7. Disease Outbreak 2013

8/11/2019 7. Disease Outbreak 2013

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DISEASE

DEPARTMENT OF EPIDEMI

2

OUTBREAK

OLOGY AND BIOSTATISTICS

013

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OUTBREAK

EPIDEMIC

ENDEMIC

PANDEMIC

SEASONAL VAR

CHANCE

ATION

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EPIDEMIC/OU

The occurrence of cases of

related behavior, or other h

a community or region,c ear y n excess o norma

The community or region and theare specified precisely.

BREAK

n illness, specific health-

alth-related events, in

xpec a ons.

eriod in which the cases occur

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EPIDE

The number of cases in

of an epidemic varies a

the a ent

size and type of po

previous experienc

lack of exposure to

time and place of o

IC

dicating the presence

cording to :

ulation exposed

the disease

currence.

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ENDE

The constant presence of

or infectious a ent within

area or population group;

usual prevalence of a give

area or group

IC

a disease

iven eo ra hic

ay also refer to the

n disease within such

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PANDEMIC

Worldwide epidemic

SEASONAL VARIAT

Change in physiologic

or in disease occurren

regular seasonal patt

ION

al status

ce that conforms to a

rn

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CHAN

A set of cases that occur

BUT

do not surpass the expec

region

E

in a short period of time

ed numberof cases for the

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Infectious

(Communicable

An illness due to specific i

that agent or its products f

animal or reservoir to a su

isease

Disease)

fectious agent

rom an infectious person,

sceptible host.

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Factors Involved

Agen

Agent, host and environ

and are interdependent in th

Environment

in Infection

ent interrelate

e production of disease

Host

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Types of Tra

Direct transmission (pers Direct projection of dr

(sneezes and coughs :

Vertical transmission

(transplacental, from mot

Mucosa to mucosa

(sexually transmitted dis

Blood and transplants

(hepatitis)

Skin to skin

(staphylococcus)

nsmission

on to person) plet spray

easles)

her to child : HIV)

ase)

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Types of Tra

Indirect transmission

Vehicle-borne tra

(water, food, milk, bi

contaminated materi

Vector-borne tran

(mechanical, biologi

Airborne transmis

(microbial aerosols)

nsmission

smission

logical products,

als or objects)

mission

al)

ion

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Infectious Ch

Susceptible host

Agen

Mode of t

Portal of entry

in Model

Reservoir

t

ansmission

Portal of exit

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Other Defi

VehicleMode of transport of an infe

environment to a susceptibl

Vector

A living carrier(usually an a

mode of transport for an inf

host to a susceptible host.

Reservoir

The primary habitat in whic

and reproduces.

nitions

tious agent through the

host.

rthropod) that serves as a

ctious agent from an infected

an infectious agent survives

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Carrier

A person or animal that harbor

in the absence of discernable cl

as a potential source ofinfectio

Asymptomatic carrierSubclinical infection throu hou

Incubationary carrierInfectious carrier state occurs

preceding clinically recognizab

Convalescent carrierInfectious carrier state continu

clinically recognizable disease

a specific infectious agent

inical disease and serves

.

the infectious carrier state

uring the incubation period

le disease

s during convalescence when

is no longer present 14


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Perio

Exposure period

Time during which an indi

a source of infection

ncu a on per o

Time from initial infection (

clinical illness.

Latent period

Time from receiving infecti

s

idual or group is exposed to

entry of infection) to onset of

on to onset of infectiousness.

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Exposure period

Latent period

n ry o n ec on nse

Incubation per

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o n ec on nse o c n ca ness

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Perio

Infectious (or communicaPeriod during which an inf

to transmit the infectious a

Ser a nterva or genera

Interval between the same

in sucessive cases in a ch

Only applicable when infection

e.g. the interval between onset

onset of rash in a secondary c

s

ble) period cted person is able

ent.

on t me

stage of illness

in of transmission.

preads from person to person

of rash in the primary case to

se17


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Use of P

Useful for: Quarantine

Contact tracing Identification of possib

Outbreak investigation

Disease modeling and

riods

le time of infection

forecasting

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Types of O

1. Common sourceTransmission of an infectious

that is common to all outbrea

Point source : brief com

A single source of pathogen r

Extended source :

Common source exposure pr

- intermitten : at several point

- continuous : over a continuo

Onset will still be abrupt but c

a greater period of time than

depending upon how long the

tbreak

agent involving a source

-associated cases

on exposure.

esults in exposure of persons

sent over days or weeks

in time

us period

ases would be spread over

ne incubation period

exposure persists. 19


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Types of O

2. Propagated or progressi

- Caused by the spread of thefrom one susceptible perso

- The curve tend to have a se

3. Mixed epidemic

Involves both a common sourcpropagated spread to other ind

Many foodborne pathogens co

of spread (hepatitis A, Shigella,

tbreak

e (person to person)

pathogen

to another.

ies of irregular peaks .

epidemic and secondary ividuals.

monly exhibit this mode

E.coli).20


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Elements of

Removal or elimination

pathogen

Blockage of the transm

m na on o suscep

(e.g. vaccination)

Control

of the source of the

ission process y

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DISEASE OUTBREAK

Data sources

The public

The media

Surveillance data

(laboratory reports, dise

NVESTIGATION

se notifications)

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When reports of an outbre

the following information s

e person s report ng t

Characteristics of the sus

(clinical information, susp

Persons directly affected

(epidemiological informati

ak are received,

hould be gathered :

e out rea

ected outbreak

cted etiologies)

y the outbreak

n)

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Steps in outbreak i

Establishing the existence o

Verifying the diagnosis

Defining and counting cases

Determining the population escr ng e ep em o ogy

Developing hypotheses

Evaluating the hypotheses

Undertaking additional epideand laboratory studies, as n

Implementing control and pr

Communicating findings

nvestigation

an outbreak

t risk

miological, environmental cessary

vention measures

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CONFIRMATION & VERDIAGNOSIS

Check the report whether it is

Verify the sign or symptoms a

To proof the case is based on

the sign or symptoms

Estimate the number of case

If there is sufficient of time, a

should be done to make an e

FICATION OF

true or not

nd the diagnosis

the history of the disease and

laboratory examination

iological diagnosis

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DETERMINE THE EVENT :

IS IT AN EPIDEMIC O

How much the usual morb

Based on time, place, per

How are the usual pattern

Is there an increase of the

Is it conspicuous or not?

Make a graph ofepidemic

of the sign in each case!

NOT?

idity rate are?

on

of the disease in the community?

number of cases?

curve based on time of onset

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DESCRIBE THE EPID

TIME, PLACE, PER

TIME

When was the first case fo

How long the epidemic/out

Find the probable of the fir

Assume the type of the epi

(common source? person t

MIC :

ON

nded? The last?

break happened?

t exposed time!

demic!

o person?)

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PLACE What place is the most pro

What are the attack rate ba

PERSON

Identify the age specific an

What group has the highes Determine that the charact

significantly compared with

inent number of cases?

ed on places?

sex specific attack rate!

and the lowest attack rate? ristic of the cases are differ

the whole population

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COLLECTING DATA

To get the real data.

Can be simultaneously wit

verification :

- a are e exac num

- Who are the population

- Who are the contact per

- Think about loss of obse

- Who are the carrier ?

Those data could be obtain

the activity of diagnosis

er o cases

t risk ?

on ?

rvation !

ed by house to house visits !29


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IDENTIFICATION OF AGOF INFECTION AND T

First we have to set hypothesis

The etiological agent

The source of infection

The exposure time

The incubation period

The transmission of infectio

The population at risk

ENT OR THE SOURCE ANSMISSION

of :

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EPIDEMIC CONTROL

1. THE PATIENT

Adequate and prompt tr

2. CONTROLLING against :

The primary source of in

The reservoir (carrier, v

Transmission vehicle (fo

Susceptible contact per

3. EPIDEMIOLOGICAL SU

MANAGEMENT)

eatment

fection

ctor, environment)

od, fluid, air etc.)

on

VEILLANCE31


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INVESTIGATI

The main objection of the

of epidemic, to organize and o

and to improve the previous p

N REPORT

report :

perate a surveillance activity

evention and controlling activity.

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INVESTIGATI

The form of the report :

1. INTRODUCTION

It content description of th

2. BACKGROUNDA brief description about f

(e.g. geographic, politic, e

historic)

N REPORT

e condition that stimulate to

ctors that cause the problem

conomic, demographic and

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3. DESCRIPTION OF INVARRANGEMENT

Include :

- the reason

- the method

- source of information

- how to explore the cases

- verification of diagnoses

- use of sample cases and

STIGATION

control in analyzing data,etc.

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4. THE FINDINGS

Only the fact finding should b

discussion or suggestion. Th

the previous data as it happe

The findings will be presente

- characteristic table of age,

their attack rate- the onset of illness with the

- the result of laboratory test

- other evidence which might

of infection or suspected

e reported; without any comment,

recent data could be related to

ned as an epidemic.

in tables or graph such as :

ex, race, occupation etc. and

graph

direct the possibility of the source

source. 35


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ANALYZING DATA A

Data should be interpreted t

- agent of infection

- source of infection

- reservo r

- disease transmission, includi

- the high risk group populatio

It is exactly useful if the cha

epidemic compared with the

D CONCLUSION

o construct hypothesis of :

ng the vehicle or vector

acteristic of the recent

similar epidemic before.

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DESCRIBE THE CO

Clarify the objective of the acti

Discuss each of this action ba, ,

Describe the results and the e

Explain that there might be p

cases after passing one incubcontrol action.

TROL ACTION

on specifically

ed on :

penses of the actions.

ssibility of explosion of new

tion period after the

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DESCRIBE THE

a. The consequences of theand economic status

b. The consequences of the cPopulation immu

Reservoir numb

Vector numb

c. The invention of new infec

transmission of agent etc.

UTCOMES

pidemic to health condition

ontrol action to :ity status, way of life, etc.

r and distribution

r,density, distribution

ious agent, reservoir,

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RECOMMEN

The objection is to improve

control.

activity, what data should b

of data, how to consolidate

dissemination of the report,

epidemic, what kind of coo

ATION

the surveillance activity and

collected, what is the source

after an epidemic,

who will be responsible in an

eration should be organized.

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EPIDEMIC

A graph of cases of diseas

or hour) of onset of illness

Mainly used in outbreak in

CURVE

plotted against time (date

estigation

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EPIDEMIC

8

9

10

Point source epidemic

0

1

2

3

4

5

6

7

01/0

1/1900

03/0

1/1900

05/0

1/1900

07/0

1/1900

09/0

1/1900

11/0

1/1900

13/0

1/1900

15/0

1

Date of

NumberofCases

CURVE

1900

17/0

1/1900

19/0

1/1900

21/0

1/1900

23/0

1/1900

25/0

1/1900

27/0

1/1900

29/0

1/1900

Onset of Illness

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Cases of Salmonello

25

30

Extended source epidemic

0

5

10

15

20

4a

4p

5a

5p

6a

6p

7a

7p

8a

8p

9a

Onset by

N

umberofcases

sis by Date of Onset

9p

10a

10p

11a

11p

12a

12p

13a

13p

14a

14p

15a

15p

12 hour intervals

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ATTACK

Similar as inci

n

Incidence Rate =

It is used in a short period of

the population being affecte

the duration of epidemic is s

P

ATE

ence rate :

w events / cases

x k

an event - an outbreak -,

is limited closely,

ort period.

opulation at risk

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Definitions in an outb

CLINICAL DESCRIPTION

Sign and symptoms found in

CASE DEFINITION Standard set of criteria for de

should be classified as havin

A case definition includes clisetting of an outbreak invest

and person.

reak investigation

the outbreak

ciding whether an individual

the health condition of interest.

ical criteria and particularly in the igation restrictions by time, place,

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Case defi

Confirmed cases

- have a positive laboratory r

- high spesificity

have the typical clinical featu

laboratory confirmation

Possible cases

- have fewer or atypical clinic

- high sensitivity

ition

sult

es of the illness, but without

al features

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DIFFERENTIAL DIA

List of possible diagnosis

possible one

DESCRIPTIVE EPIDE

Characterize the outbrea

NOSIS

, ordered from the most

IOLOGY

by time, place and person

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PlaceA. The occurrence of diarrhea b

community A and B in Janua

Source of water

supply

Sick Not Sick

Community A 98 57

Community B :

Not exposed by water

supply A

9 132

Visit A :

1. Drank water of A

2. Not drank water of A

22

0

18

6

Total Community B 31 156

The attack rate of B was much lower than

In other case, people of B who visited A a

the attack rate was 55.0% ;a quite high in

Conclusion : water supply A was respon

source of water supply of ry 2011

total Attack Rate

155 63.2 %

141 6.4 %

40

6

55,0 %

0

187 16.6 %

the attack rate of A.

nd drank the water A became sick,

cidence.

ible for the occurrence of diarrhea. 51


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Rank of Class No. of Cases No. of s

Test Class

1

2

3

4

5

24

17

7

8

4

23

8

8

6

9

10

9

B. Attack rate by class in Ganado P

6

Special Class

12

5

9

1

Total 100 6

The table shows that the highest ri

population, followed by the test cla

The lowest is the 4th class.

tudent Attack Rate in %

5

6

1

0

4

9

28.2

19.8

11.5

8.9

3.8

23.2

ublic School, Arizona in March 2011

5

2

12.6

41.7

2 15.8

k is the special class out of the whole

s, the 5th and the first class.

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C. The occurrence of hepatitis A

who work at night at May

Work

nightly

Sick Not sick

Yes 10 12

No 2 26

Total 12 38

The table shows that the night wor

hepatitis than non night worker.

among restaurant worker

12 and 13, 2011

Total Attack

rate

22 45 %

28 7 %

50 24 %

ers are much higher risk to get

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PERSON

Attack rate per 100 person b

in Polyclinic A.

Age group

in year

Examined

regularly

Di

1

2

20

19

Group of 1 & 2 years are the high

followed by group of 3 years.

4

5

6+

39

38

18

Total 173

age group in diarrhea

arrheal

Cases

Attack Rate

(%)

17

15

85

79

st risk of getting diarrhea,

4

5

1

10

13

6

55 32

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An OCT may be considered w The outbreak poses an imme

local population

There are many cases

The disease is important in tepropensity to spread

Cases have occured over a wi

obvious point source

Cases have occured in high-ri(schools, day-care centres, ho

premises,etc.)

en : iate health hazard to the

ms of its severity or its

despread area without

k establishments spitals, food

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The role of the OCT :to coordinate all the activiti

investigation and control of

This may involve :1. Deciding whether there is r

2. Deciding on the type of inv

conducted

3. Case-finding and interview

4. Planning the appropriate cli

sampling

s involved in the

an outbreak.

ally an outbreak

stigations to be

nical and environmental

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5. Ensuring that all collabor

methodology

6. Conducting an environm

7. Agreeing and implementi

prevent the further sprea

8. Working in concert with l

make recommendations

prophylaxis

tors use a complementary

ntal investigation of

g control measures to

cal medical providers to

n treatment and/or

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9. Organizing ongoing com

members about the outb

.

11. Producing reports, includ

health authorities and ot

12. Requesting external assi

(e.g. secondment of a na

munications among OCT

eak

ing lessons learned, for

er interested parties

tance

tional investigation team)

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7. Disease Outbreak 2013

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