Influenza Surveillance
in the United States
Oliver Morgan, PhD MSc
Division of Emerging Infections and Surveillance Services
Dr. Lyn Finelli, Scott Epperson
Influenza Division
Centers for Disease Control and Prevention
Objectives of Influenza Surveillance
• Determine which influenza viruses are
circulating; where are they circulating; when are
they circulating
• Determine intensity and impact of influenza
activity
• Detect unusual events
– Infection by unusual viruses
– Unusual syndromes caused by influenza viruses
– Unusually large/severe outbreaks
Influenza Surveillance
• Responsibility for national influenza surveillance
rests with CDC
• State and local public health departments are
our primary partners
• Review of surveillance held in 2006 & 2007 with
Council of State and Territorial Epidemiologists
(CSTE)
– Build a system that is useful on the local level and
builds to national level surveillance
The Five Categories of Influenza Surveillance
•
•
•
•
•
Viral Surveillance
Mortality Surveillance
Hospitalization Surveillance
Outpatient Illness Surveillance
Summary of the Geographic Spread of Influenza
http://www.cdc.gov/flu/weekly/
The Five Categories of Influenza Surveillance
• Viral Surveillance
– WHO (World Health Organization) and NREVSS
(National Respiratory and Enteric Virus Surveillance
System) Collaborating Laboratories
– Novel influenza A virus surveillance
•
•
•
•
Mortality Surveillance
Hospitalization Surveillance
Outpatient Illness Surveillance
Summary of the Geographic Spread of Influenza
Viral Surveillance
• Viral surveillance is the foundation for influenza
control efforts
– Identify changes in circulating strains
• Future vaccine strain selection
• Assess current vaccine match
• Identify viruses with pandemic potential
– Establish seasonality
• Timing of active surveillance
• Timing of influenza control activities
Virologic Surveillance in the U.S.
• ~150 participating laboratories
– Specimens collected during routine patient care
– Weekly reports
• # specimens tested
• # positive for influenza: type, subtype, age
• Novel influenza A reporting
– Made nationally notifiable condition in 2007
U.S. Virologic Surveillance:
Participating Labs
• WHO Collaborating Labs
– ~ 85 labs
– Maintained by ID/CDC
– State health dept.,
universities, large tertiary
care hospital labs, and DoD
– Subtype influenza A
– Report age data
– Send subset of isolates to
CDC for further testing
• NREVSS labs
– ~ 65 labs
– Maintained by DVD/CDC
– Hospital labs
– Report data on other
respiratory viruses
– Less likely to subtype
influenza A viruses
– Don’t report age data
– Data incorporated into flu
surveillance since 97-98
Viral Strain Surveillance
• WHO labs submit subset of isolates to CDC
strain surveillance lab
• Detailed antigenic characterization
• Sequencing of some isolates
• Antiviral resistance testing
– Adamantanes - when needed
– Neuraminidase inhibitors - large subset
U.S. WHO/NREVSS Collaborating Laboratories
National Summary, 2008-09
4500
4000
3500
A (Pandemic H1N1)
A (Unable to Subtype)
A (H3)
A (H1)
A (Subtyping not Performed)
B
Percent Positive
55
50
45
40
3000
35
2500
30
2000
25
20
1500
15
1000
10
500
5
0
0
40 42 44 46 48 50 52 1
3
5
7
9 11 13 15 17 19 21 23 25 27 29 31 33 35
Week
The Five Categories of Influenza Surveillance
• Viral Surveillance
• Mortality Surveillance
– 122 Cities Mortality Reporting System
– Influenza-Associated Pediatric Deaths
• Hospitalization Surveillance
• Outpatient Illness Surveillance
• Summary of the Geographic Spread of Influenza
122 Cities Mortality Reporting System
• Purpose: monitor P&I related mortality in a timely
manner
• Weekly reports from vital statistics offices in 122 US
cities
– Total # of death certificates filed
– # with pneumonia or influenza listed anywhere
• ~ 1/4 of US deaths
Pneumonia and Influenza Mortality
for 122 U.S. Cities
10
% of All Deaths Due to P&I
Week Ending 07/04/2009
Epidemic Threshold
8
6
Seasonal Baseline
2005
2006
2007
2008
2009
4
21 30
40
50
10
20
30
40
50
10
20
30
40
Surveillance Weeks
50
10
20
30
40
50
10
20
Pediatric Influenza-Associated Mortality Reporting
• In June 2004, CSTE adopted proposal to make
influenza-associated death in a person <18 yrs. a
nationally notifiable condition.
– Reporting began in October 2004
– Data reported weekly in MMWR and FluView
Number of Influenza-Associated Pediatric Deaths
by Week of Death
Week ending 07/04/2009
12
11
10
8
7
6
5
4
3
2
1
2009-23
2009-17
2009-11
2009-05
2008-52
2008-46
2008-40
2008-34
2008-28
2008-22
2008-16
2008-10
2008-04
2007-50
2007-44
2007-38
2007-32
2007-26
2007-20
2007-14
2007-08
2007-02
2006-48
2006-42
2006-36
2006-30
2006-24
2006-18
2006-12
2006-06
2005-52
2005-46
0
2005-40
Number of deaths
9
Week of Death
Deaths Reported Current Week
Pandemic Influenza A (H1N1) Deaths Reported Current Week
Deaths Reported Previous Weeks
Pandemic Influenza A (H1N1) Deaths Reported Previous Weeks
The Five Categories of Influenza Surveillance
• Viral Surveillance
• Mortality Surveillance
• Hospitalization Surveillance
– Emerging Infections Program (EIP)
– New Vaccine Surveillance Network (NVSN)
• Outpatient Illness Surveillance
• Summary of the Geographic Spread of Influenza
Hospitalization Surveillance
• Population-based
surveillance for laboratory
confirmed influenza related hospitalizations
• Emerging Infections
Program
– All ages
– Lab tests as part of routine
patient care
– Chart reviews
• New Vaccine Surveillance
Network
– 0 – 4 year olds
– Children admitted with fever
or acute respiratory illness
are swabbed and tested
– Culture and PCR
– Chart reviews
The Five Categories of Influenza Surveillance
•
•
•
•
Viral Surveillance
Mortality Surveillance
Hospitalization Surveillance
Outpatient Illness Surveillance
– U.S. Influenza Sentinel Provider Surveillance Network
(ILINet)
• Summary of the Geographic Spread of Influenza
Outpatient Influenza Surveillance (ILINet)
• ~2,400 healthcare providers in 50 states
• Weekly reports
– Total # of patient visits
– # visits for influenza-like illness (ILI) by age group
• ILI = fever  100 ºF (37.8 ºC) and cough or
sore throat, in absence of a known cause other
than influenza
• Early, peak, and late season
Percentage of Visits for Influenza-like Illness (ILI)
Reported by ILINet
7
Week ending 07/04/2009
6
% of Visits for ILI
5
4
3
2
1
0
40
42
44
46
48
50
52
1
3
5
7
9
11
13
15
17
19
21
23
Surveillance Week
2006-07*
2007-08*
2008-09
National Baseline
Note: There was no week 53 during the 2006-07 and 2007-08 seasons, therefore the week 53 data point for
those seasons is an average of weeks 52 and 1.
25
The Five Categories of Influenza Surveillance
•
•
•
•
•
Viral Surveillance
Mortality Surveillance
Hospitalization Surveillance
Outpatient Illness Surveillance
Summary of the Geographic Spread of Influenza
Geographic Spread of Influenza
• Weekly reports from State and territorial
epidemiologists
• Assessment of overall influenza activity at state
level
– None, sporadic, local, regional, or widespread
– Incorporates virologic and ILI data
– Only system reporting state-level data
• Allows local interpretation of surveillance data
Influenza Surveillance Challenges
• Not everyone with influenza accesses healthcare
• Can’t distinguish influenza from other respiratory
viruses on clinical criteria
– Most cases are not tested / lab confirmed
• Volume – can’t test all respiratory cases
• Not all cases will test positive
– Many cases with severe influenza-related complications
(hospitalization or death)
– Timing of sample collection not optimal
• Surveillance reports must be timely
Goals of Pandemic
Influenza Surveillance
1.
2.
3.
4.
5.
6.
Identify and track viruses/strains
Describe clinical infections
Determine who is affected and the severity of the
pandemic
Detect the onset and duration of the pandemic and
the geographic spread
Guide interventions
Provide information to partners
Pandemic Influenza
Intervals
C
Initiation
A
Investigation
B
Recognition
D
Acceleration
E
Peak
Transmission
F
Deceleration
G
Resolution
Pandemic Surveillance Framework
• Pandemic intervals as framework
• Develop interval-specific surveillance strategy based on
information we need for action
• Use combinations of surveillance systems to collect the
data necessary to address the goals of surveillance for
each interval
• Feasible and sustainable approach to pandemic
surveillance
C
A
D
E
F
G
B
Interval A
Investigation
Interval A
Triggers
Identification of human cases
of novel influenza A
Federal Actions
Maintain surveillance
Support investigation/containment
Characterize viruses
Reporting
Frequency
WHO & NREVSS Collaborating
Laboratories
Weekly
Novel Influenza A Virus Infections
Daily
122 Cities Mortality Reporting
System
Weekly
Influenza Associated Pediatric
Mortality
Daily
EIP Influenza Surveillance Network
Bi-Weekly
New Vaccine Surveillance Network
Bi-Weekly
State and Territorial Epidemiologists
Report
Weekly
Sentinel Provider Surveillance
Network
Weekly
Aggregate case reporting
NR
C
A
D
E
F
G
B
Interval B
Recognition
Interval B
Triggers
Confirmation of human cases and
demonstration of efficient and
sustained human to human
transmission
Federal Actions
Maintain surveillance
Deploy responders
Evaluate case fatality ratio and PSI
Reporting
Frequency
WHO & NREVSS Collaborating
Laboratories (subset)
Daily
Novel Influenza A Virus Infections
Daily
122 Cities Mortality Reporting
System (web-based)
Daily
Influenza Associated Pediatric
Mortality
Daily
EIP Influenza Surveillance Network
Bi-Weekly
New Vaccine Surveillance Network
Bi-Weekly
State and Territorial Epidemiologists
Report
Weekly
Sentinel Provider Surveillance
Network (subset)
Daily
Aggregate Case Reporting
NR
C
A
D
E
F
G
B
Interval C
Initiation
Interval C
Triggers
Laboratory confirmed human cases
detected in any state
Federal Actions
Maintain surveillance
Conduct lab confirmation and
characterize viruses
Deploy responders/SNS
Evaluate case fatality ratio and PSI
Reporting
Frequency
WHO & NREVSS Collaborating
Laboratories (subset)
Daily
Novel Influenza A Virus Infections
Daily
122 Cities Mortality Reporting
System (web-based)
Daily
Influenza Associated Pediatric
Mortality
Daily
EIP Influenza Surveillance Network
Weekly
New Vaccine Surveillance Network
Weekly
State and Territorial Epidemiologists
Report
Daily
Sentinel Provider Surveillance
Network (subset)
Daily
Aggregate Case Reporting
NR
C
A
D
E
F
G
B
Interval D
Acceleration
Interval D
Triggers
Multiple laboratory confirmed cases
in a state without epi-link
Federal Actions
Maintain surveillance
Conduct lab confirmation and
characterize viruses (targeted)
Studies of clinical course
Evaluate case fatality ratio and PSI
Reporting
Frequency
WHO & NREVSS Collaborating
Laboratories (subset)
Daily
Novel Influenza A Virus Infections
Daily-NR
122 Cities Mortality Reporting
System (web-based)
Daily
Influenza Associated Pediatric
Mortality
Daily
EIP Influenza Surveillance Network
Weekly
New Vaccine Surveillance Network
Weekly
State and Territorial Epidemiologists
Report
Daily
Sentinel Provider Surveillance
Network (subset)
Daily
Aggregate Case Reporting
Daily
C
A
D
E
F
G
B
Interval E
Peak Transmission
Interval E
Triggers
>10% specimens submitted from
states + for pandemic strain
Federal Actions
Continue virologic characterization
Maintain surveillance
Transition to surveillance for
mortality and syndromic disease
Reporting
Frequency
WHO & NREVSS Collaborating
Laboratories (subset)
Daily
Novel Influenza A Virus Infections
NR
122 Cities Mortality Reporting
System (web-based)
Daily
Influenza Associated Pediatric
Mortality
Daily
EIP Influenza Surveillance Network
Weekly
New Vaccine Surveillance Network
Weekly
State and Territorial Epidemiologists
Report
Daily
Sentinel Provider Surveillance
Network (subset)
Daily
Aggregate Case Reporting
DailyWeekly
C
A
D
E
F
G
B
Interval F
Deceleration
Interval F
Triggers
<10% specimens submitted from
states + for pandemic strain
Federal Actions
Continue virologic characterization
Maintain surveillance for
mortality and syndromic disease
Reporting
Frequency
WHO & NREVSS Collaborating
Laboratories (subset)
Daily
Novel Influenza A Virus Infections
NR
122 Cities Mortality Reporting
System (web-based)
Daily
Influenza Associated Pediatric
Mortality
Daily
EIP Influenza Surveillance Network
Weekly
New Vaccine Surveillance Network
Weekly
State and Territorial Epidemiologists
Report
Daily
Sentinel Provider Surveillance
Network (subset)
Daily
Aggregate Case Reporting
DailyWeekly
C
A
D
E
F
G
B
Interval G
Resolution
Interval G
Triggers
<1% specimens submitted from
states + for pandemic strain during
a two-week period
Federal Actions
Return to routine virologic testing
Maintain surveillance for
mortality and syndromic disease
Reporting
Frequency
WHO & NREVSS Collaborating
Laboratories (subset)
Weekly
Novel Influenza A Virus Infections
NR
122 Cities Mortality Reporting
System (web-based)
Weekly
Influenza Associated Pediatric
Mortality
Daily
EIP Influenza Surveillance Network
Weekly
New Vaccine Surveillance Network
Weekly
State and Territorial Epidemiologists
Report
Weekly
Sentinel Provider Surveillance
Network (subset)
Weekly
Aggregate Case Reporting
Weekly-NR
Pandemic Surveillance
C
Initiation
A
Investigation
D
Acceleration
B
Recognition
Rapid spread within a jurisdiction
Multiple lab-confirmed cases w/o an epi link
?
E
Peak
Transmission
F
Deceleration
G
Resolution
Surveillance Realities
• Few hospitalizations and deaths
– Rethink our strategy
• Mild to moderate clinical illness
• Age distribution of cases and persons hospitalized similar to that of
seasonal H1N1
Surveillance Realities
• Needed to re-focus surveillance
– ILINet has been our lifeline to influenza activity
– Aggregate reports and line listed data
• Limited by testing practices
– Need for information about burden of illness and clinical spectrum
• Community Household Surveys
– Need for information about what states are doing and can do
• Rapid Survey of Surveillance Activities in states
• ILINet, other systems, lab and testing
Surveillance Planning
• Dynamic situation
– Information requirement modulated by
• pandemic interval
• severity of illness
• planning public health interventions (vaccine, hospital surge,
stockpile)
• hypothesized “mixed” season with 5 viruses circulating
• hypothesized increase in transmissibility of the virus
Surveillance Planning
• Summer
– Option 1 Current Strategy
• Weekly aggregate reporting
• ILINet (subset)
• Automated syndromic systems
• WHO/NREVSS daily (subset)
– Option 2 Scale back
• D/C weekly aggregate reporting (states post case counts?)
• ILINet Weekly
• WHO/NREVSS weekly
Surveillance Planning
• Fall
– Option 1 Continue Current Summer Strategy
• Weekly aggregate reporting
• ILINet daily (subset)
• Automated syndromic systems (BioSense, etc)
• WHO/NREVSS daily (subset)
– Option 2 Scale Up
• Return to daily line listed case reporting or web based CRF
– Staggered reporting of CRF
• Hospitalization case reporting (long or shorter form)
– First “200” or EIP if widespread
• Other systems daily
Next steps
• Convene CSTE working group comprised of state
Epidemiologists and surveillance coordinators
Additional Information
• CDC/Influenza Division FluView surveillance
report
– Weekly from October through mid-May
– http://www.cdc.gov/flu/weekly/fluactivity.htm
• General influenza information
– http://www.cdc.gov/flu/
• Avian influenza information
– http://www.cdc.gov/flu/avian/
• Pandemic influenza
– http://www.pandemicflu.gov/
Influenza Surveillance Regions
Pacific - 9
Mountain - 8
West North
Central - 4
East North
Central - 3
Mid
Atlantic - 2
New England - 1
South Atlantic - 5
East South
Central - 6
Pacific - 9
West South
Central - 7
Number of Specimens Tested for Influenza and Number
Positive
Season
All labs
# tested
# positive
2002-03
96,871
9,841
2003-04
152,262
25,104
2004-05
186,478
24,501
2005-06
180,961
21,497
2006-07
189,415
23,941
2007-08 *
235,436
40,167
*data as of July 18, 2008
National Center for Health Statistics Mortality Data
• Provides a complete and more detailed record of cause
of death
• > 99% of all deaths in the US
• Separate record for each individual
– Basic demographic data
– Date of death
– Underlying & contributing causes of deaths
• Data used for special studies
– Mortality estimates obtained from mathematical modeling
• Not available until ~ 2 yrs later
Growth of the Influenza Sentinel Physician
Surveillance System
3000
20000000
18000000
16000000
14000000
2000
12000000
1500
10000000
8000000
1000
6000000
4000000
500
2000000
0
0
1996-97 1997-98 1998-99 1999- 2000-01 2001-02 2002-03 2003-04 2004-05 2005-06 2006-07 2007-08*
2000
Season
enrolled physicians
* As of 7/18/2008
regularly reporting physicians
patient visits
Patient visits
Enrolled Physicians
2500
1997-40
1997-50
1998-07
1998-17
1998-46
1999-04
1999-14
1999-43
2000-01
2000-11
2000-40
2000-50
2001-08
2001-18
2001-47
2002-05
2002-15
2002-44
2003-02
2003-12
2003-41
2003-51
2004-09
2004-19
2004-48
2005-06
2005-16
2005-45
2006-03
2006-13
2006-41
2006-51
2007-09
2007-19
2007-47
2008-05
2008-15
% of Visits for ILI
Percentage of Visits for ILI Reported by Sentinel Providers,
National Summary, 1997-98 – 2007-08
8
7
6
5
4
3
2
1
97-98
98-99
99-00
00-01
01-02
02-03
Week
03-04
04-05
05-06
06-07
07-08
0
Influenza Activity Levels
• No Activity: No laboratory-confirmed cases of influenza and no
reported increase in the number of cases of ILI
• Sporadic: Small numbers of laboratory-confirmed influenza cases
or a single influenza outbreak has been reported, but there is no
increase in cases of ILI
• Local: Outbreaks of influenza or increases in ILI cases and recent
laboratory-confirmed influenza in a single region of the state
• Regional: Outbreaks of influenza or increases in ILI and recent
laboratory confirmed influenza in at least 2 but less than half the
regions of the state
• Widespread: Outbreaks of influenza or increases in ILI cases and
recent laboratory-confirmed influenza in at least half the regions of
the state
.
.
.
.
.
Current Status of WHO System
• >175,000 isolates/yr (600 to 1200 M cases)
• WHO CCs receive 6,500 – 8,000 samples/yr.
• WHO CCs and NICs sequence HA of 1,000
samples/yr; complete genomes now
sequenced (e.g, members of GIP sequenced
complete genomes of 20 H5N1 viruses in few
weeks)
• >290 M doses of influenza vaccine w/wide
2007-08 Surveillance Summaries
U.S. WHO/NREVSS Collaborating
Laboratories National Summary, 2007-08
5000
50
A(H3)
4500
A(H1)
A(Unsubtyped)
40
B
Percent Positive
Number of Isolates
3500
3000
30
2500
2000
20
1500
1000
10
500
0
0
40
42
44
46
48
50
52
2
4
Week
6
8
10
12
14
16
18
20
Percent Positive
4000