Archive Issue

2010, Volume 21, Number 3

VirusFAST FACTS: A New Warde Report Feature

By D. L. Wiedbrauk, Ph.D.

We often receive telephone calls from physicians, residents, clerical and nursing personnel, and hospital administrators requesting information about appropriate test selections, test interpretations, and related information. FAST FACTS entries are created in response to these often harried requests for “no frills” information about laboratory tests and how they relate to the clinical picture. FAST FACTS are intended to supplement our on-line catalog which, in itself, provides succinct information about specimen collection and patient preparation. Because this information is concise enough to be conveyed over the telephone, FAST FACTS may allow our client laboratories to quickly respond to these basic information requests.

This month, FAST FACTS entries cover Norovirus, Herpes Simplex Virus Serologies and Influenza Virus Testing — three areas where we receive many requests for information. We hope you find this new feature helpful. To maintain its utility however, WE NEED YOUR HELP! Please contact Client Services (734-214-0300, 734-214-0399 fax, or 800-760-9969) if you would like us to create FAST FACTS entries on other topics.

WML_FastFacts_Norovirus-Testing.pdf

Fast Facts — Norovirus Testing

Recommended Screen – Norovirus Group 1 and 2 PCR (NOROPCR)

Detects and differentiates genogroup 1 and 2 noroviruses. Genogroup IV is not detected, but these infections are very rare. Extremely high virus concentrations are present in stool and vomit from symptomatic patients. Vomit will not be tested (we have not validated that source). Some stool specimens contain substances that interfere with PCR amplification. These specimens will be reported as INHIBITORY. Submitting another specimen is recommended.
Noroviruses are detectable when the patient is symptomatic and for 1–2 weeks thereafter. Stool is the only acceptable specimen. Norovirus PCR is also part of the screening panel used in the Comprehensive Virus Detection (CVD) test. (see below)

Comprehensive Virus Detection (CVD)

Stool specimens are screened by PCR for adenovirus and norovirus. Enterovirus PCR is performed in the Summer and Fall. Provides the fastest turnaround time when the viral etiology is uncertain. PCR turnaround time averages 24 hours from receipt in the laboratory. Recommended when multiple viruses could be causing the clinical presentation.
Specimens that are PCR negative are placed into culture to isolate viral agents that are not covered by PCR testing. Culture methods will not detect norovirus.

Will detect co-infections.


More expensive than an individual PCR test.

Negative stool cultures take 10 days.

Norovirus Antigen EIA Testing

Not recommended for routine use.

Sensitivity is low <50% versus PCR May not detect all noroviruses.

Virus Culture (VC)

Not recommended because noroviruses will not grow in culture.

Norovirus Serologies

Serological testing is a waste of time except for specialized research surveillance studies.

 


WML_FastFacts_Herpes-Simplex-Serologies.pdf

Fast Facts — Herpes Simplex Serologies

HSV IgM

Appears 3–10 days after infection.

During reactivations, 5–30% of patients will produce a low-level IgM response.

Many individuals have a low-level IgM response that cannot be correlated with HSV disease.
Persists for 6–8 weeks. IgM is not useful for separating primary from recurrent HSV infections in patients with HSV IgG. Type-specific IgM testing is useless because HSV IgM cross-reacts
with HSV-1 and HSV-2.

Neonatal IgM Testing

HSV IgM can be helpful in diagnosing neonatal infections. IgM is usually present 3–4 weeks after birth and persists for up to 1 year.

Type Specific HSV IgG antibodies

Type-specific HSV IgG may not be detectable for 12–16 weeks after exposure.

In contrast with traditional (non-type specific) HSV IgG tests where antibody reactivity persists for the patient’s lifetime, some patients appear to lose type-specific HSV IgG antibodies over time. (Antibody reactivity to the peptide antigens can wane.) Some patients do not produce antibodies to the peptides used in the type-specific HSV IgG tests and testing with the older cross-reactive methodologies may be required.



WML_FastFacts_Influenza-Testing.pdf

Fast Facts — Influenza Testing

Recommended Screen — Influenza Virus A and B PCR (FLUPCR)

Detects influenza B, seasonal H1 and H3 influenza A viruses, and the 2009 H1N1 (swine) influenza.

This test will detect and differentiate influenza A from influenza B but it cannot distinguish the individual influenza A virus genotypes. If influenza A genotyping is required, order the FLUGENO test (below).

Influenza virus is usually detectable when symptoms are present and for 5 days thereafter.

Specimen of choice is an NP and throat swab where both swabs are placed into the same viral transport medium. Alternate specimen is a single throat swab. However, this specimen type will have decreased the sensitivity if parainfluenza viruses and RSV are in the rule out list. Other approved specimen types can be found on this website.

Influenza A Genotyping (FLUGENO)

Used to differentiate 2009 H1N1, seasonal H3, and seasonal H1 influenza viruses for influenza A positive samples. Can be useful when contemplating antiviral therapy or when current antiviral therapy is not working. Should not be used as a general screening test.

Virus Culture (VC)

Not recommended for routine testing due to long turnaround times (3–5 day average).

A negative result will be reported in 10–14 days. Deep respiratory cultures are held for 14 days.

Comprehensive Virus Detection (CVD)

Consists of PCR screens for the major viruses that circulate at that time of the year and culture when the PCR tests are negative. Testing algorithm is available upon request. Will detect co-infections.

More expensive than an individual PCR test.
Provides the fastest turnaround time when the viral etiology is uncertain.
Recommended when multiple viruses could be causing the clinical presentation. PCR turnaround time averages 24 hours from receipt in the laboratory. Negative culture takes 10–14 days. Deep respiratory cultures are held for 14 days.

Influenza Serologies

Serological testing is generally a waste of time except for research or special surveillance purposes.