Weekly Influenza Update

July 19, 2017


The 2017 city and county fair season in the Midwest is now underway. During recent summers, swine exhibitions at agricultural fairs and other direct or indirect exposure to swine have been associated with human infections caused by variant influenza A viruses that include A/H3N2v, A/H1N2v and A/H1N1v. So far this year, no human cases of variant influenza A have been detected in humans in the United States although swine flue has been detected in two Midwest states including Wisconsin.

Please see the attached request sent out through the Wisconsin Division of Public Health.

Wisconsin's influenza activity has declined to baseline, with 80% of recent detections being influenza B. There have been 3,861 influenza-related hospitalizations since September 1, 2016, with 450 admitted to ICU and 101 requiring mechanical ventilation. 67% of hospitalizations have been in individuals age 65 and older. Across the US one out of every 350 people age 65 and older has been hospitalized with laboratory-confirmed influenza.

The estimated prevalence of influenza-like illness [fever of 100 degrees F or higher and either cough or sore throat] in Wisconsin's primary care patients is at 1.3% and is stable.

7.2% 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%

Primary Care Snapshot

The most commonly identified viral causes of Acute Respiratory infections (ARI) in Wisconsin is rhinovirus/enterovirus. Over the past 4 weeks the typical ARI case presenting for primary care has been 33.5 years old and 70% of patients have been female. 44% of patients identified a sick contact 1-to-3 days before illness onset and typically present to the clinic 3.6 days after illness onset. 21% of illnesses are characterized as mild, with 68% having moderate symptoms and 11% having severe symptoms.

The typical symptoms reported include:

cough 84%
nasal congestion 56%
nasal discharge 58%
sore throat 68%
fever 61%
malaise 60%
headache 60%
myalgia 40%

Clinical Notes

Prophylaxis - It is reasonable to stop routinely vaccinating as of May 1st; continue to offer influenza vaccine to high-risk individuals.

There is a good match between this year's vaccine and circulating viruses. Vaccine effectiveness has been estimated at 48%.

  • Influenza vaccine is recommended universally for 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 moderate levels at this time
  • PPV of rapid antigen tests at this time is moderate
  • NPV of rapid antigen tests at this time is high


  • Oseltamivir is now available as a generic
  • See the CDC influenza antiviral medication summary for clinicians
  • 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

  • 2,099 influenza A[H3N2], 296 influenza A[H1N1] and 728 influenza B viruses have been tested. No viruses (0.0%) were resistant to oseltamivir, zanamivir or peramivir.
  • High levels of adamantene antiviral resistance exist in influenza A isolates from around the world. Adamantanes include amatadine and rimantadine; they are ineffective for influenza B.


  • Rhinoviruses/enteroviruses are the predominant non-influenza viruses in Wisconsin
  • RSV activity is at relatively low levels
  • Human metapneumovirus, parainfluenza, and coronaviruses are co-circulating at lower levels

Across the US: influenza is decreasing

938 (9.6%) respiratory specimens during week 17 (April 23-29) were positive for influenza.

For the 2016-2017 season to date (last week):

  • 71.4% (27.4%) of subtyped isolates have been type A
    • 97.2% (96.0%) of A viruses have been H3N2
      • 2.8% (4.0%) of all sub-typed A viruses have been 2009 H1N1
  • 28.6% (72.6%) of isolates have been type B
    • 70.7% (83.1%) of B viruses have been of the Yamagata lineage
      • 29.1% (16.9%) of B viruses have been of the Victoria lineage
  • 6.6% of deaths during week 15 (April 9-15) were due to pneumonia or influenza (above the seasonally adjusted epidemic threshold of 7.2%).
  • Six additional pediatric deaths were reported last week. 89 pediatric deaths have been reported this season. 40 deaths were associated with influenza A[H3]; two deaths were associated with influenza A[H1]; 17 deaths were associated with influenza A viruses for which no subtyping was performed; 30 deaths were associated with influenza B; and one death was associated with an influenza virus for which the type was not determined.

Global News (from the WHO/CDC):

Zika: 5,274 cases have been reported in the U.S. with 1,793 cases in pregnant women. Wisconsin has had 58 cases so far, all associated with travel.

For up to date information, visit the zika page on CDC.

* 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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