Weekly Influenza Update

Report on the week ending April 26 2013

Wisconsin

Influenza activity is at baseline levels in Wisconsin

The number of influenza cases is at baseline levels in Wisconsin.  Influenza B viruses account for about 77% of sporadic isolates in Wisconsin.  Since October 1st, over 2,923 individuals have been hospitalized due to influenza.  12% of these patients have been admitted to an ICU and 3% have required mechanical ventilation.  63% of hospitalizations have been for individuals aged 65 years and older.

The prevalence of influenza-like illness [fever of 100°F or higher and either cough or sore throat] in Wisconsin's primary care patients is estimated to be 0.6% and is stable.

• 11.6% 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 2.12%
• When the percent of primary care respiratory infection patients who have a recorded fever >100°F rises above 5%, there is high correlation with influenza in Wisconsin. The current level is 3%, indicating that we have moved out of the influenza outbreak.
  

Primary Care Snapshot

The most commonly identified viral cause of medically-attended Acute Respiratory infection (ARI) in Wisconsin is Influenza B.  Over the past 4 weeks the typical ARI case presenting for primary care has been 33.0 years old and 52% of patients have been female.  48% of patients identified a sick contact 1-to-3 days before illness onset and typically present to the clinic 4.4 days after illness onset.  30% of illnesses are characterized as mild, with 67% having moderate symptoms and 2% having severe symptoms.

Typical symptoms include:

• cough -  87%
• fever -  65%         
• nasal discharge - 63% 
• nasal congestion - 61% 
• sore throat -  61% 
• malaise -  57%
• headache -  43% 
• myalgia -  28%

Clinical Notes

Prophylaxis

• Influenza vaccine is recommended universally; as we continue to see sporadic cases-
  • continue to vaccinate through the end of April (everyone over the age of 6 months, including pregnant women)
• Pneumococcal vaccine is indicated for smokers, people with asthma and other chronic lung conditions as well as a number of other chronic conditions

Diagnosis

• Influenza infections are at low levels at this time
• Clinical diagnosis, based on fever and cough and/or sore throat, has low PPV for influenza.
• PPV of rapid antigen tests at this time is moderate
• NPV of rapid antigen tests at this time is high

Treatment

• Antivirals need to be started with 48 hours of symptom onset to be effective against influenza
  • oseltamivir may be used to treat children as young as 2 weeks old
• Antivirals started after 48 hours may be effective for hospitalized patients with confirmed influenza

Resistance Patterns

• Oseltamivir resistance has been detected in:
  • 0.4% (2/483) of influenza A(H1N1) isolates
  • 0.1% (2/1821) of influenza A(H3N2) isolates
  • No resistance in influenza B isolates
• There has been no resistance to Zanamivir
• High levels of adamantine resistance exist in influenza A isolates from around the world

Other

• RSV activity is declining in Wisconsin.
• Rhinoviruses and human metapneumoviruses are the predominate Wisconsin isolates from non-influenza, non-RSV patients with respiratory infection
• Coronaviruses and parainfluenza is circulating at lower levels in Wisconsin

Across the U.S.

354 (9.3%) respiratory specimens during week 15 (April 7-13) were positive for influenza.

For the 2012-2013 season to date (last week):

• 71.4% (26.3%) of subtyped isolates have been type A
• 3.9% (47.1%)) of all sub-typed A viruses have been 2009 H1N1
• 96.1% (52.9%) of A viruses have been H3N2
• 28.6% (73.7%) of isolates have been type B with 68.8% characterized as the Yamagata (vaccine) lineage
• 7.2% of deaths during week 15 (April 7-13, 2013) were due to pneumonia or influenza [below the seasonally-adjusted epidemic threshold of 7.4%]
• 10 additional pediatric deaths was reported this past week.
  
  • 126 pediatric deaths have been reported this season, including four from Wisconsin.
  • 48% (60/126) of deaths were associated with influenza A.
  • 51% (64/126) were associated with influenza B.
  • There was one death with dual (A+B) infection.

 The Weekly Influenza Update is adapted by WAFP from an email by Jon Temte, Chair, US Advisory Committee on Immunization Practic