Outbreak investigation, response and control

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Outbreak investigation, response and control

• IDSP training module for state and district
  surveillance officers
• Module 8

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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

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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

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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

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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)

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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

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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

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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

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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

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Objectives of an outbreak investigation

1. Verify
2. Recognize the magnitude
3. Diagnose the agent
4. Identify the source and mode of transmission
5. Formulate prevention and control measures

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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 ofoutbreak 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)

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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

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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
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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

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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

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The balance between investigation and control
while responding to an outbreak
Source / transmission Source / transmission
Known Unknown
Etiology Known Control Investigate Control Investigate
Etiology Unknown Control Investigate Control Investigate
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Steps in outbreak response

1. Verifying the outbreak
2. Sending the rapid response team
3. Monitoring the situation
4. Declaring the outbreak over
5. Reviewing the final report

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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

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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

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Investigating an outbreak
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Acute hepatitis by week of onset in 3 villages,
Bhimtal block, Uttaranchal, India, July 2005
Time
90
Outlying case-patient might have been a source
80
70
60
50
Number of cases
40
30
20
10
0
1st week
3rd week
1st week
1st week
1st week
1st week
3rd week
4th week
3rd week
4th week
3rd week
4th week
2nd week
4th week
2nd week
2nd week
2nd week
May
June
July
August
September
Week of onset
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Incidence of acute hepatitis by source of water
supply, Bhimtal block, Uttaranchal, India, July
2005
Place
Water supply Spring Reservoir Pipeline Attack
rate lt 5 5-9 10
Mehragaon main village
Dov
Mehragaon Hydle colony
Mehragaon
Chauriagaon
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Incidence of acute hepatitis by age and sex in 3
villages, Bhimtal block, Uttaranchal, India, July
2005
Person
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
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When to ask for assistance from the state level?

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

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

1. Determine the existence of an outbreak
2. Confirm the diagnosis
3. Define a case
4. Search for cases
5. Generate hypotheses using descriptive findings
6. Test hypotheses based upon an analytical study
7. Draw conclusions
8. Compare the hypothesis with established facts
9. Communicate findings
10. Execute prevention measures

Requires assistance from qualified field
epidemiologist (FETP)
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Cohort to estimate the risk of hepatitis by water
supply, Mehragaon village, Uttaranchal, India,
July 2005
Cases Total Incidence Relative risk(95 C. I.)
Use of water from suspected spring to drink No 12 143 9.2 Reference
Use of water from suspected spring to drink Partially 13 94 13.8 1.6 (0.8-3.4)
Use of water from suspected spring to drink Exclusively 152 529 28.7 3.4 (2.0-6.0)
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
C.I. Confidence interval
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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

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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

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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

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Managerial aspects of outbreak response

• Logistics
• Human resources
• Medicines
• Equipment and supplies
• Vehicle and mobility
• Communication channels
• Information, education and communication
• Media
• Daily update

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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

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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

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Reports

• Preliminary report by the nodal medical officer
  (First information report)
• Daily situation update
• Interim report by the rapid response team
• Final report

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Points to remember

1. Outbreaks cause suffering, bad publicity and cost
   resources
2. Constant vigil is needed
3. Prompt timely action limits damage
4. Emphasis is on saving lives
5. Dont diagnose every case once the etiology is
   clear
6. Management of linked cases does not require
   confirmation
7. The development of an outbreak is followed on a
   daily basis
8. Effective communication prevents rumours
9. Use one single designated spoke person
10. Learn lessons after the outbreak is over