Testing for influenza and variant flu strains

Testing of seasonal and variant strains of influenza, and information on specimen collection and shipping to the Massachusetts State Public Health Laboratory (MA SPHL).

Table of Contents

Rapid testing

Point of care rapid tests capable of detecting influenza A and B virus infections are available, but healthcare providers and public health personnel should be aware that rapid influenza diagnostic tests have limited sensitivity and false negative results are common. Thus, negative results from rapid influenza diagnostic test should not be used to guide treatment decisions. In addition, false positive tests can occur and are more likely when influenza is rare in the community. When laboratory confirmation is desired, the preferred tests are polymerase chain reaction (PCR) and/or viral culture.

MDPH  discontinued the use of the Rapid Influenza Diagnostic Report Form and no longer requires reporting of rapid flu tests.

Polymerase Chain Reaction (PCR) and Viral Culture Testing

Laboratories in Massachusetts report all positive influenza tests they perform to the Massachusetts Department of Public Health (MDPH), including PCR and viral culture tests.

Variant flu

When an influenza virus that normally infects animals (such as pigs or birds) is found in people, it is called a variant influenza virus and is designated with the letter “v” after the subtype.

Most human infections with variant viruses have occurred in people exposed to infected pigs (e.g. children exposed to pigs at a fair or workers in the swine industry), but there have been some instances of person-to-person spread of variant viruses. Worldwide, most

Variant strain testing

If a clinician suspects a variant strain of influenza, a specimen should be submitted promptly to the MA SPHL using the Respiratory Surveillance Specimen Submission Form. (To process this request please call (617) 983-6800.)

Testing at the State Public Health Laboratory

In addition to variant strain testing and as part of a more comprehensive respiratory surveillance initiative, MA SPHL performs testing on submitted samples from volunteer surveillance sites (ILINet) to confirm typing and subtyping of circulating influenza viruses. If negative for influenza and SARS-CoV-2, testing for evidence of adenovirus, respiratory syncytial virus (RSV) A/B, parainfluenza virus (PIV) types 1-4, coronavirus (HCoV) HKU1, OC43, NL63, 229E, human metapneumovirus (HMPV), and rhinovirus/enterovirus (RHV/ENT), using a multiplex PCR respiratory viral panel will occur.

Specimen collection and shipping to MA SPHL

Flu specimens should be collected as soon as possible after onset of illness, preferably within three days (72 hours). Specimens collected after 72 hours are usually unsuitable for testing. Specimens should be submitted immediately after collection to MA SPHL, in order to be tested within three days of collection. If samples will be shipped to MA SPHL >3 days from collection or on a Friday, but are collected within 72 hours, they should be frozen at < -20ºC and shipped with ice packs on the next business day. This variation must be noted on the specimen submission form to avoid an “unsatisfactory for testing” designation.

Find State Public Health Laboratory specimen submission forms in the downloads section of the Influenza information for healthcare and public health professionals handbook.

Contact for Testing for influenza and variant flu strains

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