Testing algorithms used at Bureau of Labs Michigan Department of Community Health

1
Testing algorithms used at Bureau of Labs
Michigan Department of Community Health

• Information on testing algorithms for processing
  and reporting serological assays on arbovirus
  panel with specific reference to West Nile Virus
  testing

2
(No Transcript)
3
Notes to Slide 1

• CSF is the preferred specimen to look for IgM
  antibodies to establish a diagnosis of WNV
  encephalitis.
• If the result is negative, the submitter and the
  local health department will be informed via
  EPIC, the lab reporting system.
• If the result is positive on the first run, this
  is considered a Presumptive Positive and a
  notification is made to the to the local health
  department and the submitter. Please note that
  this is not a confirmed positive and should not
  be characterized that way.
• If there is sufficient CSF, the EIA test is
  repeated, and a repeat positive result is
  reported out on EPIC ( Electronic reporting
  system) to the submitter and the local health
  department as a confirmed positive result. This
  would meet the case definition of a confirmed
  case of West Nile Virus encephalitis for
  surveillance purposes. If the test result is
  equivocal, a request will be made for
  convalescent serum ( drawn at least 22 days post
  onset of illness).This case would be classified
  as a probable case of West Nile Virus
  encephalitis.
• If there is insufficient CSF for a repeat test,
  the result is reported out as QNS (quantity not
  sufficient) and a request is made from the
  submitter for a serum sample.

4
Slide 2
Hold and request Convalescent serum
No
CNS symptoms
Testing Approved by Lab Manager
Neg
Report
IgM ELISA 1st Run
Pos
IgM ELISA 2nd Run
Pos
PRNT on acute serum
Pos
5
Notes to Slide 2

• Acute serum sample when received at MDCH will be
  held and a request will be sent for a
  convalescent sample ( drawn at least 22 days post
  onset of the illness). This is due to the
  documentation of persistence of IgM antibodies in
  serum specimens up to 525 days post onset of
  illness.
• If a convalescent serum is not available, contact
  the Virology Lab Manger. In cases where the
  history and clinical picture are suggestive of a
  recent WNV infection, a Plaque Reduction
  Neutralization test (PRNT) will be performed on
  the acute specimen. If this is confirmed, the
  test result will be considered positive and the
  case will be classified as a Confirmed Case of
  WNV.
• If a convalescent serum is available it will be
  tested along with the acute serum in a PRNT and
  the titres compared. A four-fold increase in
  titre is evidence of a recent infection and the
  test will be reported as positive and the case
  considered a Confirmed Case of WNV.
• 4. The submitter, Epidemiology and the local
  health department will be notified of the results
  via EPIC.

6
Slide 3
Single serum with Documented CNS symptoms or
paired sera without 4 x increase in titer
IgM ELISA () Netralizing Antibody (-)
Test for EEE, SLE and CGV
Single serum collected too early (0-8 d) after
onset of symptoms
Paired sera
No WNV Case
Probable WNV Case
7
Notes for Slide 3

• In a few cases there will be results which are
  more difficult to interpret.
• A single serum sample from a patient who has
  documentation of CNS symptoms, but who has a
  positive EIA and a negative PRNT could have an
  encephalitis due to another flavivirus. The EIA
  could be positive because of the cross-reactivity
  that can occur with flaviviruses. The PRNT is
  considerably more specific and can discriminate
  between the viruses.
• If the tests for EEE and the California group of
  encephalitic viruses (CGV) are positive, the case
  should be reported and investigated as a EEE or
  other viral encephalitis
• If the tests for SLE, EEE and CGV are negative
  then it may be that the serum was collected too
  early for the generation of sufficient IgG
  antibody to be detected in the plaque reduction
  neutralization test. If the serum was collected
  within 8 days of symptom onset the case is
  classified as a Probable case of WNV
• If the serum was collected more than 8 days after
  the onset of symptoms the test result would not
  be considered positive. This would be classified
  
• as Not a Case.