang Y.
        • Kang H.
        • Liu X.
        • Tong Z.
        Combination of RT-qPCR testing and clinical features for diagnosis of COVID-19 facilitates management of SARS-CoV-2 outbreak.
        J Med Virol. 2020; https://doi.org/10.1002/jmv.25721
        • Zou L.
        • Ruan F.
        • Huang M.
        • Liang L.
        • Huang H.
        • Hong Z.
        • et al.
        SARS-CoV-2 viral load in upper respiratory specimens of infected patients.
        N Engl J Med. 2020; : 2001737https://doi.org/10.1056/NEJMc2001737