Influenza Update


Influenza declining


Influenza activity is declining in Wisconsin.  As of March 23, 2019, there had been 2,760 influenza-related hospitalizations since September 1, 2018; 50% of hospitalizations have been in individuals age ≥ 65 years; 472 individuals have been admitted to ICUs (41% with age ≥ 65 years) and 133 have required mechanical ventilation (39% with age ≥ 65 years).

The prevalence of influenza-like illness [fever of 100 degrees Fahrenheit or higher and either cough or sore throat] in Wisconsin's primary care patients is 2.4% and is declining.

7.7% of last week's primary care patients had all-cause respiratory infections.

The prevalence of acute diarrheal illness (ADI) in Wisconsin's primary care patients is at 1.6%; the most common pathogen is norovirus.

Primary Care Snapshot

The most commonly identified viral cause of acute respiratory infections (ARI) in Wisconsin is Influenza A. Over the past 4 weeks the typical ARI case presenting for primary care has 34.7 years old and 58% of patients have been female.  61% of patients identified a sick contact 1-to-3 days before illness onset and typically present to the clinic 3.7 days after illness onset.  21% of illnesses are characterized as mild, with 67% having moderate symptoms and 10% having severe symptoms. 

The typical symptoms reported include:

Typical SymptomsPercentViruses in CirculationPercent
fever65Influenza A60
cough86Influenza B2
sore throat60Coronavirus16
nasal congestion62RSV0
nasal discharge64Parainfluenza3

Clinical Notes


  • Influenza vaccine is recommended universally - keep vaccinating, as ~13.2% of cases are yet to com, everyone over the age of 6 months, including pregnant women
  • Pneumococcal vaccine PPSV23 is indicated for smokers, people with asthma and other chronic lung conditions as well as a number of other chronic conditions
  • ACIP routinely recommends PCV13 for individuals 65 years and older PPSV23 should be given 12 months after PCV13


  • Performance of Rapid Influenza Diagnostic Tests (RIDTs) depends on age and time from symptom onset
    • Higher sensitivities are attained at younger ages and within the first 3 days of symptoms
    • Clinical judgement is essential in diagnosis
  • Influenza infections are at low levels at this time
  • PPV of rapid antigen tests at this time is high
  • NPV of rapid antigen tests at this time is high


Antivirals need to be started within 48 hours of symptom onset to be effective against influenza.
Antivirals started after 48 hours may be effective for hospitalized patients with confirmed influenza.

Resistance Patterns

  • 634 influenza A[H3N2], 898 influenza A[H1N1] and 213 influenza B viruses have been tested. Three A[H1N1] viruses (0.3%) were resistant to oseltamivir and peramivir, but not zanamivir.
  • High levels of adamantane antiviral resistance exist in influenza A isolates from around the world. Adamantanes include amantadine and rimantadine; they are ineffective for influenza B.


  • Rhinoviruses, coronaviruses and human metapneumovirus are co-circulating across Wisconsin. RSV activity is declining.

Across the US:

5,324 (18.1%) respiratory specimens during week 13 (March 24-30) were positive for influenza.

For the 2018-2019 season to date (last week):

  • 96.0% (92.8%) of subtyped isolates have been type A
    • 39.5% (73.6%) of A viruses have been H3N2
    • 60.5% (26.4%) of all sub-typed A viruses have been 2009 H1N1
  • 4.0% (7.2%) of isolates have been type B
    • 44.9% (25.0%) were of the Yamagata lineage (not in the trivalent vaccine)
    • 55.1% (75.0%) were of the Victoria lineage
  • 7.2% of deaths during week 12 (March 17-23) were due to pneumonia or influenza [at the seasonally-adjusted epidemic threshold of 7.2%]

  • Five additional pediatric deaths were reported last week. 82 pediatric deaths have been reported this season due to influenza; 39 deaths were due to influenza A[H1N1], nine due to A[H3N2], 29 due to an influenza A virus for which no sub-typing was performed, and five due to influenza B.

Global News (from the WHO/CDC):

Measles Alert

From January 1 to April 4, 2019, 465 individual cases of measles have been confirmed in 19 states. The states that have reported cases to CDC are Arizona, California, Colorado, Connecticut, Florida, Georgia, Illinois, Indiana, Kentucky, Massachusetts, Michigan, Missouri, Nevada, New Hampshire New Jersey, New York, Oregon, Texas, and Washington.


As the Democratic Republic of the Congo Ebola outbreak is unfolding in a war zone, security incidents and pockets of community resistance continue to impact civilians and front line workers, requiring the response to continually adapt to the situation. This is now the 2nd largest Ebola outbreak in history.

Latest numbers as of 3 April 2019

Total cases: 1186 (confirmed = 1120, probable cases = 66)
Deaths: 751 (confirmed = 685, probable deaths = 66)

Case Fatality Rate: 63.3%

* The weekly influenza update is adapted from an email from Jon Temte, MD, PhD; Chair, Wisconsin Council on Immunization Practices; Professor, Department of Family Medicine and Community Health, University of Wisconsin School of Medicine and Public Health.

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