Michigan HHS Reports 1 Novel (H3N2v) Flu Infection

Credit Wikipedia

#18,235

Yesterday in their weekly FluView Report the CDC reported a novel (H3N2v) flu infection from Colorado, in an individual who had recently attended an agricultural exhibit. This was the 4th swine variant case reported by the CDC in 2024, although due to limited testing and surveillance, this is expected to be an undercount. 

Although it wasn't included in the CDC report, Michigan also reported a novel flu case (h/t Lisa Schnirring @ CIDRAP News) in July.  While the investigation is still ongoing, this patient had no known contact with swine. 

Most swine variant infections are linked - either directly or indirectly - to exposure to pigs, although occasionally we see one where no such connection can be made.  

While their health department believes this is likely an isolated incident, they are advising people with flu-like symptoms to get tested for both COVID and Influenza.

First the statement from the MDHHS, after which I'll have a postscript.

MDHHS confirms detection of influenza A H3N2 variant (swine flu) in Ingham County

August 09, 2024

The Michigan Department of Health and Human Services (MDHHS) and Ingham County Health Department have identified a human case of influenza A H3N2 variant (H3N2v) in a resident of Ingham County. Influenza A H3N2v is different from highly pathogenic avian influenza A (H5N1) that has recently impacted dairy and poultry farms. Influenza A H3N2v is often associated with pigs or swine, though the source of this person’s exposure is still under investigation.

The individual tested positive for influenza A H3N2v in late July. The specimen was forwarded to the MDHHS Bureau of Laboratories for enhanced influenza virus sequence monitoring as part of the Centers for Disease Control and Prevention’s Emerging Infections Program where it again tested presumptive positive for influenza A H3N2v; later confirmed by the Centers for Disease Control and Prevention.

“While we believe this is an isolated case, Michigan residents should monitor for flu-like symptoms: fever, respiratory symptoms like cough and runny nose and body aches,” said Dr. Natasha Bagdasarian, chief medical executive. “If you have these symptoms, we recommend taking a test for influenza as well as COVID-19. Home COVID-19 tests are widely available, and both flu and COVID-19 tests are available at many pharmacies, urgent cares and clinics. Regardless of test results, please stay at home until you have recovered.”

“As our partners continue to investigate this case, the Michigan Department of Agriculture and Rural Development is ready to assist if any connections are made to an ill animal," said Tim Boring, director Michigan Department of Agriculture and Rural Development director. “As part of our state’s One Health approach, our agencies are committed to collaborative action protecting both animal and public health.”

Emergency department visits for influenza in Michigan are currently low and MDHHS anticipates that risks of influenza A H3N2v to the general public are low. While the infection was not linked to known exposure to swine or other animals, MDHHS reiterates precautions the public can take to avoid potential exposure at farms, fairs and exhibits:

• Refrain from eating or drinking in livestock barns or show rings.
• Do not take toys, pacifiers, cups, baby bottles, strollers or similar items into pig areas.
• Anyone who is at high risk of serious flu complications and planning to attend a fair should avoid pigs and swine barns.
• Wash hands often with soap and water. If soap and water are not available, use an alcohol-based hand rub.
• Avoid touching your eyes, nose and mouth. Germs spread this way.

While most individuals recover from influenza, including illnesses from variant viruses like H3N2v, these infections can sometimes cause severe disease, even in healthy people. If someone experiences respiratory symptoms, they should share any recent exposure to livestock with their doctor so that influenza testing can be considered. The same antiviral drugs used to treat seasonal flu can be used to treat H3N2v in children and adults. These treatments are most effective when taken early in the illness.

For more information, visit CDC.gov/swineflu.

It is probably no accident that the two novel swine flu viruses reported this week have come from the two states in the country (Colorado & Michigan) that are currently doing the most aggressive testing for H5N1.   

As we've seen previously (see UK Novel Flu Surveillance: Quantifying TTD), passive surveillance is apt to miss a lot of cases. 

This is the 3rd report of H3N2v we've from Ingram County over the past dozen years (see 2012's Michigan Reports Their First H3N2v Case and 2016's Michigan H3N2v Cases Rise To 8). 

The 2016 outbreak was significant, as 18 cases were identified across 2 states (Michigan & Ohio), and 16 of those cases were caused by a reassorted virus, one with an HA gene not previously seen in swine.  

We looked at several reports on the investigation, including MMWR: Investigation Into H3N2v Outbreak In Ohio & Michigan - Summer 2016, which found:

What is added by this report? 

In August 2016, 18 laboratory-confirmed infections with H3N2v virus were reported among persons who had attended agricultural fairs in Michigan and Ohio. Sixteen of the 18 cases occurred in persons who were infected with a reassortant H3N2v virus that contained a hemagglutinin (HA) gene previously not detected in variant viruses. The HA gene was likely introduced from humans into swine in 2010 or 2011, and viruses with this gene have circulated and evolved in swine to be genetically and antigenically different from both previous and currently circulating human seasonal influenza A(H3N2) viruses. 

What are the implications for public health practice? 

To minimize transmission of influenza viruses from swine to humans and from humans to swine, agricultural fair organizers should consider measures such as shortening the time swine are on the fairgrounds to ≤72 hours, immediately isolating ill swine, maintaining a veterinarian on call for the duration of the swine exhibition, providing prominent handwashing stations, and prohibiting food and beverages in animal barns. Persons at high risk for influenza-associated complications should be discouraged from entering swine barns.

The following year, we looked at EID Journal: Transmission Of Swine H3N2 To Humans At Agricultural Exhibits - Michigan & Ohio 2016, which noted that while widespread illness in pigs was only rarely reported, surveillance revealed an average prevalence of influenza A in fair pigs of 77.5%.

That study cautioned that `that subclinical influenza A infections in pigs remain a threat to public health (3).'

To put things in perspective, yesterday the CDC issued an IRAT (Influenza Risk Assessment Tool) report on the Texas H5N1 virus, which gave it an emergence score of 5.8, considerably lower than their 2019 assessment of the H3N2v (6.6) which emerged in 2016. 

In 2017, the last year to report a large number of H3N2v infections, the CDC reported `. . . sixty-two human infections with influenza A(H3N2)v virus were reported from nine different states and were closely related to the viruses detected in human infections in 2016 [2, 3].

Since then, only 11 H3N2v cases have been reported to the CDC.  It will be interesting to see how closely this Michigan case matches the 2016 strain. 

While IRAT can't predict which virus will become a pandemic strain (or when), it can help planners decide which viruses pose the greatest risks, so they can prioritize their efforts and investments.

And it should also remind us that H5N1 isn't the only game in town.