Disease Outbreak Investigation and Response

What are the leading causes of death among children under 5?

Leading Causes of Childhood Deaths

Source: WHO estimates of the causes of death in children, 2000-03 Bryce, Lancet, 26 March 2005

Where do 10 million children die each year?

WHO estimates of the causes of death in children, Lancet, 2005

What are the major causes of under 5 deaths in emergency settings?

Major Causes of Death in Emergencies for <5 Years

Sudan: Wad Kowli CampFebruary, 1985

Somalia: Gedo Region 7 Camps, January, 1980

Source: Centers for Disease Control and Prevention, Famine-Affected, Refugee, and Displaced Populations: Recommendations for Public Health Issues. MMWR, 1992;41(No. RR-13):8.

MeaslesARIMalariaDiarrheaOther

Examples of Recent Outbreaks

Cholera – Kenya, South Sudan Measles – Aceh, South Sudan, Kenya Yellow fever – South Sudan Meningitis – Darfur Hepatitis E – Darfur Dysentery – Liberia Malaria – Ethiopia, Uganda

Outbreak Investigations

Why investigate an outbreak?

When to investigate?

How to investigate?

Why investigate an outbreak ?

Public Health rational

• To design control and preventive measures

• To reduce morbidity

• To reduce or prevent mortality Delayed or improper interventions = DEATHS

Investigation allows us to (1):

Identify the causative agent• New pathogen causing new disease, e.g. HIV 1984..• Old pathogen causing this outbreak (e.g. Hep E,

salmonella)• Toxic substances (e.g. insecticides, heavy metals, etc.)

Identify modes of transmission• Design effective and efficient interventions

Identify who is at risk• Geographic location• Age or sex group• Occupation• Other

Investigation allows to (2):

Evaluate health services (e.g., vaccine efficacy) Evaluate public health interventions Evaluate the surveillance system

• Sensitivity, specificity etc. Contribute to medical knowledge Communicate and advocate

TAKE ACTION: disease control and prevention

Investigation requires:

Basic medical & public health knowledge Basic concepts of epidemiology Sources of specialized information (e.g. reference

books & specialists) Knowledge of the environment Laboratory testing (but not always) COMMON SENSE !

But before investigating an outbreak…

PREPARE for an outbreak if it is likely!!

Steps in Investigating an Outbreak

1) What are the steps in investigating an outbreak?

Steps in Investigating an Outbreak (1)

1) Establish the existence of an outbreak

2) Confirm the diagnosis

3) Define a case and count cases

4) Perform descriptive epidemiology (person, place and time)

5) Determine who is at risk

6) Develop hypotheses explaining exposure & disease

Steps in Investigating an Outbreak (2)

7) Evaluate hypotheses

8) As necessary, reconsider/refine hypotheses and execute additional studies

• additional epidemiologic studies

• other types of studies – laboratory, environmental

9) Communicate findings

• written report

• presentations

10) Implement control and prevention measures

Confirm the Existence of an Outbreak

Definition of outbreak

• One case – for diseases of epidemic potential (e.g., measles, cholera)

• More than the expected number of cases – for endemic diseases

• Sometimes is quantitative threshold (e.g.meningococcal meningitis)

Importance of a good surveillance system for early warning

Monthly malaria admissions and rainfall, Wajir,1996-98

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Substantial Rise in Malaria Cases

Weekly incidence of meningitis, MSF/MOH/Epicentre, Mali, 1997

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Confirm the Diagnosis

Talk with health workers Examine cases yourself ! Laboratory testing (e.g., malaria, cholera,

hemorrhagic fevers, etc.)

Exaggeration of reported outbreaks is common

Develop a Case Definition

Must be easily applied by health workers

• Preferably does not require laboratory results

• Short time with each patient Must be standardized Should be relatively sensitive

• Detect most cases

• May pick up false positives

Develop a Case Definition

Measles: 3 possible case definitions Fever and runny nose? Fever and rash and Koplik’s spots and

conjunctivitis? CDC case definition: generalized maculopapular

rash > 3 days and fever and at least one of the following: cough, coryza or conjunctivitis?

Develop a Case Definition

Measles: 3 definitions Fever and runny nose

• Too sensitive• Too many other illnesses produce same symptoms• Call many illnesses “measles”

Fever and rash and Koplik’s spots and conjunctivitis

• Too specific• Many cases of measles do not have all these signs• Miss many real cases of measles

CDC case definition: generalized maculopapular rash > 3 days and fever and at least one of the following: cough, coryza or conjunctivitis

Develop a Case Definition

Sometimes define levels of certainty regarding diagnosis; for example, meningitis or Ebola

Confirmed case: laboratory confirmed

Probable case: fits all components of clinical case definition

Possible case: suggestive clinical signs but not fit case definition

Once Case Definition is Established

Count cases !

Reinforce passive surveillance Active case finding

You do not have to count all cases, but

• What proportion should be detected?

• Depends on what you do with data

Descriptive Epidemiology

TIME, PLACE, PERSON May be possible to answer:

• Who is at risk?

• What is source of infection?

• What is mode of transmission?

Descriptive Epidemiology - Time

Distribution of cases by date of onset

X axis: time Y axis: number of cases

Shows:• Time limits / duration of the outbreak• Peak / incubation period• Form of curve: evolution of outbreak• Formulate hypothesis regarding source

Epidemiologic Curve

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Descriptive Epidemiology - Person

Numerators

• Describe cases in terms of • age, sex, • other parameters : refugee / displaced /

residents• immunized , not immunized

Denominators

• Distribution in the overall population (age, sex,...) Compare rates to identify high risk groups

Descriptive Epidemiology - Place

Map cases: identify geographic places at risk

Determine where disease acquired: Home, work, travel, etc..

John Snow’s Map of Cholera Cases

Yambuku 4.5Yamolembia 2.6 Yamisole 2.7

Badjoki 1.8

Bongola 1.6

Yalosemba 1.0

Yaeto-Liku 1.3

Yasoku 0.2

Yambala 0.7Yambala 0.1

Kokoko 0.8 Modjambole 0.8

Yapiki 0.7

Ebola epidemic, Yambuku, Zaire 1976

Information to Collect on Cases

Personal information Age Sex Place of residence (address) Other relevant “exposures”

• Refugees vs locals

• Food source

• Water source Ethnicity, religion, etc.

Information to Collect on Cases

Disease data Date of onset of symptoms Clinical symptoms and signs Immunized or not (measles, meningitis) Laboratory results (if any) Duration of disease, outcome (death, cured,..) Treatment received

Develop Hypotheses

Often obvious from descriptive epidemiology Formulate idea about source of outbreak and

mode of transmission

Test Hypotheses

Cross – sectional study? Cohort study Case – control study

• Identify cases

• Select control group• Possibly matched on age or sex or location• Community control, clinic control etc.

• Compare exposures among cases and controls

• Calculate odds for various exposures

Write a Report

Clarifies your own ideas / synthesis Presents data and conclusions to anyone

interested

• Often epidemiologist don’t implement interventions

• Must communicate to those who will intervene Advocacy: MOH, UN, other NGOs, donors Basis for future reference

Implement - Take ACTION

Interventions include Prevention of further cases Control of transmission and source of infection Improve case management, lower case-fatality

rate

What would SAVE’s role be in responding to an outbreak?

Outbreak of acute watery diarrhea confirmed as cholera?

Large cluster of measles cases in displaced persons camp?

Sharp increase in measles cases in which SAVE is supporting clinical services ?

What preventive measures can be taken to reduce likelihood of an outbreak?

Measles? Cholera? Dysentery? Meningitis? Malaria?

Exercise

SAVE supports clinical services in a large IDP camp with 75,000 persons. A large number of cases of acute jaundice syndrome is detected and local physicians suspect hepatitis. Your clinicians report several deaths among adult women.

What would you do to investigate or confirm this?

Exercise – part 2

Laboratory confirms agent is Hepatitis E. Over 1000 cases have been reported at your clinics. You suspect there are more cases in the camp that have not come to the clinic.

What other epidemiologic information would you like to see? What environmental information?

What would you do about those not coming to the clinics?

Exercise part 3

An active case search is conducted and more than 3500 cases are detected. Water sources include water from distribution system (sometimes chlorinated), hand pumps. Some persons collect water from streambeds. There are approximately 100 latrines in the camp.

What do you recommend on the prevention

side?

Example part 4

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Steps Taken

Chlorination of all water sources (week 32)

Latrine construction Hygiene promotion and

soap distribution Active surveillance