Laboratory diagnosis of emerging human coronavirus infections – the state of the art

Original Article: Michael J. Loeffelholz and Yi-Wei Tang, Laboratory diagnosis of emerging human coronavirus infections – the state of the art, Emerging Microbes & Infections

Author of summary: Alessia Villois; Reviewer: Bernadette Basilico

Original Article Published on March 30th, 2020

The three unprecedented outbreaks of HCoVs infections have highlighted the importance of suitable diagnostic methods. This article reviews the recommended sample types, the current analysis techniques and the future directions. Nasopharyngeal swab is usually the preferred collection method and deeper specimens are sometimes obtained by bronchoscopy. PCR-based techniques are used for diagnosis and current research efforts focus on having faster, safer and simpler tests for COVID19.

HCoVs diseases

Coronaviruses are found in both animals and humans. In particular, human coronaviruses (HCoVs) are endemic or epidemic (SARS-CoV, MERS-CoV, SARS-CoV-2).

Patients with SARS-CoV infection often have an incubation of 4-5 days, followed by fever, headache and myalgia. Respiratory symptoms usually develop 1 week after the illness onset. Pneumonia and respiratory deterioration occurs in 20-30% of the cases (the percentage is even higher for MERS). SARS-CoV-2 causes probably a similar clinical course, but is substantially more contagious than SARS-CoV. Mortality rate varies widely and depends on age, risk factors and the denominator definition (hospitalized cases, all symptomatic cases etc.), but it is estimated to be <2% globally.

Sample collection for laboratory diagnosis

For sensitive detection of SARS-CoV, MERS-CoV and SARS-CoV-2, it is recommended to collect both upper [oropharyngeal (OP) and nasopharyngeal (NP)] and lower respiratory tract samples [sputum, bronchoalveolar lavage fluid (BAL)]. The NP sample is more reliable than the OP one, therefore if the latter is collected, it should be combined with the first one. The samples collected from lower respiratory tracts are useful because the initial stage of infection may not be detected by the nasopharyngeal samples. However, the collection of sputum and BAL via bronchoscopy poses biosafety risks to healthcare workers due to the creation of aerosol droplets. Therefore, as an alternative, repeated NP testing can be used to increase the likelihood of detecting SARS-CoV-2.

Saliva collection is also a promising non-invasive method for the diagnosis and course monitoring of SARS-COV-2 infection.

Testing methods

  • Routine detection of SARS-CoV-2 is achieved mostly by PCR. Several protocols are available and specimen types include upper and lower respiratory samples. In China, by the time of writing, 11 molecular devices had received approval by NMPA, 9 of which based on real-time PCR.
  • Rapid antigen tests would theoretically provide fast and low-cost detection of HCoVs, but they might be poorly sensitive, based on the experience with influenza. However, a lateral-flow test is under development by Sona Nanotech, aimed at screening COVID19 patients and produce results in 5-15 minutes.
  • Serology assays are not routinely used for diagnostics, due to the lack of commercial reagents, but they are important in understanding the epidemiology of SARS-CoV-2 (evaluate the extent of asymptomatic infections, retrospective antibody detection to assess if people developed an immune response).  They can also be used as supplementary diagnostic tools, when a NP swab specimen was not collected appropriately and the molecular assays were performed unsatisfactorily. In China, 6 serology devices have received urgent approval by NMPA by 12 March 2020.
  • Isolation of HCoVs in cell culture is not routinely performed for diagnostics, but it is critical to support the development of vaccines and therapeutic agents.

In conclusion, current diagnostic tests for SARS-CoV-2 and the other HCoVs are mainly based on molecular methods, while a few tests are based on antigen or antibody detection. Most of the effort is concentrated in decreasing the analysis time, reducing the biosafety risk, increase simplicity and portability of the devices.

Be the first to comment on "Laboratory diagnosis of emerging human coronavirus infections – the state of the art"

Leave a comment

Your email address will not be published.