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 decisions regarding treating patients with influenza antiviral medications. 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 has discontinued the use of the Rapid Influenza Diagnostic Report Form and faxed reporting of the rapid flu test results by providers is no longer necessary.

Polymerase Chain Reaction (PCR) and Viral Culture Testing

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

Testing at the State Public Health Laboratory: As part of a more comprehensive respiratory surveillance initiative, MA SPHL performs testing to confirm typing and subtyping of circulating influenza viruses, followed by testing of influenza and SARS-CoV-2 negative samples for the 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. 

Variant strain testing

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

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. Rarely, a variant virus evolves sufficie

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 Monday. 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.



Infectious Disease Division (617) 983-6550
Urgent calls and infectious disease reporting (617) 983–6800
Laboratory Sciences Division (617) 983–6201


State Public Health Laboratory
305 South Street
Jamaica Plain, MA 02130

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