Photo Credit CDC
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Nearly all of the recent cases of H3N2v infection in the Midwest have thus far been associated with exposure to pigs at state and county fairs. Admittedly, testing for the virus has been concentrated mostly among those with known recent swine contacts, and that may entail some bias.
It’s a logical place to start looking, given the swine-origin of the virus. But it’s a surveillance strategy that has the potential to miss other cases in the community.
Yesterday, in an attempt to cast a wider surveillance net, the CDC updated their guidance recommendations to state and local health departments on testing for the H3N2v virus.
Interim Guidance for Enhanced Influenza Surveillance: Additional Specimen Collection for Detection of Influenza A (H3N2) Variant Virus Infections
Posted August 20, 2012
Summary
This document is an update to interim enhanced surveillance guidance first posted in December 2011. In light of the increasing numbers of cases of H3N2 variant virus (H3N2v) and increasing numbers of states reporting H3N2v cases, states should consider expanding surveillance to include rRT-PCR testing of specimens from ILINet providers statewide, 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.
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CDC would like state and local health departments to consider the following recommendations for influenza surveillance and testing.
- 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.
- 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 presumptive positive for H3N2v virus should be sent to CDC Influenza Division for additional testing as soon as possible.
- Conduct contact tracing of confirmed and probable 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.
- Currently, while seasonal influenza viruses are circulating at low levels, CDC recommends increasing collection of specimens from patients with influenza-like-illness (ILI), and having these specimens sent to the state or local laboratory for rRT-PCR testing. States should specifically consider increasing collection of specimens across the state from patients presenting with ILI in the following high priority areas:
- All ILINet providers statewide.
- ILI outbreaks statewide, particularly among children in child care and school settings, since these settings were associated with person-to-person influenza A (H3N2)v virus transmission in 2011.
- Unusual or severe presentations of ILI statewide, including hospitalized persons.
- Medically attended ILI and acute respiratory infection (ARI), especially in children in counties or states where confirmed H3N2v cases have occurred.
With schools across the Midwest beginning their fall session this month, and scores of county and state fairs scheduled over the next couple of months, the need to pin down how this virus behaves – and whether any human-to-human transmission is occurring – increases.
Meanwhile, the debate over whether pigs should be excluded from public venues continues, as illustrated by this story that appeared last night on CIDRAP News, written by Lisa Schnirring.
H3N2v infections spark debate about barring pigs from fairs
Lisa Schnirring
Staff Writer
Aug 21, 2012 (CIDRAP News) – The type of flu transmission occurring mainly in young people directly exposed to pigs at fairs this summer is unprecedented, and health officials should consider keeping pigs away from the events, according to one infectious disease expert who has gone on record with his concerns.
As Minnesota announced its first confirmed and suspected variant H3N2 (H3N2v) infections yesterday, just a few days before the start of its state fair, local and national media outlets such as the Canadian Press aired concerns from Michael Osterholm, PhD, MPH, director of the University of Minnesota's Center for Infectious Disease Research and Policy (CIDRAP), publisher of CIDRAP News, who said that fair organizers should bar swine from fairs this year.
