Epidemiology and Surveillance: Lessons from

Past Pandemics

Arnold S. Monto, MDProfessor of Epidemiology

University of Michigan School of Public HealthFounding Director

University of Michigan Bioterrorism Preparedness InitiativeAnn Arbor, MI

Basic Questions

• When will the virus arrive and spread? How long from the source?

• What will the principal age and other risk groups be?

• How many will be affected?– Morbidity?

– Mortality?

Source of Pandemic Viruses

Pandemic Years

Influenza A Subtype Viral Change

1918-19191918-1919 H1N1 Mutation from Avian Virus2 kinds identified

1957-19581957-1958 H2N2 Reassortment3 segments from Avian Virus

1968-19691968-1969 H3N2 Reassortment2 segments from Avian Virus

Effects of Past Pandemics on the US

Source: NVPO.

Pandemic Years

Estimated US Deaths

Influenza A Subtype

Populations at Greatest Risk

1918-19191918-1919 500,000 H1N1 Young; healthy adults

1957-19581957-1958 70,000 H2N2 Infants; elderly

1968-19691968-1969 34,000 H3N2 Infants; elderly

The 1918 Pandemic in Asia and Africa: Influenza-Associated Deaths

• Asia– India: 12.5 million deaths (higher than bubonic

plague)

– Japan: 257,000 deaths

– Rest of Asia: 3,000,000 deaths

• Africa– Union of South Africa: 139,471 deaths out of

6,100,000 population

– Madagascar: 114,000 deaths out of 3,250,000 population

Jordan, ED. Epidemic Influenza, AMA. Chicago, 1927.

Review of Past Pandemics

• Age Specificity:Age Specificity:

• Traditional view:Traditional view: “U” or “J” shaped curves in most pandemics; “W” shaped curve in 1918.

• Variations:Variations: 1889-1890—Reports from UK of high mortality in young adults– Sparing of elderly in 1918– Relatively higher death rates in young

adults in more recent pandemics• Will past history predict the future?Will past history predict the future?

Pneumonia and Influenza Mortality in Influenza Pandemics

0

500

1000

1500

2000

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Age (Years)

Death

s p

er

100,0

00 P

opula

tion 1892 Massachusetts

1918 United States Registration Area

1957 United States

*Modified from Dauer & Serfling. Am Rev Resp Dis. 1961; 83:15-28.

Age-Specific Influenza Death Rates Among Females in England and Wales, 1918

Nguyen-Van-Tam, JS, et al. Vaccine. 2003;21:762-68.

1957

Influenza Attack Rates by Age in Tangipahoa Parish, Louisiana: August, 1957

0

10

20

30

40

50

60

70

0 4.5 7.5 12 20 30 40 55 77Age in Years

Cas

es P

er 1

00 P

erso

ns

Dillon School Families West Side School Families Independence School Families

Langmuir AD. Am Rev Resp Dis. 1961;83:5.

1968

Weekly Incidence of Influenza-like Diseasesin Hong Kong: June to September 1968

0

500

1000

1500

2000

2500

3000

3500

15 22 29 6 13 20 27 3 10 17 24 31 7 14 21 28

No.

of

Not

ifica

tions

June July Aug. Sept.

*Cockburn et al. Origin and progress of the 1968-69 Hong Kong Influenza epidemic. Bull. Wld Hlth Org. 1969;41:345-8.

Week Ending

Peak Influenza Activity in the US by State and Week: 1968-69

0

2

4

6

8

10

12

12 19 26 2 9 16 23 30 7 14 21 28 4 11 18 25 1 8

Sta

te

Oct. Nov. Dec. Jan. Feb.

*Sharrar RG. National Influenza Experience in the USA, 1968-69. Bull. Wld Hlth Org. 1969;41:361-6.

Week Beginning

Number of Episodes of Illness, Healthcare, Utilization, and Death Associated with Moderate

and Severe Pandemic Influenza Scenarios*

Characteristic Moderate(1958/68-Like)

Severe(1918-Like)

Illness 90 million (30%) 90 million (30%)

Outpatient Medical Care 45 million (50%) 45 million (50%)

Hospitalization 865,000 9,900,000

ICU Care 128,750 1,485,000

Mechanical Ventilation 64,875 742,500

Deaths 209,000 1,903,000

*Estimates based on extrapolation from past pandemics in the United States. Note that these estimates do not include the potential impact of interventions not available during the 20 th

century pandemics. Source: NVPO.

Conclusions

• The 1918 outbreak was unique in terms of numbers of persons involved and age groups affected. There is a question as to whether 1889-90 affected young adults disproportionately.

• It is difficult from historic records to document the presence or effect of the 1918 virus before the second wave. Once that wave began, it spread quickly.

• The 1957 virus probably spread for at least 6 weeks in China, starting in February, before emerging. It affected South America before spreading to North America in the early autumn.

• The spread of the 1968 virus was well documented from Hong Kong in July. The peak in the US was December-January.

• Numbers affected in the future will be based on multiple factors currently unknown, and any estimates must be viewed as provisional.