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Diagnosis of Severe Acute Respiratory Syndrome SARS

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Diagnosis of Severe Acute Respiratory Syndrome (SARS) Clinical ... Questions histopathology and rate of positivity. SARS Etiologic Agent. Order: Nidovirales ... – PowerPoint PPT presentation

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Title: Diagnosis of Severe Acute Respiratory Syndrome SARS


1
Diagnosis of Severe Acute Respiratory Syndrome
(SARS)
  • Clinical characteristics of illness
  • Epidemiologic link to SARS, i.e. ,travel or
    contact
  • Laboratory evidence of SARS-CoV infection
  • Type of specimen
  • Timing of specimen collection
  • Laboratory assay to detect infection

2
Association Between SARS-CoV and SARS Disease
  • Infection in SARS patients virus and serology
  • CDC
  • Germany, Canada, Hong Kong, Taiwan, Singapore,
    France, China, Thailand, etc.
  • Neg-serology in non-SARS patients (1000 sera at
    CDC, 280 HK)
  • Virus in lung tissue/BAL specimen
  • Identical sequences different outbreaks (c/w
    point source)
  • US Hong Kong, Thailand, Singapore, Taiwan,
    Vietnam, Canada, Germany
  • Pulmonary pathology in monkey model
  • Questions histopathology and rate of positivity

3
SARS Etiologic Agent
  • Order Nidovirales
  • Family Coronaviridae
  • Torovirus
  • Coronavirus
  • Grp I
  • Grp II
  • Grp III

4
Coronaviruses, Hosts and Diseases
  • Antigenic
  • Group Virus Host Respiratory Enteric
    Other
  • I HCoV-229E human X
  • TGEV pig X
  • PRCoV pig X
  • FIPV cat X X
    X
  • FECoV cat X
  • CCoV dog X
  • II HCoV-OC43 human X ??
  • MHV mouse X X
    X
  • RCoV rat X X
  • HEV pig X X
  • BCoV cattle X X
  • III IBV chicken X X
  • TCoV turkey X

5
SARS-CoV Genome Organizationand mRNA Synthesis
A
E
ORF 1a
N
M
S
ORF 1b
5,000
10,000
15,000
20,000
25,000
30,000
1
C
B
2
1
3
20,001
30,000
25,000
kB
X1
X3
E
9.0
N
M
6.0
5.0
4.0
S
X2
X4
X5
3.0
2.5
2.0
1.5
8.3 kb
RNA 2
4.5 kb
1.0
RNA 3
RNA 4
3.4 kb
0.5
2.5 kb
RNA 5
RNA 6
1.7 kb
6
Laboratory Diagnosis of SARS Infection
  • Type and timing of specimen collection (we need
    to know more)
  • Type of assays
  • Sensitivity
  • Specificity
  • Interpretation of results

7
Laboratory Assays for SARS
  • Detection of virus
  • EM in clinical specimens (CoV-like particles)
  • Isolation of virus
  • Detection of viral antigens (IHC for tissue,
    ?sensitivity of IFA or ELISA for respiratory
    specimens)
  • Detection of viral RNA (PCR)
  • Respiratory secretions
  • Stool specimens
  • Urine specimens
  • Tissue lung and kidney
  • Detection of SARS-specific antibody
  • IFA
  • ELISA
  • Neutralization

8
Real-Time RT-PCR (TaqMan)
9
Characteristics of SARS-CoV PCR
  • Limited experience/data
  • Specimens
  • Upper respiratory maybe 50 positivity in
    acute-phase specimens
  • Stool possibly higher sensitivity later in
    illness, e.g., 10-14 days
  • Sputum/BAL probably higher rate of positivity
  • Other specimens, urine, blood, tissues, ?
  • Interpretation of Results
  • Negative -- does not rule out SARS-CoV infection
  • Positive possibility of false positive (test
    error/contamination)

10
SARS CoV Antibody Assays
11
Characteristics of SARS-CoV Antibody Assays
  • Limited data
  • Very low or absent antibody in controls and
    persons without acute SARS
  • Acute sera may be positive as early as 6 days
    after onset of sera
  • Convalescent sera should be positive by 21 days
    after onset
  • Interpretation of results
  • Single positive sera indicative of acute
    infection
  • Later diagnostic rise in antibody between acute-
    and convalescent-phase sera or IgM antibodies may
    be need to diagnose acute infection
  • Convalescent-phase serum specimen collected gt21
    days after onset of illness is required to
    confirm lack of antibody response to infection
  • False positive/false negative results

12
Other Tests for SARS Infection
  • Limited data
  • Tissue culture isolation
  • Electron microscopy for CoV-like particles
  • Immunohistologic or in situ studies of tissue
    specimens
  • IFA or ELISA assays SARS-CoV antigens in
    respiratory or other specimens (? Likely to be
    sufficiently sensitive)

13
Conclusions
  • SARS is a clinical and epidemiologic diagnosis
  • Laboratory testing can diagnose SARS-CoV
    infection during the acute illness
  • Laboratory testing can not rule out infection
    until the convalescent phase of illness
  • Dual infections, e.g., SARS-CoV and human
    metapneumovirus, can occur in patients with SARS
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