COVID-19 crash course

Laboratorium-diagnostiekKatrien Lagrou

Virological assessment of hospitalized patients with COVID-19

• 9 cases were enrolled because of infection upon close contact to an index case, all mild courses

• Diagnosis by RT-PCR from oro-or nasopharyngeal swab, earliest swab taken on day 1 of symptoms (often mild or prodromal)

• All treated in hospital in Munich

R. Wölfel et al Nature 2020 Apr 1

R. Wölfel et al Nature 2020 Apr 1

No difference viral loads or detection rates naso- versus oropharyngeal swabs• day 1-5: all swabs positive• > day 5: detection rate 40%

INFECTIVITY RESPIRATORY TRACT

Virus isolation• first week: 17% swabs, 83% sputum

samples: isolation successful• >8 days: no isolates obtained despite

high viral loads

Viral sgRNA• only transcribed in infected cells, not

packaged into virions - indicator of actively-infected cells

• only detected during first 5 days in throat swabs

STOOL SAMPLES

• High viral loads• No or only minimal replication in stool

(sgRNA)• Virus isolation never successful

ANTIBODY RESPONSE

• seroconversion in 50% by day 7 and 100% by day 14

• all patients detectable neutralizing antibodies

URINE or SERUM samples: no detection of viral RNA

R. Wölfel et al Nature 2020 Apr 1

R. Wölfel et al Nature 2020 Apr 1

SARS-CoV-2 Viral load kinetics: throat versus nasal swabs

L. Zou et al. NEJM 2020, March 19

• 18 patients (Guangdong, China), 14 returned from Wuhan

• 1 asymptomatic patient: similar viral loads, CT scan unremarkable

mid-turbinate and nasopharynx

Posterior oropharyngeal saliva samples: an alternative?

KK. To et al. Lancet Infect Dis 2020 Mar 23

Observational cohort study: two hospitals Hong Kong

23 patients: • 10 severe disease• 17 (74%) ground-glass opacities on CT• 3 patients intubated (endotracheal

aspirate)

Self collected samplesPatients were asked to produce an early morning saliva sample from the throat, i.e. coughed up by clearing the throat

PCR testing• Nasopharyngeal swabs preferred, more data needed for comparison

with throat swabs or other alternatives• (Rapid) decline of viral load in upper respiratory tract samples during

first week after start symptoms, timing of sampling likely affects sensitivity

• Technical issues: many targets, inhibition control necessary,…• Turn around time of most assays suboptimal

UZ Leuven data: Ct value dependent on platform and gene target

M. Depypere, S. Desmet et al.

UZ Leuven data: Ct value in correlation to days of symptom onset

M. Depypere, S. Desmet et al.

PCR testing• What is the sensitivity of a SARS-CoV-2 PCR?

This depends most likely on:o Sample type: higher yield with lower respiratory tract samples

(sputum, bronchial- or endotracheal aspirate, BAL probably best performance)

o Patient group:• Outpatient/health care worker with first symptoms of disease

(difficult to assess)• Patient admitted to the hospital with pneumonia (PCR, CT-scan, antibody test

needed to assess sensitivity)• Underlying disease?

o …

Triple packaging Provide clinical information on specific request form: TRIAGE

https://epidemio.wiv-isp.be/ID/Pages/2019-nCoV.aspx

https://epidemio.wiv-isp.be/ID/Documents/Covid19/COVID-19_Diagnostic_Labs_NL.pdf

44

55

https://www.finddx.org/covid-19-backuplp/pipeline/

MANY DIFFERENT ASSAYS !

MANY DIFFERENT ASSAYS !

Also for antigen and antibody tests

Detection of highly conserved nucleocapsid protein antigen

COVID-19 Ag Respi-Strip®

P. Mertens et al. Submittted

Multicenter retrospective evaluation of COVID-19 Ag Respi-Strip®

UZ Leuven evaluation of COVID-19 Ag Respi-Strip®

3067

70%

14

83

30%

15

No samples = 97

COVID-19 Epidemiologisch bulletin van 9 april 2020

Preliminary evaluation results are promising

Antibody tests• >100 tests available but clinical validation is lacking• Different formats: rapid lateral flow assays versus ELISA’s• Diagnostic value: can provide microbiological confirmation of COVID-19 in

patients with diagnosis based on CT-scan only• Can give information about proportion of different populations that were

infected, may be helpful for policy makers• Will help in the profiling of the COVID-19 spectrum (subclinical infection,

atypical presentation, ….) and to gain better knowledge about the prognosis• But much more research needs to be done …..

o Can people with antibodies be considered as immune and how long will immunity last? o Do people who had mild or no symptoms gain the same protection? o Will the virus mutate to overcome the body’s immunity?