Report on the week ending April 26 2013
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%
- 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
- 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
- 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
- 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
- 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