University of Michigan Flu Outbreak Identified as Influenza A Virus—Here’s What to Know

More than 500 people at the university’s Ann Arbor campus have been diagnosed with the flu—and the majority did not receive the flu vaccine.

The recent developments at the University of Michigan have garnered attention due to the disclosure by university authorities that an influenza outbreak is under investigation by the Centers for Disease Control and Prevention (CDC).

According to an official press release dated November 15, a significant and abrupt surge in flu instances has been observed among students on the Ann Arbor campus. The outbreak’s onset was marked by the identification of the initial positive flu case on October 6. Subsequent to this, the University Health Service has diagnosed a total of 528 cases of flu as of Monday. Notably, 77% of these cases were reported in individuals who had not received the current year’s flu vaccine.

The escalation of cases has transpired swiftly in recent weeks, with 313 positive cases identified during the week commencing November 8, and 198 cases detected in the preceding week. Notably, the percentage of positive cases from testing has reached a peak of 37%, indicating that a substantial proportion of individuals exhibiting flu-like symptoms indeed tested positive for the virus.

Enter the stage, the CDC. University authorities have revealed that a team of health experts from the Centers for Disease Control and Prevention (CDC) has stepped in with the intent of delving into the intricacies of the flu’s transmission dynamics and the efficacy of the flu vaccine. This investigation assumes particular significance as the nation braces itself for the forthcoming flu season.

Lindsey Mortenson, the medical director of University Health Services, underlined the swift identification of the cases as infections caused by the influenza A(H3N2) virus. In her statement issued on November 15, Mortenson emphasized the collaborative partnership with the CDC, noting that this collaboration will expedite the comprehension of how the current flu season might unfold both regionally and nationally, particularly within the context of the ongoing COVID-19 pandemic.

In light of these developments, a cascade of inquiries arises concerning the factors driving the extensive propagation of influenza A on the University of Michigan campus over a notably condensed timeframe. To address these curiosities, here is a concise breakdown of pertinent information.

What is influenza A—and how is it different than other influenza viruses?

Taking a step back for a moment, it’s important to recognize that the landscape of influenza encompasses four distinct virus types—A, B, C, and D. However, it’s the human influenza A and B viruses that primarily drive the annual flu seasons experienced during the winter months in the United States, as explained by the CDC. Influenza C viruses typically result in mild symptoms and lack the potential for epidemic outbreaks, while influenza D viruses are primarily associated with cattle infections.

The classification of influenza A and B viruses involves various subtypes. Within the domain of influenza A, these subtypes are categorized based on two surface proteins of the virus: hemagglutinin (H) and neuraminidase (N), elucidates the CDC. This classification entails 18 distinct hemagglutinin subtypes and 11 different neuraminidase subtypes, labeled as H1 through H18 and N1 through N11.

The phenomenon known as “reassortment” is relevant to these viruses, wherein genetic segments are exchanged between flu viruses. This dynamic process engenders a diverse array of influenza A variants that can circulate. Nevertheless, it’s worth noting that the subtypes H1N1 and H3N2, with the latter being responsible for the University of Michigan outbreak, constitute the most prevalent influenza A viruses affecting humans, as affirmed by the CDC.

In contrast, influenza B viruses are segregated into two lineages—B/Yamagata and B/Victoria.

“Influenza A and B represent distinct strains of the virus, each characterized by unique genetic attributes,” explains Amesh A. Adalja, MD, an expert in infectious diseases and a senior scholar at the Johns Hopkins Center for Health Security.

In terms of prevalence, influenza A largely dominates. Research published in the journal PLOS One in 2016 indicated that influenza A accounts for approximately 75% of flu cases, while the remaining 25% are attributed to influenza B. CDC data corroborates that the 2018–2019 flu season was primarily influenced by influenza A, particularly with influenza A(H1N1pdm09) during the early phase and influenza A(H3N2) taking precedence later.

Drawing a comparison between the two strains, Richard Watkins, MD, an infectious disease specialist and professor at the Northeast Ohio Medical University, emphasizes that “influenza B is generally associated with milder symptoms.” This sentiment is echoed by William Shaffner, MD, an infectious disease specialist and professor at the Vanderbilt University School of Medicine, who points out that influenza B typically doesn’t lead to significant outbreaks. He notes that influenza B tends to persist at a consistent level and becomes more prominent towards the conclusion of the influenza season.

However, it’s essential to recognize that exceptions exist, as evidenced by the 2019–2020 flu season. CDC data reveals that this season featured two distinct waves of flu activity, commencing with influenza B viruses. Dr. Shaffner underscores the unusual nature of this season, highlighting that influenza B defied expectations and deviated from its usual behavior by “starting early and causing outbreaks.”

What are the symptoms of influenza A?

Although influenza A and B represent distinct strains within the influenza virus family, their clinical presentations share remarkable similarities. “In terms of clinical manifestation, differentiating between influenza A and influenza B is not feasible,” highlights Dr. Schaffner. This means that even if an individual were to exhibit flu-like symptoms and seek medical attention, healthcare professionals would not be able to determine the specific flu type without resorting to additional testing via a rapid influenza diagnostic test (RIDT). However, it’s important to note that these tests might not consistently distinguish between influenza A and B. Furthermore, if they are able to identify the influenza type, they are unable to specify the exact subtype, as outlined by the CDC.

Fundamentally, “the symptoms of influenza remain consistent, regardless of the virus responsible for the infection,” explains Dr. Schaffner. Both influenza A and B can give rise to a constellation of symptoms that encompass:

• Fever
• Muscle aches
• Chills and sweating
• Headache
• Persistent, dry cough
• Shortness of breath
• Fatigue and weakness
• Congested or runny nose
• Sore throat
• Eye discomfort
• Vomiting and diarrhea (more prevalent in children compared to adults)

In essence, whether it’s influenza A or B, the symptomatology of the infection largely overlaps, underlining the challenge of visually distinguishing between the two without the aid of diagnostic tests.

How can you prevent or treat influenza A?

As you might anticipate, the most proactive measure against influenza A—and likewise for influenza B—is to prioritize receiving your annual flu vaccine. “These vaccines offer protection against diverse strains of both influenza A and influenza B,” emphasizes Dr. Schaffner.

To delve into specifics, the CDC has outlined the composition of this year’s flu vaccine, safeguarding against various influenza types and subtypes:

For vaccines produced using eggs:

• A/Victoria/2570/2019 (H1N1) pdm09-like virus
• A/Cambodia/e0826360/2020 (H3N2)-like virus
• B/Washington/02/2019-like virus (B/Victoria lineage)
• B/Phuket/3073/2013-like virus (B/Yamagata lineage)

For vaccines produced using cell- or recombinant-based methods:

• A/Wisconsin/588/2019 (H1N1) pdm09-like virus
• A/Cambodia/e0826360/2020 (H3N2)-like virus
• B/Washington/02/2019-like virus (B/Victoria lineage)
• B/Phuket/3073/2013-like virus (B/Yamagata lineage)

Furthermore, in the pursuit of minimizing your likelihood of contracting either influenza A or B, Dr. Schaffner underscores the importance of wearing masks in public and adhering to meticulous hand hygiene practices.

Should you, unfortunately, fall victim to influenza A, it’s valuable to recognize that its treatment aligns with that of influenza B, as highlighted by Dr. Watkins. In such cases, medical practitioners may prescribe antiviral medications like oseltamivir phosphate (commonly known as Tamiflu), zanamivir (Relenza), peramivir (Rapivab), or baloxavir marboxil (Xofluza). According to the CDC, the optimal efficacy of these flu antiviral drugs is achieved when initiated within the first two days of symptom onset. However, they may still offer benefits even if initiated beyond that timeframe, particularly for individuals at a heightened risk of severe flu complications.

Typically, these medications are recognized to mitigate fever, alleviate flu symptoms, and even curtail the duration of illness by at least a day, in accordance with the CDC. Irrespective of whether antiviral treatment is pursued or not, the CDC recommends that individuals with the flu remain home for a minimum of 24 hours after their fever has subsided without the use of fever-reducing medications.

According to the CDC’s guidance, a majority of individuals who contract the flu will naturally recuperate within a span of a few days to two weeks. Nevertheless, if you encounter more severe manifestations of the flu—such as breathing difficulties, intense muscle pain or weakness, or seizures—it’s imperative to promptly seek out emergency medical assistance.