Outbreak investigation, response and control

IDSP training module for state and district surveillance officers

Module 8

Learning objectives (1/3)

• Define an outbreak/epidemic • List the various ways of detecting an

outbreak/ epidemic• List the modes of transmission of

causative agents of outbreaks• Describe warning signs of an impending

outbreak

Learning objectives (2/3)

• Specify the operational threshold levels of diseases under surveillance for outbreak investigations

• List the members of rapid response team in your district

• Enumerate the situations when DEIT would be initiated

• Describe the steps of epidemic investigation to establish an outbreak and determine its etiology

Learning objectives (3/3)

• Outline the appropriate control measures to be taken when the nature of the outbreak is established: Water borne diseases Vector borne diseases Vaccine preventable disease outbreaks Outbreaks of unknown etiology

Definition of an outbreak

• Occurrence in a community of cases of an illness clearly in excess of expected numbers

• The occurrence of two or more epidemiologically linked cases of a disease of outbreak potential constitutes an outbreak (e.g., Measles, Cholera, Dengue, Japanese

encephalitis, or plague)

Outbreak and epidemic: A question of scale

• Outbreaks Outbreaks are usually limited to a small area Outbreaks are usually within one district or few

blocks

• Epidemics An epidemic covers larger geographic areas Epidemics usually linked to control measures on a

district/state wide basis

• Use a word or the other according to whether you want to generate or deflect attention

Endemic versus epidemic

• Endemicity Disease occurring in a population regularly

at a usual level• Tuberculosis, Malaria

• Epidemics Unusual occurrence of the disease clearly in

excess of its normal expectation• In a geographical location• At a given point of time

Sources of information to detect outbreaks

• Rumour register To be kept in standardized format in each institution Rumours need to be investigated

• Community informants Private and public sector

• Media Important source of information, not to neglect

• Review of routine data Triggers

Early warning signals for an outbreak

• Clustering of cases or deaths• Increases in cases or deaths• Single case of disease of epidemic potential• Acute febrile illness of an unknown etiology• Two or more linked cases of meningitis, measles• Unusual isolate • Shifting in age distribution of cases • High vector density • Natural disasters

Objectives of an outbreak investigation

1. Verify 2. Recognize the

magnitude 3. Diagnose the agent4. Identify the source

and mode of transmission

5. Formulate prevention and control measures

Host

Environment Agent

An outbreak comes from a change in the way the host, the environment

and the agent interact: This interaction needs to be understood

to propose recommendations

Outbreak preparedness: A summary of preparatory action

• Formation of rapid response team• Training of the rapid response team• Regular review of the data • Identification of ‘outbreak seasons’ • Identification of‘outbreak regions’• Provision of necessary drugs and materials• Identification and strengthening appropriate

laboratories• Designation of vehicles for outbreak investigation • Establishment of communication channels in

working conditions (e.g., Telephone)

Basic responses to triggers

• There are triggers for each condition under surveillance

• Various trigger levels may lead to local or broader response

• Tables in the operation manual propose standardized actions to take following various triggers

• Investigations are needed in addition to standardized actions

Levels of response to different triggers

Trigger Significance Levels of response

1 Suspected /limited outbreak

• Local response by health worker and medical officer

2 Outbreak • Local and district response by district surveillance officer and rapid response team

3 Confirmed outbreak • Local, district and state

4 Wide spread epidemic • State level response

5 Disaster response • Local, district, state and centre

Importance of timely action: The first information report (Form C)

• Filled by the reporting unit• Submitted to the District Surveillance

Officer as soon as the suspected outbreak is verified

• Sent by the fastest route of information available Telephone Fax E-mail

The rapid response team

• Composition Epidemiologist, clinician and microbiologist Gathered on ad hoc basis when needed

• Role Confirm and investigate outbreaks

• Responsibility Assist in the investigation and response Primary responsibility rests with local health

staff

The balance between investigation and control while responding to an

outbreak

Source / transmission

Known Unknown

Etiology

Known Control +++Investigate +

Control +

Investigate +++

Unknown Control +++Investigate +++

Control +

Investigate +++

Steps in outbreak response

1. Verifying the outbreak2. Sending the rapid response team3. Monitoring the situation4. Declaring the outbreak over5. Reviewing the final report

Step 1: Verifying the outbreak

• Identify validity of source of information to avoid false alarm/a data entry error

• Check with the concerned medical officer:? Abnormal increase in the number of cases ? Clustering of cases ? Epidemiological link between cases ? Occurrence of some triggering event? Occurrence of deaths

Step 2: Sending the rapid response team

• Review if the source and mode of transmission are known

• If not, constitute team with: Medical officer Epidemiologist Laboratory specialist

• Formulation of hypothesis on basis of the description by time, place and person

? Does the hypothesis fits the fact YES: Propose control measures NO: Conduct special studies

Yes-> Control measures

Hypothesis fit the facts:-> Control measures

Hypothesis does not fit the facts:-> Further studies

Time, place person descriptionFormulation of hypothesis

No-> Clinical, microbiological

and epidemiological investigation

Yes-> Are the source andmodes of transmission

known?

No

Unusual event:Is this an outbreak?

Investigating an outbreak

Acute hepatitis by week of onset in 3 villages, Bhimtal block, Uttaranchal,

India, July 2005

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Week of onset

Num

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of c

ases

Outlying case-patient might have been a

source

Time

Incidence of acute hepatitis by source of water supply, Bhimtal

block, Uttaranchal, India, July 2005

Mehragaon main village

Dov

Water supplySpringReservoirPipeline

Attack rate< 5%5-9%10% +

Mehragaon Hydle colony

Chauriagaon

Mehragaon

Suspected spring

Place

Incidence of acute hepatitis by age and sex in 3 villages, Bhimtal block, Uttaranchal, India, July 2005

Population Cases Attack rate

Age 0-4 105 2 2%

(Years) 5-9 110 4 4%

10-14 134 23 17%

15-44 729 139 19%

45+ 261 37 14%

Sex Male 724 115 16%

Female 514 90 17%

Total 1238 205 16%

Person

When to ask for assistance from the state level?

• Unusual outbreak• High case fatality ratio• Unknown etiology• Trigger level three and above

Steps of a full outbreak investigation using analytical epidemiology to identify the source of infection

1. Determine the existence of an outbreak2. Confirm the diagnosis3. Define a case 4. Search for cases5. Generate hypotheses using descriptive findings6. Test hypotheses based upon an analytical study7. Draw conclusions8. Compare the hypothesis with established facts9. Communicate findings10. Execute prevention measures

Requires assistance from qualified field epidemiologist (FETP)

Cohort to estimate the risk of hepatitis by water supply,

Mehragaon village, Uttaranchal, India, July 2005

Cases TotalIncidenc

e

Relative risk

(95% C. I.)

Use of water from suspected spring to drink

No 12 143 9.2% Reference

Partially 13 94 13.8%1.6 (0.8-

3.4)

Exclusively

152 529 28.7%3.4 (2.0-

6.0)

C.I.: Confidence interval

Analytical epidemiology compares cases and non cases or exposed versus unexposed to test the hypothesis generated

on the basis of the time, place and person description

3. Monitoring the situation

• Trends in cases and deaths• Implementation of containment measures• Stocks of vaccines and drugs• Logistics

Communication Vehicles

• Community involvement • Media response

4. Declaring the outbreak over

• Role of the district surveillance officer / Medical health officer

• Criteria No new case during two incubation periods

since onset of last case

• Implies careful case search to make sure no case are missed

5. Review of the final report

• Sent by medical officer of the primary health centre to the district surveillance officer / medical and health officer within 10 days of the outbreak being declared over

• Review by the technical committee Identification of system failures Longer term recommendations

Managerial aspects of outbreak response

• Logistics Human resources Medicines Equipment and supplies Vehicle and mobility Communication channels

• Information, education and communication

• Media Daily update

Control measures for an outbreak

• General measures Till source and route of transmission identified

• Specific measures, based upon the results of the investigation Agent

• Removing the source Environment

• Interrupting transmission Host

• Protection (e.g., immunization)• Case management

Specific outbreak control measures

• Waterborne outbreaks Access to safe drinking water Sanitary disposal of human waste Frequent hand washing with soap Adopting safe practices in food handling

• Vector borne outbreaks Vector control Personal protective measures

• Vaccine preventable outbreaks Supplies vaccines, syringes and injection equipment Human resources to administer vaccine Ring immunization when applicable

Reports

• Preliminary report by the nodal medical officer (First information report)

• Daily situation update• Interim report by the rapid response

team• Final report

Points to remember

1. Outbreaks cause suffering, bad publicity and cost resources2. Constant vigil is needed3. Prompt timely action limits damage4. Emphasis is on saving lives5. Don’t diagnose every case once the etiology is clear6. Management of linked cases does not require confirmation7. The development of an outbreak is followed on a daily basis 8. Effective communication prevents rumours9. Use one single designated spoke person10. Learn lessons after the outbreak is over