Weekly Influenza Update

April 20, 2017

Measles Alert
The Minnesota Department of Health announced on Friday April 14, 2017 five new cases of measles in Hennepin County, birnging the total number of cases to eight. Hennepin County includes the Minneapolis-St. Paul-Bloomington, MN-WI metropolitan area. The cases are in unvaccinated children ages 1-4 years and seven of the cases are Somali Minnesotan. Local health departments and tribal clinics should work with health care providers in their jurisdiction to raise awareness about the diesase and take immediate steps if there is a suspected or confirmed case. For additional information on measles, see the Wisconsin Department of Health Services website.

Influenza is declining. 
For treatment guidance, see the CDC website

As about 1.6% of cases are yet to occur and influenza continues to circulate, continue to vaccinate.

Wisconsin's influenza activity is declining, but with changing dominant types. 67% of recent detections have been Influenza B; 33% have been Influenza A. There have been 3,646 influenza-related hospitalizations since September 1, 2016, with 418 admitted to ICU and 95 requiring mechanical ventilation. This compares to 1,708 hospitalizations last year at this time, and 4,546 for the 2014-2015 season. 67% of hospitalizations have been in individuals age 65 and older. Influenza A[H3N2] is less kind to elders; across the US one out of every 375 people age ≥65 has been hospitalized with laboratory-confirmed influenza.

The estimated prevalence of influenza-like illness [fever of 100oF or higher and either cough or sore throat] in Wisconsin's primary care patients is at 1.7% and is stable.

8.4% 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 Influenza B.  Over the past 4 weeks the typical ARI case presenting for primary care has been 38.0 years old and 61% of patients have been female. 45% 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. 25% of illnesses are characterized as mild, with 67% having moderate symptoms and 8% having severe symptoms.

The typical symptoms reported include [symptoms for influenza (+) patients are in brackets]:

cough 93% [100%]
nasal congestion 58% [68%]
nasal discharge 74% [89%]
sore throat  58% [63%]
fever 53% [74%]
malaise 54% [68%]
headache  53% [63%]
myalgia 43% [53%]







Clinical Notes:

Prophylaxis - 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 moderately high
  • 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

  • 1,717 influenza A[H3N2], 261 influenza A[H1N1] and 626 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 are the predominant non-influenza viruses in Wisconsin
  • RSV activity is declining
  • Coronaviruses, human metapneumovirus, parainfluenza, and adenoviruses are co-circulating at lower levels

Across the U.S.: influenza is increasing

3,044 (15.2%) respiratory specimens during week 14 (April 2-8) were positive for influenza. 

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

  • 67.8% (25.9%) of subtyped isolates have been type A
    • 97.2% (88.5%) of A viruses have been H3N2
      • 2.8% (11.5%) of all sub-typed A viruses have been 2009 H1N1
  • 32.2% (74.1%) of isolates have been type B
    • 85.7% (84.5%) of B viruses have been of the Yamagata lineage
    • 14.3% (15.5%) of B viruses have been of the Victoria lineage

  • 7.1% of deaths during week 12 (March 19-25) were due to pneumonia or influenza (above the seasonally adjusted epidemic threshold of 7.4%).
  • Twelve additional pediatric deaths were reported last week. 72 pediatric deaths have been reported this season. 34 deaths were associated with influenza A[H3]; two deaths were associated with influenza A[H1]; 15 deaths were associated with influenza A viruses for which no subtyping was performed; 20 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: 5,238 cases have been reported in the U.S. with 1,762 cases in pregnant women. Wisconsin has had 56 cases so far, all associated with travel. 

See cdc.gov/zika for up to date information.

*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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