Avian Flu Diary: MMWR: H3N2v Outbreak At Three Fairs

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#13,623

2017 saw the second highest yearly number of swine variant influenza infections (n=67) reported to the CDC, which was only surpassed by 2012's 309 cases. Infections were nearly all associated with attendance of state fairs where pigs were being shown, most were H3N2v, and human infection was reported from 10 states.

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.

Maryland, with 39 confirmed cases, saw the most cases (see FluView Week 38: 32 Presumptive & Confirmed H3N2v Cases). This recap from the CDC.

A total of 67 variant virus infections have been reported to CDC during 2017. Sixty-two of these have been A(H3N2)v viruses (Delaware [1], Iowa [1], Maryland [39], Michigan [2], Nebraska [1], North Dakota [1], Ohio [15], Pennsylvania [1], and Texas [1]), one was an influenza A(H1N1) variant [A(H1N1)v] (Iowa [1]) virus, and four were influenza A(H1N2) variant [A(H1N2)v] viruses (Colorado [1] and Ohio [3]). Six of these 67 infections resulted in hospitalization; all patients have recovered.

This year the number of reported cases has dropped (n=13), and the main subtype reported has switched to H1N2v (see CDC FluView: Four More Cases Of H1N2v Reported (CA, OH)).

Today, the CDC's MMWR has published a detailed overview of the 2017 Maryland outbreak. I've only included some excerpts, so follow the link to read it in its entirety.

Influenza A(H3N2) Variant Virus Outbreak at Three Fairs — Maryland, 2017
Weekly / October 26, 2018 / 67(42);1169–1173

Monique M. Duwell, MD1,2; David Blythe, MD2; Michael W. Radebaugh, VMD3; Erin M. Kough, MPH2; Brian Bachaus, MS2; David A. Crum, DVM2; Keith A. Perkins Jr.2; Lenee Blanton, MPH4; C. Todd Davis, PhD4; Yunho Jang, PhD4; Amy Vincent, DVM, PhD5; Jennifer Chang, PhD5; Dianna E. Abney, MD6; Lisa Gudmundson7; Meenakshi G. Brewster, MD8; Larry Polsky, MD9; David C. Rose, MD10; Katherine A. Feldman, DVM2 (View author affiliations)

On September 17, 2017, the Maryland Department of Agriculture (MDA) was notified by fair and 4-H officials of ill swine at agricultural fair A, held September 14–17. That day, investigation of the 107 swine at fair A revealed five swine with fever and signs of upper respiratory tract illness. All five respiratory specimens collected from these swine tested positive for influenza A virus at the MDA Animal Health Laboratory, and influenza A(H3N2) virus was confirmed in all specimens by the U.S. Department of Agriculture National Veterinary Services Laboratory (NVSL).

On September 18, MDA was notified by fair and 4-H officials that swine exhibitors were also ill. MDA alerted the Maryland Department of Health (MDH). A joint investigation with MDH and the local health department was started and later broadened to Maryland agricultural fairs B (September 13–17) and C (September 15–23). In total, 76 persons underwent testing for variant influenza, and influenza A(H3N2) variant (A(H3N2)v) virus infection was identified in 40 patients with exposure to swine at these fairs (Figure), including 30 (75%) who had more than one characteristic putting them at high risk for serious influenza complications; 24 (60%) of these were children aged < 5 years. Twenty-six (65%) patients reported direct contact with swine (i.e., touching swine or swine enclosure), but 14 (35%) reported only indirect contact (e.g., walking through a swine barn). Two children required hospitalization; all patients recovered.

This outbreak highlights the risk, particularly among children, for contracting variant influenza virus at agricultural fairs after direct or indirect swine contact. Publicizing CDC’s recommendation that persons at high risk for serious influenza complications avoid pigs and swine barns might help prevent future variant influenza outbreaks among vulnerable groups (1).

(SNIP)

Acknowledgments

Dianna D. Carroll, PhD, Division of Scientific Education and Professional Development, Center for Surveillance, Epidemiology, and Laboratory Services, CDC; Richard B. Brooks, MD, Division of Healthcare Quality Promotion, CDC; staff members in the Maryland Department of Health Laboratories Administration; staff members in the health departments in the Maryland counties of Charles, Frederick, St. Mary’s, Calvert, and Anne Arundel; staff members in the U.S. Department of Agriculture National Veterinary Services Laboratories.

Summary

What is already known about this topic?

Outbreaks of variant influenza have occurred in agricultural fair settings in the United States.

What is added by this report?

In September 2017, 40 cases of influenza A(H3N2) variant virus infection were identified among persons with swine exposure at one of three Maryland agricultural fairs. Thirty cases (75%) occurred among persons at high risk for serious influenza complications. Thirty-five percent of patients reported only indirect swine contact.

What are the implications for public health practice?

Increased public education that groups at high risk for influenza complications should avoid pigs and swine barns is needed. When swine influenza virus is detected at one fair, enhanced surveillance should extend to all fairs in the region.

While swine variant flu infections in humans have been generally mild or moderate, some people have required hospitalization, and we've seen some deaths. The CDC's general risk assessment of these swine variant (H1N1v, H1N2v, H3N2v) 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

And to raise general awareness, particularly among young people, this summer the CDC - in conjunction with the USDA and 4H - released an ambitious 60-page graphic novel on swine variant flu and how disease detectives investigate outbreaks.