Population Movement,
Quarantine and Isolation:
Pieces of the Pandemic
Influenza Puzzle
Peter Houck, M.D.
Medical Officer, Seattle Quarantine Station
Division of Global Migration and Quarantine
National Center for Infectious Diseases
Centers for Disease Control and Prevention
August 24, 2006
Population Movement
Main Points
•
•
•
•
Permanent intercontinental migration increasing
Cross-border movement increasing
Speed and range of movement increasing
Any point on earth is within relatively few hours
of anywhere else
• Implications for spread and control of disease
Major Migration Flows: 1990s
4 x increase in volume as compared to 1960-75
Source: Population Action International 1994
SAFER • HEALTHIER • PEOPLE
2
Texas Land Ports of Entry*
• 12 bridges
• Incoming Cargo Trucks: 1,731,464
• Incoming Cargo Train Cars: 240,674
• Incoming Train Passengers: 8,365
• Incoming Vehicle Passengers: 96,894,839
• Incoming Bus Passengers: 1,942,990
• Incoming Pedestrians: 21,056,220
*USDOT, 2003
A Shrinking World
SAFER • HEALTHIER • PEOPLE
6
5
300
(
Days to Circumnavigate (
the Globe
350
)
400
4
250
200
3
150
2
100
50
1
0
0
1850
1900
Year
1950
From: Murphy and Nathanson. Semin. Virol. 5, 87, 1994
SAFER • HEALTHIER • PEOPLE
2000
World Population in billions
)
Speed of Global Travel in Relation to
World Population Growth
Tourist Arrivals (millions)
International Tourist Arrivals World
1000
900
800
700
600
500
400
300
200
100
0
1970
1980
1990
Year
SAFER • HEALTHIER • PEOPLE
2000
2010
Estimated Annual International Arrivals
, U.S.A.
Refugees
70-90,000
Immigrants
1,000,000
International Travelers
Foreign 60 M / U.S. 60 M
U.S.-Mexico Border Crossings 400M?
Seattle and Narita Airports
SAFER • HEALTHIER • PEOPLE
Narita International Airlines
Narita Roundtrips per Week: 2004
Boeing 777
Entry airports for 2.79 million directly-arriving
passengers from East Asia1, Jan - Mar 2005
Detroit 5%
San Francisco 15%
Chicago 6%
New York: 8%
Los Angeles 22%
1 Includes
Honolulu 15%
Guam 11%
Brunei, Cambodia, China/Hong Kong, Indonesia,
Japan, Laos, Malaysia, Myanmar, Philippines, Singapore,
South Korea, Taiwan, Thailand, Vietnam, Japan
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ago
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Guam
Hono
Fran
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Los A
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Percent
Proportion of 2.79 million passengers directly arriving
from East Asia, by airport Jan – Mar 2005
25
20
15
10
5
Airports of North America…Two Stops from
Anywhere
Slide from Don Burke, JHU MIDAS
“ Today, diseases as common as the cold and as
rare as Ebola are circling the globe with near
telephonic speed, making long-distance
connections and intercontinental infections as if
by satellite. You needn’t even bother to reach
out and touch someone. If you’re
homeothermic biomass, you will be reached and
touched.”
Natalie Angier
New York Times Magazine
6 May 2001
The Spread of Influenza
• Real life
• Virtual: Mathematical models
Person-to-Person Spread via Respiratory
Droplets, Aerosols, and Direct Contact
Influenza Pandemic, 1957
Global Spread, 2000-2001
• Viral strains often
originate in Asia
• Importance of
international air travel
• Implications for
pandemics
Findings When 2000 Air Travel Patterns
Added to 1968 Pandemic Model
• Disease progresses faster (180 vs. 320 days)
and farther
• Number of cases is greater with air travel
(188%)
• Less hemispheric seasonal swing
• Shorter time for effective intervention
• Suggests need for very effective
surveillance
Another Model of US Pandemic Spread
Ira Longini et al, 2006
The Basic SIR Model of Infectious
Disease
Contagion Epidemic Modeling
Goal: R< 1, Extinction or Quenching
Encounter
Incubation
1-4 days
Isolation
initiated
Recognition
Isolation
ended
Period of communicability
Period of risk for epidemic
propagation
Pre-symptomatic spread?
Duration of isolation
Time (days)
d(exp)
Infection
Exposure
d(sx)
Symptom
onset
d(hc)
Pt seeks
health care
d(ddx)
Influenza
diagnosis
Time (days)
d(ic onset)
d(ic end)
Appropriate
infection control
isolation,
treatment
# 2º contacts exposed and infected
Contact tracing
Public health
notified
2º case
ascertainment
The “Reproductive Number” R0
• “The average number of secondary cases
caused by an infectious individual in a
totally susceptible population”
• If R0 >1.0 the disease will spread
• If R0 <1.0 the disease will not spread
• R0 varies with disease, population, and
control measures
Effect of Increasing Social Distance
(Q&I) on Epidemic Dynamics
Exponentiation
Suppression
Ro = 2.0,
Ro = 0.67,
Progression = 1:2:4:8:16
Progression = 1:2:4:3:2
Ways to reduce R0 to <1.0 and control an
outbreak
• Reduce contact in population (increase
“social distance”)
• Reduce infectiousness of infected persons
through treatment, isolation, or quarantine
• Reduce susceptibility through vaccination
or antiviral medications
Definitions
• Isolation
– Separation of ill persons with contagious disease
– Often in a hospital setting
– Applied to individual level
• Quarantine
– Restriction of persons presumed exposed
– Applied at the individual or community level
• May be voluntary or mandatory
What is the Evidence?
• Real life experience
• SARS
• 1918 pandemic
• Mathematical models
Example: SARS 2003
Atlanta Journal-Constitution 3/18/03
SARS Containment Strategy
Early
Detection
Surveillance/
Monitoring
Quarantine
Isolation
Summary of surveillance for SARS at points of
transit as of June 30, 2003, Beijing
Transit site
Number of people
Number (%)
Number (%)
screened for fever
febrile
with SARS
--------------------------------------------------------------------------------------------------------------------Airport – international
275,600
496 (0.2%)
0 (0%)
Airport – domestic
952,200
Train stations
5,246,100
Roads
7,365,600
1,449 (0.2%)
2,575 (0.05%)
577 (0.008%)
10 (0.001%)
2(<0.001%)
0 (0%)
Zonghan Zhu, M.D., Beijing Municipal Health Bureau, IEIDC Quarantine Conf 2004
Isolation and Quarantine for
SARS 2003
Taiwan
– 671 cases isolated
– 131,132 persons quarantined
– Included 50,319 close contacts and 80,813 travelers
China
– 5,237 cases (2,521 in Beijing)
– 30,000 (approx) persons quarantined
Canada
– 250 cases (203 probable)
– 23,297 contacts identified
– Over 13,000 persons quarantined (Toronto)
Quarantine and surveillance of
close contact, Beijing SARS 2003
• 3565 public health workers were
mobilized to assist in the outbreak
investigation
• Close contacts were enforced in
quarantine for 14 days
• Home vs Centralized places
– 60% were quarantined at home
– 40% at centralized places such as
hotels and medical facilities
Zonghan Zhu, M.D., Beijing Municipal Health Bureau, IEIDC Quarantine Conf 2004
70
8
7
Primary
Secondary
S/P
6
50
Cases
5
40
4
30
3
20
2
10
1
0
0
0
1
2
3
4
5-6
7-8
Time from onset to isolation (days)
>8
Secondary cases/primary case
60
Close contacts:
SARS Attack rates, Beijing 2003
Relationship
Attack Rate %
Spouse
Non-household relative
Friend
Household member
15.4
11.6
10.0
8.8
Unknown
Work/school contact
Healthcare worker
4.5
0.4
0.0
Other
Total
0.0
6.5
Zonghan Zhu, M.D., Beijing Municipal Health Bureau, IEIDC Quarantine Conf 2004
Efficiency of Quarantine:
SARS 2003
SARS attack rate among those quarantined
• Hong Kong (n=1,262)
– Household contacts
• Taiwan (n= 131,132)
– Overall
– Close contact
– Travel
2.7%
0.09%
0.22%
0.09%
Quarantine Utility
What is the utility of “quarantine” for diseases
which are not infectious during the incubation
period?
To provide an observation window of several
days for evolution of symptoms, prompt and
prioritized clinical diagnosis and effective
isolation
Onset to Dx: 1.2 days vs. 2.9 days (p<0.006)
among those in Q compared those not in Q
(Taiwan 2003)
Quarantine at Entry?- Taiwan
• Incoming travelers (Level B) from affected areas
were quarantined
– 21 (0.03%) of 80,813 had suspect or probable SARS
– SARS was diagnosed in 0.36% of persons who sat
within 3 rows of a SARS patient on same airplane flight
• Close Contact (Level A) quarantine- 102/52,255
(0.20%) suspect or probable SARS
MMWR 2003;52:680-3
Quarantine and SARS
• Probably contributed much to SARS control
• Lots of people quarantined for each case detected
• Important differences between SARS and influenza:
1. incubation period (10 days vs. 1-4 days [??])
2. viral shedding when pre-symptomatic
3. SARS peak shedding during second week; flu
much earlier
• Differences make quarantine for flu very difficult
Quarantine in 1918 Pandemic
• Australia: 7-day Q + temperature monitoring of all ship
passengers thought to have delayed pandemic by about 3
months
• Madagascar: Quarantine delayed arrival by about 5-6
months
• American Samoa: quarantine prevented pandemic
• Africa, Canada, Australia: Attempts to quarantine at land
borders was not successful
Emerging Infectious Diseases 2006;12:81-87 or
www.cdc.gov/eid
When Is Quarantine Useful?
A Mathematical Model
Quarantine can have a substantial effect when:
• There is a large reproductive number (R0) when
only isolation is used
• A large proportion of infections from an ill
individual can be prevented by quarantine
• Asymptomatic individuals are likely to be
quarantined before developing symptoms
• Asymptomatic persons can transmit infection
Day et al. American J Epidemiology 2006
Assessing Collateral Damage
• What are the unintended consequences of
the interventions?
–
–
–
–
Adverse events
Economic (impact on traffic and trade)
Sociological (stigmatization, discrimination)
Psychological (depression, anxiety, PTSD)
Percent experiencing problems while
quarantined
BASE: Toronto area residents who had been quarantined or had a friend or
family member who had been quarantined (n=111)
In general, being
quarantined was a
problem
24%
51%
Specific Problems
Emotional
difficulties being
confined
Not getting paid
because they
missed work
11%
26%
10%
11%
*Robert Blendon, Harvard School of Public Health
Source: Harvard School of Public Health/Health Canada, June 2003
Major Problem
Minor Problem
Key Q-Questions
• What are the key trigger points for implementing
movement restrictions?
• What epidemic parameters are useful to monitor
impact?
• When is it safe to declare “all clear” & scale back
• Who will make the decision(s)?
• Who will implement?
• Will the measures be voluntary or enforced?
• Who will enforce, if needed?
• Who are all the partners/stakeholders and their roles?
• Are there sufficient resources for planning, education
and response?
More Basic Questions
•
•
•
•
•
•
•
How will the disease spread?
Who is at risk?
Is everyone on an airplane at risk?
Whom to quarantine?
Where to quarantine?
How long?
Who pays?