Weekly Influenza Update

May 10, 2017

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 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 1.3% 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 [symptoms for influenza (+) patients are in brackets]:

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 U.S.: 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. 

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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