population movement, quarantine and isolation: pieces of the pandemic influenza puzzle peter houck,...
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Population Movement, Quarantine and Isolation: Pieces of the Pandemic
Influenza PuzzlePeter Houck, M.D.
Medical Officer, Seattle Quarantine StationDivision of Global Migration and Quarantine
National Center for Infectious DiseasesCenters for Disease Control and Prevention
August 24, 2006
Population MovementMain 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
SAFER • HEALTHIER • PEOPLE
22
4 x increase in volume as compared to 1960-754 x increase in volume as compared to 1960-75Source: Population Action International 1994
Major Migration Flows: 1990s
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
SAFER • HEALTHIER • PEOPLE
A Shrinking WorldA Shrinking World
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SAFER • HEALTHIER • PEOPLE
Wor
ld P
opul
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Speed of Global Travel in Relation toWorld Population Growth
From: Murphy and Nathanson. Semin. Virol. 5, 87, 1994
SAFER • HEALTHIER • PEOPLE
International Tourist Arrivals - International Tourist Arrivals -
WorldWorld
0100200300400500600700800900
1000
1970 1980 1990 2000 2010
Year
Tou
rist
Arr
ival
s (m
illi
ons)
Estimated Annual International Arrivals , U.S.A.
International Travelers Foreign 60 M / U.S. 60 M
Immigrants1,000,000
Refugees70-90,000
U.S.-Mexico Border Crossings 400M?
SAFER • HEALTHIER • PEOPLE
Seattle and Narita AirportsSeattle and Narita Airports
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
Los Angeles 22%Los Angeles 22%
San Francisco 15%San Francisco 15%
Guam 11%Guam 11%
Honolulu 15%Honolulu 15%
New York: 8%New York: 8%Chicago 6%Chicago 6%Detroit 5%Detroit 5%
1 Includes Brunei, Cambodia, China/Hong Kong, Indonesia,Japan, Laos, Malaysia, Myanmar, Philippines, Singapore,South Korea, Taiwan, Thailand, Vietnam, Japan
Proportion of 2.79 million passengers directly arriving from East Asia, by airport Jan – Mar 2005
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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 AngierNew 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 SpreadIra Longini et al, 2006
The Basic SIR Model of Infectious Disease
Contact tracingPublic health
notified2º case
ascertainment
Period of communicability
Contagion Epidemic ModelingGoal: R< 1, Extinction or Quenching
d(sx)d(exp) d(hc) d(ddx) d(ic end)d(ic onset)
Infection Exposure
Symptom onset
Pt seeks health care
Influenza diagnosis
Appropriate infection control isolation, treatment
Encounter Recognition Isolation initiated
Isolation ended
Pre-symptomatic spread?
Incubation1-4 days
Period of risk for epidemic propagation
Time (days)# 2º contacts exposed and infected
Duration of isolation
Time (days)
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
Suppression
Ro = 0.67,
Progression = 1:2:4:3:2
Exponentiation
Ro = 2.0,
Progression = 1:2:4:8:16
Effect of Increasing Social Distance (Q&I) on Epidemic Dynamics
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
• 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
Definitions
What is the Evidence?
• Real life experience• SARS
• 1918 pandemic
• Mathematical models
Example: SARS 2003
Atlanta Journal-Constitution 3/18/03
SARS Containment Strategy
IsolationSurveillance/ Monitoring
Quarantine
Early Detection
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 1,449 (0.2%) 10 (0.001%)
Train stations 5,246,100 2,575 (0.05%) 2(<0.001%)
Roads 7,365,600 577 (0.008%) 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
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0 1 2 3 4 5-6 7-8 >8Time from onset to isolation (days)
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Close contacts: SARS Attack rates, Beijing 2003
Zonghan Zhu, M.D., Beijing Municipal Health Bureau, IEIDC Quarantine Conf 2004
Relationship Attack Rate %
Spouse 15.4
Non-household relative 11.6
Friend 10.0
Household member 8.8
Unknown 4.5
Work/school contact 0.4
Healthcare worker 0.0
Other 0.0
Total 6.5
Efficiency of Quarantine: SARS 2003
SARS attack rate among those quarantined
• Hong Kong (n=1,262)– Household contacts 2.7%
• Taiwan (n= 131,132)– Overall 0.09%– Close contact 0.22%– Travel 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 infectionDay 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)
Source: Harvard School of Public Health/Health Canada, June 2003
Percent experiencing problems while quarantined
11%
26%
51%
10%
11%
24%
Major ProblemMinor Problem
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
Emotional difficulties being confined
Not getting paid because they missed work
Specific Problems
*Robert Blendon, Harvard School of Public Health
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?