Diagnosis of COVID-19.

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Diagnosis of COVID-19.

 

The possibility of COVID-19 acquisition should be taken in consideration in ptns with compatible symptomatology, particularly fever and/or the related respiratory tract Sms, who’re resident in or have traveled to the well-known zones with community transmission or who have had a recent close contact with a confirmed/suspected case of COVID-19. Physicians should be aware of the possibility of COVID-19 in ptns with severe respiratory illness whenever other etiology is lacking. Whenever possible, all symptomatizing ptns with suspected COVID-19 should proceed to testing for severe acute respiratory syndromes coronavirus 2 (SARS-CoV-2). However, limitations in testing capacity may impede testing all suspected ptns; priority in testing may include:

1)    Hospitalized ptns & symptomatizing subjects e.g. health care workers or

2)    First responders,

3)    Work/reside in congregate living settings, or

4)    Presence of risk factors with severe comorbidities.  

-       Nucleic acid amplification testing (NAAT), most commonly with a reverse-transcription polymerase chain reaction (RT-PCR) assay, to detect SARS-CoV-2 RNA from the upper respiratory tract is the preferred initial diagnostic test for COVID-19. Sometimes, Ag testing may be the initial applied test, but the sensitivity of Ag testing is below that of NAATs, and negative Ag testing needs to be confirmed with NAAT.  

 

A +ve NAAT for SARS-CoV-2 confirms the Dgx of COVID-19. For many symptomatic individuals, a single negative NAAT testing is enough to exclude the   COVID-19 Dgx.

However, if initial tests are negative but the suspicion of COVID-19 remains high and confirming the presence of infection is important for management or infection control, we can repeat testing. In some circumstances, NAAT on lower respiratory tract specimen (for hospitalized ptns showing an evidence of lower respiratory tract illness) or serology (for symptomatizing ptns for at least couple of weeks) may be a helpful diagnostic test.

Indications for testing asymptomatic subjects may include:

1)    Close contact with an infected ptn with COVID-19,

2)    Screening study in congregate settings (e.g, long-term care facility, correctional & detention facility, homeless shelters), and

3)    Screening of hospitalized ptns in high-prevalence zones.

-       We suggest that post-exposure testing be done 5-7 d. after exposure, despite that the optimal timing still uncertain.

 

NAATs detect SARS-CoV-2 RNA in ptn specimen and are highly specific. Despite they can detect low levels of viral RNA, the clinical sensitivity of these tests is likely affected by:

1)    Type & quality of the provided specimen,

2)    Duration of illness within testing,

3)    Assay specifity.

False-negative rate have ranged from < 5-40 %. Serologic testing that detect AB to SARS-CoV-2 in the blood and can help identify ptns who’re previously acquitted COVID-19. Detectable AB generally take several days to weeks to develop; thus, serologic tests hv less utility for Dgx in acute setting. Serologic testing should be interpreted cautiously owing to variable performances among variable assays, potential for low positive predictive value in case of low seroprevalence, and uncertain serologic correlates of immunity. In case COVID-19 disease suspicion, infection control measures should be applied. Interim guidance has been provided by the WHO and by the US Centers for Disease Control and Prevention (CDC), in addition to other expert institutes.

 

REFERENCES

1.    World Health Organization. Director-General's remarks at the media briefing on 2019-nCoV on 11 February 2020. http://www.who.int/dg/speeches/detail/who-director-general-s-remarks-at-the-media-briefing-on-2019-ncov-on-11-february-2020 (Accessed on February 12, 2020).

2.    Centers for Disease Control and Prevention. 2019 Novel coronavirus, Wuhan, China. Information for Healthcare Professionals. https://www.cdc.gov/coronavirus/2019-nCoV/hcp/index.html (Accessed on February 14, 2020).

3.    World Health Organization. Novel Coronavirus (2019-nCoV) technical guidance. https://www.who.int/emergencies/diseases/novel-coronavirus-2019/technical-guidance (Accessed on February 14, 2020).

4.    Struyf T, Deeks JJ, Dinnes J, et al. Signs and symptoms to determine if a patient presenting in primary care or hospital outpatient settings has COVID-19 disease. Cochrane Database Syst Rev 2020; 7:CD013665.

5.    Cohen PA, Hall LE, John JN, Rapoport AB. The Early Natural History of SARS-CoV-2 Infection: Clinical Observations From an Urban, Ambulatory COVID-19 Clinic. Mayo Clin Proc 2020; 95:1124.

6.    Tostmann A, Bradley J, Bousema T, et al. Strong associations and moderate predictive value of early symptoms for SARS-CoV-2 test positivity among healthcare workers, the Netherlands, March 2020. Euro Surveill 2020; 25.

7.    Makaronidis J, Mok J, Balogun N, et al. Seroprevalence of SARS-CoV-2 antibodies in people with an acute loss in their sense of smell and/or taste in a community-based population in London, UK: An observational cohort study. PLoS Med 2020; 17:e1003358.

8.    Infectious Diseases Society of America. COVID-19 Prioritization of Diagnostic Testing. https://www.idsociety.org/globalassets/idsa/public-health/covid-19-prioritization-of-dx-testing.pdf (Accessed on March 22, 2020).

9.    Centers for Disease Control and Prevention. Overview of Testing for SARS-CoV-2. https://www.cdc.gov/coronavirus/2019-ncov/hcp/testing-overview.html (Accessed on September 21, 2020).

10.  Infectious Diseases Society of America Guidelines on the Diagnosis of COVID-19, May 5, 2020. https://www.idsociety.org/practice-guideline/covid-19-guideline-diagnostics/ (Accessed on May 07, 2020).