Tuesday, August 16, 2016

CDC: Interim Guidance for Clinicians on Human Infections with Variant Influenza Viruses


With 4 recently diagnosed H3N2v cases (2 in Michigan, 2 in Ohio), and more reports of sick pigs at state and county fairs in Michigan, local and federal health authorities are warning fairgoers and doctors to be on the lookout for additional cases of swine variant influenza infection.

The last big swine variant outbreak occurred in 2012, when more than 300 people across ten (mostly) Midwestern states were infected, nearly all linked to county and state fair exposures.

While humans have a long history of exposure to seasonal H3N2 flu viruses, research has shown only limited community immunity to these variant strains (see CIDRAP: Children & Middle-Aged Most Susceptible To H3N2v).

The good news is that while several hundred infections were recorded in 2012, sustained and efficient community transmission was not observed, and for the most part, the virus only caused mild to moderate illness.

It is important to note that only can swine pass flu viruses on to people, people can pass flu viruses on to swine.  Something we saw happen around the world after the 2009 H1N1 pandemic virus emerged and began transmitting in humans. 

This bi-directional transfer of influenza viruses allows for even greater mixing and matching of genes, and explains how the H3N2v virus picked up the M (matrix) gene from the 2009 H1N1pdm virus in 2012.

Yesterday the CDC released a new set of interim guidance for clinicians on identifying, reporting, and managing swine variant influenza infections.  This includes not only H3N2v, but H1N1v and H1N2v as well.

Due to its length I've only posted excerpts.   Clinicians and other interested persons should follow the link to read the guidance in its entirety.

Interim Guidance for Clinicians on Human Infections with Variant Influenza Viruses

August 15, 2016


Influenza A viruses circulating in swine that have infected humans are referred to as “variant” viruses and denoted with a letter “v”. Human infections with H1N1v, H3N2v and H1N2v viruses have been detected in the United States.

Most commonly, human infections with variant viruses occur in people with exposure to infected swine (e.g., children near swine at a fair or workers in the swine industry). There have been documented cases of multiple people becoming sick after exposure to one or more infected swine and also rare cases of limited spread of variant influenza viruses from person-to-person. The vast majority of human infections with variant influenza viruses do not result in person-to-person spread. However, each human infection with a swine influenza virus should be fully investigated to be sure that such viruses are not spreading in an efficient and ongoing way in humans and, if infected animals are identified, to limit further exposure of humans to these animals.

Clinical Presentation and Risk Groups

Clinical characteristics of human infections with variant viruses generally have been similar to signs and symptoms of uncomplicated seasonal influenza, including fever, cough, pharyngitis, rhinorrhea, myalgia, and headache. Vomiting and diarrhea also have been reported in some infections in children. Milder clinical illness is possible, including lack of fever. The duration of illness appears to be similar to uncomplicated seasonal influenza, approximately 3 to 5 days. While assumed to be similar to seasonal influenza virus infection, the duration of viral replication and possible infectiousness of variant virus infection has not been studied.

Exacerbation of underlying conditions (e.g., asthma) has occurred. The same people at increased risk for complications of seasonal influenza are likely at high risk for serious complications from variant virus infection, including children younger than 5 years, pregnant women, people 65 years and older, those who are immunosuppressed, and persons with chronic pulmonary, cardiac, metabolic, hematologic, renal, hepatic, neurological or neurodevelopmental conditions, as well as those with other co-morbidities, including extreme obesity.

Clinical Diagnosis

Variant virus infection cannot be distinguished by clinical features from seasonal influenza virus infection, or from infection with other respiratory viruses that can cause influenza-like illness (fever and either cough or sore throat). Therefore, the key to suspecting variant virus infection in an ill patient is to elicit an epidemiological link to recent swine exposure in the week prior to illness onset. Exposure can be defined as follows:

  • Direct contact with swine (e.g., showing swine, raising swine, feeding swine, or cleaning swine waste)
  • Indirect exposure to swine (e.g., visiting a swine farm or walking through a swine barn), especially if swine were known to be ill; or
  • Close contact (within 2 meters or approximately 6 feet) with an ill person who had recent swine exposure or is known to be infected with a variant virus.

For any ill person with an exposure as defined above, respiratory samples should be taken for testing. Clinicians should obtain a nasopharyngeal swab or aspirate (or a combined nasal swab and throat swab), place the swab or aspirate (or combined specimen) into viral transport medium, and contact their state or local health department to arrange transport and request a timely diagnosis at a state public health laboratory. Only CDC and state public health laboratories can confirm variant virus infections. If testing is also going to be done at the hospital or clinic, the specimen should be split or two specimens should be taken so that one can be immediately sent to the health department for testing.

  • Laboratory Diagnosis and Test Interpretation – Hospital and Clinical Laboratories
  • Clinician Reporting
  • Clinical Management
  • Vaccination
  • Prevention
       (Continue . . . )

While four variant infections over two weeks does not a crisis make, it is enough of a warning shot that public health agencies must take note and respond.

Swine influenza viruses - like all viruses - are constantly evolving, and certainly have the potential to become better adapted to human hosts over time.

While no one can forecast when the next pandemic will emerge, or even from where, swine variant viruses are definitely viewed as contenders.  Some recent blogs on the threat they pose include:

PNAS: The Pandemic Potential Of Eurasian Avian-like H1N1 (EAH1N1) Swine Influenza
Eurosurveillance: Seroprevalence Of Cross-Reactive Antibodies To Swine H3N2v – Germany
JID: Evolutionary Dynamics Of Influenza A Viruses In US Exhibition Swine 
Live Markets & Novel Flu Risks In The United States