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Delaware Health Alert Network #272

August 8, 2012 8:25 am


Health Advisory
INCREASE IN INFLUENZA A H3N2v VIRUS INFECTIONS IN U.S.

Delaware is not among three states reporting cases of Influenza A H3N2v virus and has had not reported any case of seasonal influenza since June 12th, 2012. Typically, the flu season occurs in the fall and winter but the peak of flu season has occurred anywhere from late November through March.

Nationally, multiple infections with variant* influenza A (H3N2v) viruses have been identified in 3 states in recent weeks. From July 12 through August 3, 2012, 16 cases of H3N2v were reported and confirmed by Centers for Disease Control (CDC). This virus was first detected in humans in July 2011. It has also been isolated in U.S. swine in many U.S. states. Since July 12, 2011, there have been 29 cases of H3N2v virus infection. The H3N2v viruses have been reported in the following states: Hawaii (1), Indiana (7), Iowa (3), Ohio (10), Maine (2), Pennsylvania (3), Utah (1), and West Virginia (2).

All 29 cases were infected with H3N2v viruses that contain the matrix (M) gene from the influenza A (H1N1)pdm09 virus. This M gene may make transmission easier to and among humans, compared to other variant influenza viruses. All cases have been laboratory-confirmed at CDC. Each of the 16 cases identified since July 12, 2012, reported contact with swine prior to illness onset; in 15 cases, contact occurred while attending or exhibiting swine at an agricultural fair. While the viruses identified in these cases are genetically nearly identical, separate swine exposure events in each state were associated with human infections. There is no indication that the cases in different states are related epidemiologically.

Clinical characteristics of the 16 H3N2v recent cases have been generally consistent with signs and symptoms of seasonal influenza, and have included fever, cough, pharyngitis, myalgia, and headache. No hospitalizations or deaths have occurred among the 16 confirmed cases since July 2012. Public health and agriculture officials are investigating the extent of disease among humans and swine, and additional cases are likely to be identified as the investigation continues.

Interim Recommendations for Health Care Providers

  • Clinicians who suspect influenza in persons with recent exposure to swine should obtain a nasopharyngeal swab or aspirate from the patient, place the swab or aspirate in viral transport medium, and contact the Public Health Laboratory at 302-223-1520 to arrange transport and request a timely diagnosis.
  • Reverse-transcription polymerase chain reaction (RT-PCR) testing for influenza should be considered for patients with influenza-like illness prior to the start of the traditional influenza season in October.
  • RT-PCR testing for influenza should be considered throughout the year for patients with influenza-like illness reporting recent swine exposure and for those who can be epidemiologically linked to confirmed cases of variant influenza.
  • Commercially available rapid influenza diagnostic tests (RIDTs) may not detect H3N2v virus in respiratory specimens. Therefore, a negative rapid influenza diagnostic test result does not exclude infection with H3N2v or any influenza virus. In addition, a positive test result for influenza A cannot confirm H3N2v virus infection because these tests cannot distinguish between influenza A virus subtypes (they do not differentiate between human influenza A viruses and H3N2v virus). Therefore, respiratory specimens should be collected and sent for RT-PCR testing to the Public Health Laboratory.
  • Clinicians should consider antiviral treatment with oral oseltamivir or inhaled zanamivir in patients with suspected or confirmed H3N2v virus infection. Antiviral treatment is most effective when started as soon as possible after influenza illness onset.

Testing

DPH strongly encourages providers (for example, school wellness centers, long term care facilities, physicians, etc.) to submit influenza specimens to the DPH Laboratory for culture molecular (PCR) confirmation and subtyping (throat/NP/nasal wash) to assist with the detection of influenza. To submit a specimen for culture influenza testing, contact the Public Health Laboratory (302-223-1520) to request influenza virus isolation kits and obtain information about specimen transport to the laboratory. Culture Molecular detection and subtype testing by the Public Health Laboratory is done free of charge and results are sent back to the requesting physician or hospital as soon as test results are available.

Novel influenza A virus infection has been a nationally notifiable condition in the United States since 2007. Since that time, human infection with animal-origin influenza viruses has been rare, with ≤6 cases reported each year, until 2011 when 14 cases were identified. While most of the cases are thought to have been infected as a result of close contact with swine, limited human-to-human transmission of this virus was identified in some cases in 2011. Therefore, enhanced influenza surveillance is indicated, especially in regions and states with confirmed H3N2v cases.

For more information


*Variant:Influenza viruses that circulate in swine are called swine influenza viruses when isolated from swine, but are called variant viruses when isolated from humans

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