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#12,770
On Thursday, in Maryland DOH: 7 Fairgoers Test Positive For Swine Variant H3N2v, we learned of an outbreak of swine variant influenza among attendees of the Charles County Fair, and the decision to close the swine venues at two upcoming county fairs (Calvert County & St. Mary's).
The CDC describes Swine Variant viruses in their Key Facts FAQ.
What is a variant influenza virus?
When an influenza virus that normally circulates in swine (but not people) is detected in a person, it is called a “variant influenza virus.” For example, if a swine origin influenza A H3N2 virus is detected in a person, that virus will be called an “H3N2 variant” virus or “H3N2v” virus.Over the past dozen years we've seen just over 420 swine variant cases (H1N1v, H1N2v, H3N2v) reported by the CDC with 307 coming in just one year (2012). Last year we saw an uptick in cases (see MMWR: Investigation Into H3N2v Outbreak In Ohio & Michigan - Summer 2016), as we have again this summer.
The 7 cases reported on Thursday have not yet been added to the CDC's total, and a brief notice posted on the Maryland Health Department website now indicates the number of presumptive cases has risen to 10.
Influenza A (H3N2) Variant Virus
Background
The Maryland Department of Health has presumptively identified the influenza virus strain H3N2v (variant flu) in Maryland residents who had close contact with pigs at the Charles County Fair. None of the infected individuals has developed serious illness or been hospitalized.
Influenza is an infection caused by the influenza virus which can affect people and other animals, including pigs and birds. Symptoms for the H3N2v strain are the same as seasonal flu and include fever and respiratory symptoms, such as sore throat and cough. Historically, there is limited human to human transmission from this strain of variant flu. The treatment recommendations for this strain of influenza are the same as for seasonal flu.
It is recommended that people with influenza-like illness contact their healthcare provider and inform them if they have had pig contact within the past seven days. Providers are advised to contact their local health departments if they suspect variant flu in their patients to coordinate appropriate testing with their local health department. For local health department contact information, visit: https://health.maryland.gov/Pages/departments.aspx
Maryland Cases (as of September 22, 2017)
In an attempt to better quantify the size of this outbreak, the Maryland Department of Health has issued a letter to clinicians with guidance for testing and reporting. An excerpt from the letter describes when testing is appropriate:10 presumptive positive cases
When to suspect variant influenza virus
Variant influenza 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 7 days prior to illness onset,specifically:
- Direct contact with swine (e.g., showing swine, raising swine, feeding swine, or cleaning swine waste); or
We've seen studies in the past suggesting that only a fraction of cases are ever identified (see CID Journal: Estimates Of Human Infection From H3N2v (Jul 2011-Apr 2012), and while H3N2v is viewed as having only low to moderate pandemic potential, the CDC is always keen to investigate whenever a zoonotic virus like swine H3N2 jumps species.A weaker epidemiological link would be:
- 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.
- Indirect exposure to swine (e.g., visiting a swine farm or walking through a swine barn), especially if swine were known to be ill
While both local and state health departments are reporting no serious illnesses or hospitilzations, several local media outlets are reporting on an 8-year-old girl hospitalized with swine flu after attending Charles County Fair, mother says.Normally mild or moderate infections, serious illness and even deaths have occasionally been reported with swine variant viruses (see here, here, and here). Despite 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).
Although it may or may not be related to swine variant influenza (tests are pending), late yesterday another fair in Maryland closed their pig barn due to the discovery of a sick pig, and reports of a child hospitalized with flu-like symptoms with prior exposure.
This report from the CBS-TV affiliate (WJZ) in Baltimore.
Sick Pig and Child Causes Shut Down Of Frederick Co. Fair Pig Exhibit
September 23, 2017 11:15 PM
BALTIMORE (WJZ) — The swine barn at The Great Frederick Fair was shut down Saturday after state inspectors found at least one pig with a 106-degree fever.
The Frederick News-Post reports that state veterinarian Michael Radebaugh said that a pig at the fair was showing signs of illness, with swine flu as a possible cause.
The Animal Health section of the Maryland Department of Agriculture closed the barn within an hour of symptoms.
(SNIP)
A sick child at Frederick Memorial Hospital was also reportedly showing flu-like symptoms and the fair board was alerted.
The child’s parents told doctors that they had been at the fair and around pigs.
(Continue . . . )We should know more about this incident, and whether it is related to a swine variant virus, in the next few days. While the evidence is still circumstantial, Maryland officials are obviously operating with an abundance of caution.
With state and county fair season continuing into the fall, it would not be unexpected to see additional, scattered reports of swine variant infection from around the nation.H2N2v is the most common swine variant virus reported in the United States, but is far from the only swine flu virus of concern. Co-circulating in North America are also H1N1 and H1N2 swine viruses, along with occasional reassortants like H3N1 (see J. Virol: Novel Reassortant Human-like H3N2 & H3N1 Influenza A Viruses In Pigs).
Globally the picture becomes even more complicated, with reports of other swine flu variants coming from Europe, South America, and Asia. As surveillance and testing is spotty at best, the constellation of of swine flu viruses in circulation is likely much larger and more complex than we know.A few recent blogs on other swine flu threats include:
Virology: Detection & Characterization Of Avian H4N6 In Midwestern Swine (2015)
J. Virology: A Single Amino Acid Change Alters Transmissability Of EAH1N1 In Guinea Pigs
I&ORV: Triple-Reassortant Novel H3 Virus of Human/Swine Origin Established In Danish Pigs
Emerg. Microbes & Inf.: Pathogenicity & Transmission Of A Swine Influenza A(H6N6) Virus - China
Sci Rpts:Reassorted H9N2:pH1N1 Virus Transmission After Serial Passage In Swine
