Community Validation of Influenza-like Illness as a Predictor of Influenza

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Community Validation ofInfluenza-like Illness
as a Predictor of Influenza

• Jonathan L. Temte, MD/PhD Alexis Eastman,
  MS-2
• University of Wisconsin School of Medicine and
  Public Health
• Peter A. Shult, PhD, Carol J. Kirk Mary
  Wedig
• Wisconsin State Laboratory of Hygiene
• Madison, Wisconsin

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Influenza-like Illness

• Definition
• Fever of 100oF (37.8oC) or higher
• Cough and/or Sore Throat
• Not due to any other illness
• Utility
• Simple and elegant
• Clinically relevant
• Easily ascertained

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ILI uses

• Community surveillance of influenza

• Clinical identification of influenza infection
• High PPV from research protocols
• Adults
• Children

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Factors Affecting Symptoms
Host Factors
Viral Factors
Age
Viral Strain
Immune Status
Viral Subtype
Underlying Disease
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Purpose of Study

• Review the contents of a large database
• Surveillance data emerging from a partnership
  between a public health laboratory and primary
  care clinicians
• Symptoms and virus identification
• Validate ILI for influenza infection
• Communitynot researchperspective

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The Surveillance Database

• Partnership of WSLH and UW-DFM since 1994
• Major modification of symptom check off in 1997
• Opportunistic sampling with fee-exempt virus
  culture
• physicians obtain specimens, record demographic
  and symptom data, sample is transported to WSLH
  by courier.
• Standard culture methods with isolation rate
  45
• Limited, de-identified data used
• 1997-2007
• IRB approved
• 3,796 episodes of acute respiratory illness care
  available

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Preferential Collection fromChildren and Young
Adults
Range 0 103 years 55.6 female
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PredictorsWorking definition of ILI

• FCorST
• F Fever on symptom checklist
• No requirement for level or documentation
• CorST Cough and/or Sore Throat
• sFCorST (includes seasonality)
• December through March
• Period with gt 90 of influenza cases

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Outcomesinfluenza isolation

• Paradigm 1 clinical primary care
• Influenza () vs. all other specimens
• Influenza 1230
• Non-influenza no virus isolated 2566
• Paradigm 2 ideal virus capture
• Influenza () vs. non-influenza virus ()
• Influenza 1230
• Non-influenza 523

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Distribution of outcomes
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Distribution of outcomes
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Performance Characteristics
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Additional Fiddlingassessing effects of age

• Concentrate on seasonal data
• Clinician informed by surveillance
• Concentrate on virus () specimens
• Symptomatic patient
• Early in illness
• Collection technique good
• Concentrate on age categories
• 0-4
• 5-24
• 25-64
• 65

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Effects of age(reference age 25-64
years)Binary logistic regression via Minitab
Release 13.1
Plt0.001
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What about little kids?the percent of ILI cases
due to
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Conclusions

• ILI (FCorST) performs well
• Public health tool for surveillance
• Early detection of influenza
• High sensitivity ( 0.88)
• Limited by low specificity (0.40)
• but fined tuned by virological methods
• ILI (sFCorST) performs well
• Clinician tool for diagnosis of influenza
• Informed by public health surveillance
• High PPV (0.84) moderate NPV
• Excluding young children raises PPV to 0.90

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Conclusions

• Influenza is the primary cause of ILI in patients
  age 5 years
• Many viruses can cause ILI in children 0-4 years
  of age. ILI should not be used for diagnosis
  alone in this group.
• ILI for predicting influenza infection has been
  validated in a primary care, community-based
  population

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Final Words

• If influenza is in the community and your patient
  is over 4 years old
• Is it influenza?
• FCorST

Of Course
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Acknowledgements

• Wisconsin Primary Care Clinicians
• UW-DFM residency clinics
• Numerous private physicians
• UW-DFM Summer Student Research and Clinical
  Assistantship Program
• Ms. Alexis Eastman
• Wisconsin State Laboratory of Hygiene

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Additional Material
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Basic Characteristics of Surveillance System

• Mean age of patient 26.6 years
• Range 0 to 103 years
• Sex
• Female 55.6
• Male 44.4
• Time between illness onset and collection
• Mean 3.86 days
• Median 2 days
• Rate of virus isolation 44.6

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Specimens Collected duringRespiratory Virus
Season
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Collection Day(Monday through Thursday Preferred)
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Most SpecimensCollected at Optimal Time
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Percent of Specimens with Positive Virus
Isolation