Avian Flu Diary: Michigan DOH Announces A Novel Swine Variant H1N2v Infection Linked To A County Fair

Credit CDC

#17,003

After a pronounced hiatus during the opening two years of the pandemic - when most county and state fairs were shuttered - we've seen a resurgence in swine variant flu infections across the country as fairs have reopened this summer.

Since early August - and including today - we've seen 6 cases reported; three H3N2v infections from West Virginia and three H1N2v cases (1 each from Ohio, Oregon, and Michigan).

Up until about 5 years ago, H1N2v was the least common swine variant virus reported n the United States . Since the 2017-18 flu season it has become the most common variant, accounting for just over 50% of cases.

Most (but not all) swine variant infections are mild or moderate, self-limiting, and are clinically indistinguishable from regular seasonal influenza.

Since most people never see a doctor or get tested for uncomplicated `flu-like symptoms' (see pyramid graphic at top of blog), it is assumed that swine variant infections are more common than the reports we get would indicate.

During a small outbreak of H3N2v (n=13) a decade ago, researchers estimated that fewer than 1 in every 200 cases was identified (see CID Journal: Estimates Of Human Infection From H3N2v (Jul 2011-Apr 2012).

Results. We estimate that the median multiplier for children was 200 (90% range, 115–369) and for adults was 255 (90% range, 152–479) and that 2055 (90% range, 1187–3800) illnesses from H3N2v virus infections may have occurred from August 2011 to April 2012, suggesting that the new virus was more widespread than previously thought.

The CDC's Assessment of the Risk from these viruses reads:

CDC Assessment

Sporadic infections and even localized outbreaks among people with variant influenza viruses may occur. All influenza viruses have the capacity to change and it’s possible that variant viruses may change such that they infect people easily and spread easily from person-to-person. The Centers for Disease Control and Prevention (CDC) continues to monitor closely for variant influenza virus infections and will report cases of H3N2v and other variant influenza viruses weekly in FluView and on the case count tables on this website

The details of the latest case from Michigan follow, after which I'll have a postscript.

Fairgoers reminded of precautions to take at events featuring swine exhibits

September 12, 2022

Influenza A H1N2 variant identified in Michigan resident with exposure to swine

LANSING, Mich. – The Michigan Department of Health and Human Services (MDHHS) has announced a human case of Influenza A (H1N2)v in the state. MDHHS and the Michigan Department of Agriculture and Rural Development (MDARD) are urging fairgoers to take precautions to prevent infection at upcoming fairs where swine may be exhibited.

The case was confirmed by the Centers for Disease Control and Prevention (CDC) on Sept. 9, in a Berrien County fairgoer who had contact with swine at the Berrien County Youth Fair. The fair was held Aug. 15-20. Fair officials are working collaboratively with MDHHS and the Berrien County Health Department.

Fair season in Michigan extends into October. The following are steps Michiganders can take to protect themselves and prevent the spread of any illness: Anyone who is at high risk of serious flu complications and is planning to attend a fair should avoid pigs and swine barns.
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.
Avoid touching your eyes, nose and mouth. Germs spread this way.
Avoid contact with pigs if you have flu-like symptoms. This includes being in a swine barn if you are ill as influenza can be spread via respiratory droplets.
If you are sick, stay home from work or school until your illness is over.
Avoid close contact with sick people.
Cover your nose and mouth with a tissue when you cough or sneeze. Throw the tissue in the trash after you use it and wash your hands.
Wash your hands often with soap and water. If soap and water are not available, use an alcohol-based hand sanitizer.
Swine influenza is a respiratory disease in pigs caused by type A influenza viruses that regularly circulate among swine. Swine influenza viruses do not usually infect humans, but human infections have been reported. People cannot get swine influenza from eating properly prepared pork or handling pork products – only from contact with an ill pig.

Symptoms of swine influenza in people are similar to the seasonal flu and can include fever, cough, runny nose, and sometimes body aches, nausea, vomiting or diarrhea. On rare occasions, swine influenza in humans can lead to severe diseases, such as pneumonia or death. Physicians are reminded to consider swine influenza in persons presenting with these symptoms, even during the warmer months when seasonal influenza cases are low.

(Continue . . . )

Swine variant influenza is admittedly a `sensitive' topic, particularly in the major pig producing states, which took an economic beating during and after the 2009 H1N1 `Swine flu' pandemic. While I appreciate their desire to reassure the public, I do take issue with the following statement, which is misleading at best.

People cannot get swine influenza from eating properly prepared pork or handling pork products – only from contact with an ill pig.

This statement is demonstrably `wrong' on several counts.

First, human-to-human transmission of swine variant viruses - while undoubtedly rare - does happen. We've seen a number of cases where the patient had no direct contact with pigs, including the Oregon case last month (see CDC FluView WK 32: Oregon Reports 4th Swine Variant (H1N2v) Case of 2022).

Second, a pig need not be `ill', only infected, in order to transmit the virus. According to one study (see Asymptomatic Pigs: Revisited) more than 80% of the pigs that tested positive for influenza at the Ohio State fair between 2009 and 2011 showed no signs of illness.

Third, it completely ignores the potential for fomite transmission, or via contaminated dust particles (see PLoS One: Concentration, Size Distribution, and Infectivity of Airborne Particles Carrying Swine Viruses).

For a fascinating anecdotal report on a housebound woman who lived 2 km downwind of a pig farm contracting a reassorted swine variant virus, you may wish to revisit EID Journal: Reassortant Influenza A(H1N1)pdm09 Virus in Elderly Woman, Denmark, January 2021.

The CDC's Key Points About Swine Variant Influenza discusses all three of these scenarios.

How are variant influenza viruses spread?

Influenza viruses can be directly transmitted from pigs to people and from people to pigs. These infections have most commonly been reported after close proximity to infected pigs, such as in pig barns and livestock exhibits housing pigs at fairs. Infected pig cough or sneeze and droplets with influenza virus in them can spread through the air. If these droplets land in your nose or mouth, or are inhaled, you can be infected. There also is some evidence that you might get infected by touching a surface with virus on it and then touching your mouth or nose. A third way to possibly get infected is to inhale droplets or dust containing influenza virus. Scientists aren’t really sure which of these ways of spread is the most common.

Human-to-human transmission of variant flu viruses also has occurred, though this method of spread has been limited. This kind of transmission is thought to occur in the same way that seasonal flu transmits in people, which is mainly through coughing or sneezing by people who are infected. People also may become infected by touching something with flu viruses on it and then touching their mouth or nose. It’s important to note that in most cases, variant flu viruses have not shown the ability to spread easily and sustainably from person to person.

All reasons why the CDC advises those who are at higher risk of serious flu complications (including children under 5, adults over 65, pregnant women, and those with certain chronic medical conditions), to avoid pigs and the swine barn altogether.

While the pandemic risk from swine variant viruses is currently thought to be low, these viruses continue to reinvent themselves as they circulate in pigs, and so we pay very close attention whenever they jump species to humans.

For more on this summer's swine variant uptick, you may wish to revisit: