CDC Releases Updated H3N2v Guidance

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Although its pandemic potential and overall threat to public health are currently considered low, the CDC isn’t taking the re-emergence of swine variant influenza lightly. As with any novel flu virus to which a portion of the population has little or no immunity, the absolute risks cannot be fully quantified.

 

While only rarely detected before 2011, in 2012 more than 300 swine `variant’ infections were confirmed (see A Variant Swine Flu Review) in the United States, mostly linked to attendance of state and county fairs.

 

Based on recently published studies, this was likely a substantial undercount (see CID Journal: Estimates Of Human Infection From H3N2v (Jul 2011-Apr 2012).

 

 

Over the past week, Indiana reported 12 new H3N2v infections (see Indiana Reports 8 More H3N2v Cases), nearly all linked to attendance of the Grant county fair in mid-June.

 

With the county and state fair season just getting underway, yesterday the CDC released two new interim guidance documents on H3N2v for local public health agencies; one on case definitions, and the other on surveillance and specimen collection.

 

 

Interim Guidance on Case Definitions to be Used For Investigations of Influenza A (H3N2)v Virus Cases

Posted on July 3, 2013

This document provides updated interim guidance for state and local health departments conducting investigations of infections with influenza A (H3N2) variant (H3N2v) viruses. Influenza viruses that typically infect swine are referred to as “variant” when they infect humans. The following definitions are for the purpose of investigations of confirmed cases and cases of influenza A (H3N2)v virus infection under investigation. CDC is requesting notification of all confirmed cases of influenza A (H3N2)v virus infection within 24 hours of identification. When possible, state health departments are encouraged to investigate all potential cases of influenza A (H3N2)v virus infection further to determine case status.

Case Definitions for Infection with Influenza A (H3N2)v Virus

Confirmed: Influenza A (H3N2)v virus infection in a patient with laboratory confirmation by:

• Reverse-transcription polymerase chain reaction (RT-PCR) testing or genetic sequencing results positive for influenza A (H3N2)v virus at the CDC Influenza Division Laboratory

OR

• RT-PCR testing results at a public health laboratory consistent with influenza A (H3N2)v virus using a CDC-approved assay (for example, InfA, H3, and pdmInfA positive results, and H1 and pdmH1 negative results using the CDC Flu rRT-PCR Dx Panel)¹. Please see Interim Guidance on Specimen Collection, Processing, and Testing for Patients with Suspect Influenza A (H3N2)v Virus Infection for additional guidance on testing for H3N2v viruses.

Case Under Investigation: Illness compatible with influenza² in a patient meeting at least one of the epidemiologic criteria below for whom laboratory confirmation is not known or pending, or for whom test results do not provide a sufficient level of detail to confirm influenza A (H3N2)v virus (e.g., a positive rapid influenza diagnostic test).

• Recent close contact³ (within 7 days of illness onset) with confirmed cases of influenza A (H3N2)v virus infection

OR

• Recent contact (within 7 days of illness onset) with swine or recent attendance at an event (such as an agricultural fair) where swine were present. Contact with swine may be direct contact (i.e., touching or handling a pig) or indirect contact (coming within about 6 feet (2 meters) of a pig without known direct contact).

¹ This laboratory result is reportable as “presumptive positive” for influenza A (H3N2v) as specified in the CDC Flu rRT-PCR Dx Panel in vitro diagnostic (IVD) package insert. Although State public health laboratories are able to report and act upon this result, all specimens with “presumptive positive” results should be sent to CDC for additional testing. Please see Data Interpretation Update to the CDC Flu rRT-PCR Dx Panel  [27 KB, 1 page] for additional guidance on interpretation of the CDC Flu rRT-PCR Dx Panel.

² Illness compatible with influenza may present as influenza-like illness (ILI) [fever ≥100°F plus cough or sore throat]. Note that influenza may not cause fever in all patients (especially in patients under 5 years of age, over 65 years of age, or patients with immune-suppression), and the absence of fever should not supersede clinical judgment when evaluating a patient for illness compatible with influenza.

³ Close contact may be regarded as coming within about 6 feet (2 meters) of a confirmed case while the case was ill (beginning 1 day prior to symptom onset and continuing until resolution of illness). This includes healthcare personnel providing care for a confirmed case, family members of a confirmed case, persons who lived with or stayed overnight with a confirmed case, and others who have had similar close physical contact.

 

 

 

Interim Guidance for Enhanced Influenza Surveillance: Additional Specimen Collection for Detection of Influenza A (H3N2) Variant Virus Infections

Posted on July 3, 2013

Summary

This document is an update to interim enhanced surveillance guidance posted in 2012. In anticipation of the 2013 agricultural fair season, states should consider expanding surveillance to include reverse-transcription polymerase chain reaction (RT-PCR) testing of specimens from ILINet providers statewide, of specimens collected from people with ILI reporting recent swine contact or agricultural fair attendance, and of specimens collected from people with unusual or severe presentations of ILI. States should also consider collection of specimens from outbreaks of ILI among children in child-care and school settings, since these settings have been associated with person-to-person H3N2v virus transmission in 2011. CDC will continue to evaluate new information as it becomes available and will update this guidance as needed.

Background

From July-September 2012, 306 infections with an influenza A (H3N2) variant (H3N2v) were identified in 10 states. Influenza viruses that typically infect swine are referred to as “variant” when they infect humans. During the 2012 outbreak, most cases reported agricultural fair attendance and contact with swine prior to illness. Few instances of person-to-person transmission were identified, and there was no evidence of sustained community-wide transmission. Confirmed H3N2v cases were identified primarily among children (<18 years of age), and limited serologic studies indicate that children, primarily those younger than 9 years, have increased susceptibility to H3N2v. However, some adult H3N2v cases were identified.

 

This document provides interim guidance to state and local health departments for enhanced surveillance and testing by (RT-PCR) for influenza viruses. Use of RT-PCR testing is important in order to identify which influenza A virus subtypes (e.g. H3N2v viruses versus seasonal H1N1 or H3N2 viruses) are circulating. These guidelines have been developed in an effort to facilitate timely detection and investigation of H3N2v cases by targeting patients with influenza-like illness (ILI) for influenza testing by RT-PCR.

 

CDC would like state and local health departments to consider the following recommendations for influenza surveillance and testing.

1. All state public health laboratories should use the CDC Human Influenza Real-Time rRT-PCR FLU Diagnostic Panel to screen specimens for InfA, InfB, and RP.
2. Test all InfA-positive specimens with the CDC Influenza A Subtyping kit using all primer/probe sets: H1, H3, pdmInfA and pdmH1. Detailed guidance for testing can be found in the influenza surveillance diagnostic testing algorithm disseminated recently by Association of Public Health Laboratories  [27 KB, 1 page]. Specimens that are positive for H3N2v virus should be sent to CDC Influenza Division for additional testing as soon as possible.
3. Conduct contact tracing of confirmed influenza A (H3N2)v cases to gather more information about the epidemiology of the virus and modes of transmission. Contact tracing is essential to evaluate potential person-to-person transmission.
4. Currently, while seasonal influenza viruses are circulating at low levels, CDC recommends collection of specimens from patients with ILI, and sending these specimens to the state or local laboratory for rRT-PCR testing. States should specifically consider collection of specimens across the state from patients presenting with ILI in the following high priority areas:
   1. All ILINet providers statewide.
   2. Medically attended ILI and acute respiratory infection (ARI), especially in patients who have had recent contact (< 7 days prior to illness onset) with swine or recent attendance at an agricultural event where swine are present.
   3. ILI outbreaks statewide, particularly among children in child care and school settings, since these settings were associated with person-to-person transmission of H3N2v in the past.
   4. Unusual or severe presentations of ILI statewide, including hospitalized persons.
   5. Medically attended ILI and acute respiratory infection (ARI), especially in children in areas where confirmed H3N2v cases have occurred.

CDC will continue to evaluate new information as it becomes available and will update this guidance as needed.