H3N2v Update: New Cases Reported, Limited Person-to-Person Transmission Detected [edited]

August 29, 2012 — 

As of the latest official report from the Centers for Disease Control and Prevention (CDC) dated August 24, 2012, 52 additional cases of H3N2v are being reported, bringing the total number of such infections since July 2012 in the United States to 276 across 10 states. Investigations into H3N2v cases indicate that the main risk factor for infection is exposure to pigs, mostly in fair settings; however, CDC also is reporting three instances of likely human-to-human spread of this virus during the current outbreaks. Found in pigs in 2010 and first detected in humans in July 2011, this H3N2 variant virus appears to be more transmissible from pigs to people than other variant viruses. The CDC is working with states to respond to this evolving situation and continues to monitor the situation closely.

According to CDC’s Dr. Joseph Bresee “limited human-to-human spread of this virus has been seen in the past, but the H3N2v virus has not previously -- and is not now -- spreading easily from person-to-person.” According to Bresee, “Most cases are occurring in children who are exhibiting pigs, or helping to exhibit pigs and have occurred after a lot of very close contact with pigs over a relatively long period of time.” Dr. Bresee is Chief of the Epidemiology and Prevention Branch in CDC’s Influenza Division.

The 52 new cases reported this week are from the states of Illinois (1), Maryland (12), Michigan (4), Minnesota (1), Ohio (26), Pennsylvania (2), and Wisconsin (6). These are the first reports of H3N2v with the pandemic M gene from Maryland and Minnesota. The 6 cases in Maryland are reported to have had exposure to pigs prior to their illness. The one case in Minnesota was confirmed following a visit to a live animal market where pigs were present. Cumulative totals for 2011 and 2012 by state are available in the H3N2v case count table. The remaining cases being reported this week are associated with exposure to pigs at fairs.

The three instances of likely person-to-person spread of H3N2v were recently identified during investigations of cases and their household contacts and are not epidemiologically linked to one another. In all three cases, transmission is thought to have occurred from one person to another person without further spread to additional people. Each of these three instances of likely person-to-person spread happened between 2 people living in the same household, with the initial infection in each household being associated with pig exposure at an agricultural fair.

CDC is monitoring for changes in the virus and potential person-to-person transmission of H3N2v. So far, genetic analysis of the viruses submitted to CDC show that all viruses are nearly identical, and very similar to the H3N2v viruses found in 2011.

Additional information is available on the CDC website. The National Pork Board has also compiled a number of resources which are also available on the Pork.org website.

Source: CDC Report, August 24, 2012