population movement, quarantine and isolation: pieces of the pandemic influenza puzzle peter houck,...

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

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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

0

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0 1 2 3 4 5-6 7-8 >8Time from onset to isolation (days)

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Secondary

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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?