Lecture 6 Outbreak Investigation February 2, 2017 ID Epidemiology (BMTRY 713) MUSC Dept. of Public Health Sciences

Infectious Disease Epidemiology BMTRY 713 (A. Selassie, DrPH) February 2, 2017 Lecture 6 Outbreak Epidemiology & Investigation

Learning Objectives 1. Define Outbreak, , , & 2. Describe the purpose of Outbreak investigation 3. List the main steps in outbreak investigation 4. Illustrate epidemic curves 5. Recognizer main types of outbreaks

Outbreak epidemiology

 Study of a or epidemic in order to control or prevent further spread of disease in a population  It is a specific form of descriptive epidemiology intended to identify immediate threat to public health  Requires urgent action

Terminology

 Outbreak—a small localized cluster of cases, usually an infectious disease  Epidemic—the occurrence of cases of a condition in a population in a number greater than expected for a given period of time  Endemic—a constant presence of a communicable disease in a population – Holoendemic: high proportion of children affected, conferring immunity in adults. (e.g. ) – : constant presence in all ages  Pandemic—an epidemic that transcends national boundary extending to much of the world

Selassie AW (DPHS) 1 Lecture 6 Outbreak Investigation February 2, 2017 ID Epidemiology (BMTRY 713) MUSC Dept. of Public Health Sciences

Types of

 Common source – Single source of contamination – Single vehicle • Consider distribution patterns  Point epidemics – Common source, everyone exposed at the same time  Propagated epidemics – Transfer from one to another – Bimodal with secondary cases – Overlapping secondary cases  Mixed – Include both

Point source epidemics (short)

Point source epidemics (Long)

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Propagated epidemics

Means of

 Contact: direct or indirect  Food- or water-borne: ingestion  Airborne: inhalation of contaminated air  -borne: living organism  Perinatal: during pregnancy or at time of delivery

Identification of an epidemic

 Increase in cases of a disease currently reported to CDC  Reports from doctor’s office, hospitals, nursing home, laboratory  May be reported by an individual

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Temporal trends in infectious disease

 Seasonal variation – Vector-transmitted diseases Periodic Trend  Annual variation (Short-term) – Dependent upon the number of susceptible individuals in the community

 Variation over decades – Decrease in and Secular Trend mortality in some (Long-term) – Large number of new occurring

Outbreak investigations

 Usually conducted by facilities or at the local or state public health level

 CDC is consulted for multi-state outbreaks or those requiring special expertise

Steps in conducting an outbreak investigation

https://www.youtube.com/watch?v=ug_JVEEV_TM-  Identify investigative team members and their roles

 Confirm the existence of an outbreak – Compare rates with background levels – Rule out “spurious” factors (Improved surveillance) – Verify diagnoses – Some diseases are so serious that a single case is investigated • Anthrax, human rabies, botulism, polio, bubonic plague

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Steps in conducting an outbreak investigation (2)

 Select a case definition – May include time and place of exposure, laboratory findings, and clinical symptoms. – Initial case definition has a greater emphasis on sensitivity than specificity – Subsequent case definitions may have greater specificity – Classify cases as confirmed and probable

Classification of Cases

A case definition for plague

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Steps in conducting an outbreak investigation (3)

 Identification of cases – Case finding techniques reviewing existing surveillance data, surveying hospitals, asking existing cases if they know others who may have been exposed  Identification of population at risk – Range from very few to many – Those with a common exposure

Determine study design

 Based upon size and availability of the exposed population, the speed with which results are needed, and available resources. – Small enumerable exposed groups – Large enumerable exposed groups – Groups where exposure can be identified but groups cannot be enumerated – Exposed population is unknown

Data collection

 Determine person, place, and time  Survey administration – Variables to define cases – As soon as possible – Look for similarities among respondents

Selassie AW (DPHS) 6 Lecture 6 Outbreak Investigation February 2, 2017 ID Epidemiology (BMTRY 713) MUSC Dept. of Public Health Sciences

Complementary analyses

 Laboratory studies  Environmental assessment  Implement control measures

Terminology confusion: “Cluster” v. “Outbreak” v. “Epidemic”

CDC: “A cluster is a group of cases in a specific time and place that may or may not be greater than the expected rate.”

OK, so what is an “outbreak” and what is an “epidemic”?

Notes: 1. No national experts define a “cluster” or “outbreak” or “epidemic” in numerical (numerator or denominator) terms (too many variables). 2. Most experts use “outbreak” and “epidemic” interchangeably.

Terminology confusion: “Cluster” v. “Outbreak” v. “Epidemic”

“I can’t define pornography, but I know it when I see it.”

- US Supreme Court Chief Justice William Rehnquist (as quoted by Dixie Roberts)

Selassie AW (DPHS) 7 Lecture 6 Outbreak Investigation February 2, 2017 ID Epidemiology (BMTRY 713) MUSC Dept. of Public Health Sciences

Example: Cases or Cluster?

Are these 5 pertussis cases a cluster? Case Load

5 - Most would say “yes” re: workload and epi 4 - ( # of cases at a single point in time and > endemic Endemic level level, espec. if epi-linked). 3 -

2 -

1 -

wk.1 wk.2 wk.3 wk.4

Example: Cases or Cluster? Are these 3 cases: sporadic, a cluster, or even an outbreak? Case Load Most would say “no cluster” 5 - (only 3 cases at a single point in time but not >than endemic level) 4 - [unless ALL are epi-linked] Endemic level 3 -

2 - Epi-link to 20 case “” 1 -

wk.1 wk.2 wk.3 wk.4

Example: Cluster or Outbreak? Are these 5+ cases a cluster or outbreak?

Case Load Prob. just a cluster (espec. if all are epi-linked), 5 - since outbreak/ epidemic requires increased 4 - incidence AND propagation with time. Endemic level 3 -

2 - “Index case” 1 -

wk.1 wk.2 wk.3 wk.4 wk.5

Selassie AW (DPHS) 8 Lecture 6 Outbreak Investigation February 2, 2017 ID Epidemiology (BMTRY 713) MUSC Dept. of Public Health Sciences

Example: Cluster or Outbreak? Are these 10 cases a cluster or outbreak? Case Load

Prob. an outbreak 5 - (espec. if epi-linked), since outbreak 4 - requires increased Endemic level incidence AND 3 - propagation with time.

2 - “Index case” 1 -

wk.1 wk.2 wk.3 wk.4 wk.5

Waccamaw Pertussis Outbreak April - Sep '03 Epi curve using DHEC Waccamaw case definition

21 “Outbreak” “Epidemic” 18  # early in…  #s and later

15 on…

12 es Cas 9

6

3

0 5/4/2003 6/1/2003 6/8/2003 7/6/2003 8/3/2003 9/7/2003 4/27/2003 5/11/2003 5/18/2003 5/25/2003 6/15/2003 6/22/2003 6/29/2003 7/13/2003 7/20/2003 7/27/2003 8/10/2003 8/17/2003 8/24/2003 8/31/2003 9/14/2003 Week of Onset

Incident Command in “Cluster” v. “Outbreak”

 Cluster: suggests local  area management & command

 Outbreak/ Epidemic: requires local and area, as well as Central Office, management & command w/  coordination/ collaboration

Selassie AW (DPHS) 9 Lecture 6 Outbreak Investigation February 2, 2017 ID Epidemiology (BMTRY 713) MUSC Dept. of Public Health Sciences

Public Perception

Sporadic case: a wisp of smoke

Several cases: a few flames

Cluster: a fire (small or large)

Outbreak: a large fire that’s spreading

Epidemic: a major conflagration(s)

Formulate and Test the Hypothesis  Assess data formally using descriptive and analytic epidemiologic techniques  Test the hypothesis to determine the source of transmission and the vehicle of the agent (Food, water, milk, etc.)  Assess the hypothesis to determine risk factors. – (E.g., Are those who attended the wedding luncheon at higher risk than those who did not attend the luncheon?)

Summary

 Outbreak investigations are intended to gain information about disease, , and risk factors so that urgent preventive measures will be implemented  Involve series of well-planned and executed steps and methods  Cooperation and communication are key elements

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