SARS Epidemiology for Public Health Action

Aileen J Plant

on behalf of

The Global Network for SARS EpidemiologyWith thanks to Angela Merianos, Angus Nicoll and all the

SARS epidemiology people around the globe!

SARS

A triumph for networks!

Today

Brief description of epidemiology(Who? When? Where? Why? How?)

Epidemiology for public health action

Highlight the unknown

The challenges ahead

The initial challenge

No name No clear-cut clinical diagnosisNo testNo idea of clinical courseNo idea of long term implicationsNot much idea how it spreadWhen does infectiousness start?When does infectiousness finish?Is there any short term immunity?Is there any long term immunity?

Notifications of SARS to WHO by week (21 March-13 June, 2003)

0

200

400

600

800

1000

1200

1400

1600

21-M

ar

28-M

ar

4-Ap

r

11-A

pr

18-A

pr

25-A

pr

2-M

ay

9-M

ay

16-M

ay

23-M

ay

30-M

ay

6-Ju

n

13-J

un

Source: www.who.int

• Incubation period• Infectious period• Case fatality ratios• Reproduction number• Routes of transmission and exposure dose• Sub-clinical infection• Reservoirs eg animals

Incubation period – imprecise but reasonably consistent

0

2

4

6

8

10

12

14

16

18

Minimum Mean Maximum

CanadaChinaHong Kong SARSingaporeVietnamWHO Europe

Transmission evidence

Asymptomatic Mild symptoms

Sick

Infectiousness

?

Recovering

?

X Y YYY XQuality of evidence

Case fatality ratios – crude estimates

0

5

10

15

20

11-A

pr

18-A

pr

25-A

pr

2-M

ay

9-M

ay

16-M

ay

23-M

ay

30-M

ay

6-Ju

n

13-J

un

Perc

enta

ge

Vietnam Hong Kong SingaporeCanada China Taiwan Province

Routes of tranmission

All the evidence in favour of close contact • Mostly <1 metre• Fomites can not be excluded – BUT –not much evidence of prolonged risk in spite of microbiological findings• Aerosol is not likely• Amoy Gardens ???

Cumulative percentage of SARS cases by country and time

0

20

40

60

80

100

28-F

eb

7-M

ar

14-M

ar

21-M

ar

28-M

ar

4-Ap

r

11-A

pr

18-A

pr

25-A

pr

2-M

ay

9-M

ay

16-M

ay

23-M

ay

30-M

ay

6-Ju

n

13-J

un

Perc

enta

ge

VietnamHong KongSingaporeCanadaChinaTaiwan Province

Health Care Workers and SARS

HCWHong Kong SAR 58%

(early report – Lee et al)

Vietnam 53%

Sick health care workers matter for SARS but they matter far more for the rest of the health system

SARS Vietnam: clinical attack rates by occupational risk groups

Hospital A %Any doctor 16Any nurse 35Administration staff 2Other staff with patient contact 53Outside staff 0Total hospital 18

Concurrent patients NOT 7admitted for SARS

Hospital B 0

Contacts of one well-tracked 6 (and friendly!) case

Conclusions – the challenges ahead

• clinical diagnostic skills• laboratory capacity• surveillance capacity• response capacity• plans of action• infection control• applied research capacity

MUST have sufficient:

Conclusions

There is a lot of epidemiological work to be done

But the good news is

We don’t have to wait for perfect answers to control SARS, we can

do it now!

Photo: Dr Joel Montgomery, WHO SARS Team, Vietnam

Mean age and SARS

Hong Kong SAR 39.3 (n = 156, Lee et al)

Hong Kong SAR 39.8 (n = 75, Peiris et al) (Amoy Gardens)

Vietnam 40.8 (n = 62, unpub)

SARS Vietnam: Feb-Mar 2003No of cases by date of onset – the incubation period

0

1

2

3

4

5

6

7

8

9

10

Feb

22

Feb

24

Feb

26

Feb

28

Mar

2

Mar

4

Mar

6

Mar

8

Mar

10

Mar

12

Mar

14

Mar

16

Mar

18

Mar

20

Mar

22

Mar

24

Mar

26

Mar

28

Mar

30

Apr 1

Apr 3

Apr 5

Apr 7

No

of c

ases

Index case admitted

Maximum-minimum incubation period(5 days)

Median IP (6-7 days)

Max IP (10 days)

Infection control - it matters!

0

2

4

6

8

10

Feb

22

Feb

24

Feb

26

Feb

28

Mar

2

Mar

4

Mar

6

Mar

8

Mar

10

Mar

12

Mar

14

Mar

16

Mar

18

Mar

20

Mar

22

Mar

24

Mar

26

Mar

28

Mar

30

Apr 1

Apr 3

Apr 5

Apr 7

Num

ber o

f cas

es

HCW Other

Infection control strengthened

Floor of hospital isolated

No of cases by date of onset of symptoms, Vietnam

Maximum incubation period