Epidemiology Lectures for UG

1
Outbreak Investigation,
Response and Control
Dr. Amita kashyap

2 2
Definition of an outbreak
Occurrence 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
(e.g., Measles, Cholera, Dengue, Japanese
encephalitis, or plague)

3 3
Outbreak and epidemic:
A question of scale
Outbreaks
Outbreaks are usually limited,
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

4
4
What does it Require?
A pathogen in sufficient quantities,
A mode of transmission,
And a pool of susceptible people
4

5 5
Sources of information
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

6
6
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 epidemic
potential
Unusual isolate
Shifting in age distribution of cases
High vector density
Natural disasters

7 7
Why Investigate?
1. Verify and Recognize
the magnitude
2. Diagnose the agent
3. Identify the source
and mode of
transmission
4. Formulate prevention
and control measures
5. Public concerns
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

8
8
0
10
20
30
40
50
60
70
80
90
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39
Primary
Case
1st case
at HC
Report
to DMO
Lab
result
Samples
taken
Response
begins
DAY
CASES
Opportunity
for control!
Usual Sequence of events in outbreak
detection and confirmation (I)

9
9 9
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

Epidemic preparedness
Formation & Training of RRT
Regular review of data
Alertness during known ‘outbreak season’
Identifying ‘outbreak prone areas’
Ensuring that these areas have necessary drugs
and materials (including transport media)
Identifying & strengthening the labs
Designating vehicles
Ensuring communication channels

11
11 11
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

12
12
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 Natural disaster • Local, district, state and
centre

13 13
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 of an outbreak
investigation -1/3
1. Establishing a probable diagnosis
2. Confirmation of the existence of
outbreak
3. Define population at risk
4. Search for all cases – RRT (Interim
report by RRT within one week

investigation Actions-2/3
5. Management of cases, and
Monitoring the situation
6. Environmental and
Entomological studies
8. Laboratory studies
10. Implementation of control and
preventive measures
11. Data analysis & interpretation
CONTD.....

investigation Actions-3/3
12. Formulation of hypothesis
13. Testing of hypothesis
14. Declaring the outbreak to be over
15. Final report & its Review within 10
days of the outbreak declared to be over
16. Documentation
a. Report
b. Publication

Unusual
Health Event
No
Yes
Is this an
outbreak
Etiology, Source
& Transmission
known?
No
Yes
Institute control
measures
Further Investigation
Describe outbreak
in terms of TPP
Continued….

Develop Hypothesis regarding
Source, Transmission, Etiology & PAR
yes No
Does the
Hypothesis
Fit with facts
Institute control
measures
Special studies
Remember that outbreak is usually
a sudden & unexpected event!
There is need to act quickly.
A systematic Approach Helps

21
1. Establishing a probable
diagnosis
Hospital/health center visit
Clinical exam/records
Lab. Reports, etc.

22
2. Confirmation of the
existence of outbreak
Comparing data/ previous records –
minimum for 3 years
If no data – use COMMON SENSE!

23
3. Define population at risk
By studying Line - List of cases
Name, Age, Sex, Address
Date of onset of illness
Signs / symptoms
Investigation reports
Treatment taken
Outcome

24
24
4. Search for all cases
Rapid community house to house survey
Pilot survey
Sample size (n) = 4p(1-p)/ L2
Area selection (Affected & surrounding
areas)
Format
Recall period

25
Develop working case- definition
Set of criteria for deciding if a person
should be classified as suffering from
the disease under investigation
Clinical criteria, restrictions of time,
place, person
Simple, practical

26
Case definition
Example-1
Patient older than 5 years with severe
dehydration or dying of acute watery
diarrhoea in town “x” between 15-30
June 2009

27
A
B
C
D
Area wise map of an affected area
E

28
5. Laboratory Investigation
Appropriate clinical specimens
Time of sample collection
Method of collection
Selection of transport media
Labeling
Storage and transportation of samples
District lab / selection of lab

29
Study of environmental conditions
(water, sanitation etc.)
Entomological survey (density of
vectors, Indices)
Study of Zoonotic reservoir (if
required)
6. Environmental, Entomological
& Zoonotic surveys/ studies

30
Person
Place
Time
Cases
0
5
10
15
20
25
1 2 3 4 5 6 7 8 9 10
0
200
400
600
800
1000
1200
0-4 '5-14 '15-44 '45-64 '64+
Age Group
Evaluate information
Pathogen? Source? Transmission?
7.Data Analysis

31
8. Management/ control of outbreak
As per the epidemiological/ clinical
observation manage the cases
Prevent further deaths
Environmental control measures
Strengthen routine & active
surveillance

39
9. Formulation of hypothesis
Based on data analysis and
interpretation
CONTD.....

40
Benefits of an outbreak
investigation-1
i. To control ongoing/current outbreak
ii. To define the magnitude (time, place,
person)
iii. To determine factors responsible
iv. Source and modes of transmission

41
Benefits of an outbreak
investigation-2
v. To evaluate the effectiveness of existing
surveillance activities at local level
vi. To evaluate the effectiveness of
preventive program
vii. To respond to public or political or legal
concern
viii. To prevent occurrence of future outbreaks
ix. To advance the knowledge about the
disease
x. To provide training opportunity

42
42
0
10
20
30
40
50
60
70
80
90
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39
Primary
Case
1st case
at HC
Report
to DMO
Lab
result
Samples
taken
Response
begins
DAY
CASES
Opportunity
for control!
Usual Sequence of events in outbreak
detection and confirmation (I)

43
0
10
20
30
40
50
60
70
80
90
1
4
7
1
0
1
3
1
6
1
9
2
2
2
5
2
8
3
1
3
4
3
7
4
0
Sequence of events in outbreak detection and confirmation (II)
PRIM HC REP RES
SAMP
Response
begins
DAY
CASES
Potential
Cases Prevented

44
Types of report
Initial “First information report”
Full outbreak investigation report
Rapid assessments
Scientific publications (The most
‘Neglected’ action )

45
General framework of an
outbreak investigation report
(1/4)
1. Executive summary
< one page or < 300 words
Structure with subheadings
2. Background
Territory, origin of the alert, time of
occurrence, places, official staff met

46
(2/4)
3. Methods used for the investigation
Epidemiological methods
Case definition
Case search methods, data collection
Analytical studies if any
Data analysis
Laboratory methods
Environmental investigations

47
(3/4)
4. Major observations / results
Epidemiological results (population at
risk, time, place and person
characteristics)
laboratory diagnosis
Environmental investigation results
Current status of transmission, control
measures adopted/ initiated

48
(4/4)
5. Conclusion: Genesis of outbreak
(Diagnosis, source, vehicles)
6. Recommendations

49
Annexes of the report
1 TIME: Epidemic curve
2. PLACE: Map
Spot map
Map of incidence by area
3. PERSON: Table of incidence by age and
sex
4. Analytical study results if any

50
Be technical
 The District Medical Officer and the
Assistant Secretary of Health joined a team
comprised of myself and three field workers
to go to the site of the outbreak that could
not be reached before three days because
of rains
Focus on technical aspects
 The rapid response team initiated the
investigation on 16 March 2009

51
Examples
Avoid negative statements:
 The district medical officer has not even
started programme implementation in this
district
Prefer specific, documented, diplomatic
opportunity statements:
 Review of 6 out of 7 indicators indicated
that the programme is still at an early phase
in the district

52
Get rid of “should”
 Tuberculosis patients should be counselled
 Counsel tuberculosis patients
 Counselling will decrease default rates
Use both
 Counsel tuberculosis patients to decrease
default rates

53
The six “S” of technical writing
1. Simple
2. Short
3. Structured
4. Sequential
5. Strong
6. Specific

54
1. Simple
• Use simple words
• Don’t use jargon technical or statistical
jargon
2. Short
• < 10 pages, < 5 tables / figures
• Use short sentences with one idea each
• Split complex sentences
• Cut unnecessary elements

55
3. Structured
• Have headings, subheadings
• Follow the logic argument
4. Sequential
• Go step- by- steps
• Start each sentence where the
previous ended

56
5. Strong
Use the verb as the centre of gravity
If the verb is weak, the sentence is weak
6. Specific
• Say clearly and exactly what you want to
say
• Do not paraphrase
• Prefer numbers to qualifiers

57
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

58
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

59
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

60
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. Don’t 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

61
61
A Scenario!
A 23 yr old male student; presented at
10:30 PM on 23rd Feb, at the emergency
complaining of a sudden onset of
abdominal cramping , nausea and
diarrhea. He was not severely
distressed, had no fever or vomiting but
was weak.
61

A Scenario!
A No. of other students, all with the
same symptoms, visited emergency
over next 20 Hrs
All treated with Fluid replacement
and rest.
They recovered fully within 24 hrs.
of the onset of illness.
62

Does it warrant an investigation?
Why?
63

The investigation!
Quick information revealed 47 students
out of 1164 college enrollment got
affected by 8 PM on 24th Feb
what is the quantitative measure of the
extent of an outbreak?
No. of New Cases
AR = Persons at Risk
what is the AR for this period?
64

47/ 1164 X 100 = 4%
It was readily apparent, however that
the PAR need to be defined narrowly!
All those reported lived in hostels and
one third of all students were day
scholars! (756 are hostlers)
47/ 756 X 100 = 6.2% (i.e. 50% increase
in AR)
Because the patient’s hostel was
recorded in records AR could be
calculated hostel and sex wise
65

The Hostel of 47 known cases and the AR, as well as the
population and sex of the occupants of each hostel
Hostel Sex PAR No. of Cases AR
1 F 80 19 23.8
2 F 62 2 3.2
3 F 89 0 0
4 F 61 1 1.6
5 F 53 5 9.4
6 M 35 0 0
7 M 63 0 0
8 F 103 4 3.9
9 M 35 1 2.9
10 M 37 0 0
11 F 34 1 2.9
12 M 62 13 21.0
13 M 32 1 3.1
14 M 10 0 0
Total - 756 47 6.2
66

AR (1, 12) = 19+13/ 80+62 = 22.5%
Risk Ratio = AR hostel (1, 12) / AR (Other
hostels) X 100
= 22.5%/ 2.4% = 9.4
AR BY GENGER?
Visit to hostels revealed that not all
students who became ill reported to
emergency.
Seven hostels were randomly selected
for unbaised information!
67

Response to the questionnaire survey by hostels
Questionnaire returned
Hostel Population Number Percent No. of ill St.
5 53 49 92.5 13
6 35 26 74.3 13
7 63 28 44.4 15
8 103 65 63.1 21
9 35 19 54.3 5
12 62 44 71.0 22
Nurses’
hostel
60 60 100 17
Unidentified - 13 - 4
Total 411 304 74.0 110
68
AR = 110/304 X100 = 36.2%

69
AR of hostel 6 and 12 were 0% and 21%
by emergency data but by survey data
both are 50% - Approach for data
collection!
Was emergency data useless?
Is 36.2% the true AR of
gastroenteritis on campus ?
Explain factors why AR estimated from
emergency records were low?
Why more cases from hostel 1 and 12 at
emergency?

Additional information…..
No large gathering of students
Most students ate at college cafeteria
How will you zero down to source of
infection?
70
St. who ate specific meal St. who did not eat specific meal
Ill Well Total AR(%) Ill Well Total AR(%)
Jan 16
Breakfast 52 100 152 34.2 51 94 145 35.2
Lunch 89 150 239 37.2 20 44 64 31.3
Dinner 87 150 237 36.7 23 44 67 34.3
Jan 17
Breakfast 56 105 161 34.8 42 89 131 32.1
Lunch 106 145 251 42.2 3 49 52 5.8 RR!
Dinner 78 130 208 37.5 31 64 95 32.6

So…can you calculate the IP?
Having identified the meal at which the
students most probably were exposed
to the causal pathogen and
Knowing each student’s time of onset of
symptoms; we can!!
71
IP(hrs) No. of Students Cumulative No. of St.
8 22 22
9 11 33
10 18 51
11 8 59
12 42 101

What next?
A follow up survey to obtain
information about particular foods that
251 students ate at lunch on Jan 17!
If students were uncertain about
whether they ate the food in question,
they were not included in the analysis of
the particular food. As a result total of
those who ate or did not eat each
specific item did not equal 251 for all
items
72

Food specific histories of students who ate lunch
at the college cafteria on Jan 17th
Food/ beverage St. who ate Sp. Food /
Beverage
St. who did not eat Sp. Food /
Beverage
Ill Well Total AR (%) Ill Well Total AR (%)
Fish 16 36 52 30.8 87 103 190 45.8
Lamb curry 95 56 151 62.9 7 82 89 7.9
noodle 12 57 69 17.4 92 80 172 53.5
Pineapple kheer 58 54 112 51.8 39 69 108 36.1
Fruit salad 32 39 71 45.1 63 82 145 43.4
Cabbage salad 4 5 9 44.4 95 126 221 43.0
Chocolate ice cream with
vanilla sauce
19 29 48 39.6 80 102 182 44.0
Chocolate ice cream without
vanilla sauce
62 77 139 44.6 39 56 95 41.1
Badam Milk 91 127 218 41.7 12 13 25 48.0
Cofee 10 31 41 24.4 89 103 192 46.4
tea 23 19 42 54.8 78 114 192 40.6
73

74
Tools for Quantifying
The Epidemic
1. Case definition
2. Epidemic curve
Point source (common
source, common vehicle)
Propagated
3. Attack Rate
4. Serial interval/ I P

75
Getting At The Source
1. Mode of transmission
2. Portal of entry
3. Reservoir
4. Vector
5. Vehicle
6. Agent

76
Only work in the field can uncover
the way in which an agent links to a
host in the real world (Environment)
outside of the laboratory.
Snow discovered the waterborne
route as a major mode of
communication of disease, which
turned out to apply not only to
cholera, but also to typhoid fever and
other infections.
Remember:

77
Steps in Investigation
Prepare for field work
Establish existence of outbreak
Verify diagnosis
Define and identify cases
Perform descriptive epidemiology

78
Steps in Investigation
Develop hypotheses
Evaluate hypotheses
Refine hypotheses and conduct
additional studies
Implement control measures
Communicate findings

79
Step 1:
Prepare for
Field Work

80
Only work in the field can uncover the
way in which an agent links to a host in the
real world (Environment) outside of the
laboratory.
Snow discovered the waterborne route as
a major mode of communication of
disease, which turned out to apply not only
to cholera, but also to typhoid fever and
other infections.
Remember:

81
Prepare for Field Work
Investigation
Scientific knowledge--have it or get it!
Supplies, equipment
Assemble your team
Administration
Review local directives or plans
Consultation
Know your role, especially if off-base

Prepare for Field Work
Sample questionnaires
Key community contacts
Laboratory containers and collection
techniques
82

83
Identify Outbreak Team
Epidemiologist
Laboratory workers
Environmental health
specialists
Local health department
Other state agencies

84
Step 2:
Establish Existence
of Outbreak

85
2. Establish the Existence of An Outbreak
Determine if disease incidence is higher than background
level
How do you determine background level ? -surveillance
Reasons for Observed >Expected
Change in reporting procedures
Change in case definition
Increased awareness or interest
Improved diagnostics
New clinician
Change in Population
True increase

86
Questionnaires
Used to collect complete, uniform
histories
Identifiers
Demographics
Clinical information
Risk factors
Administer as soon as possible
disseminate
interview personally
Both cases and controls
Recall bias important
Can summarize on line listing

87
Levels of Illness
Endemic level
Hyper endemic level
Epidemic level
(outbreak)
Pandemic level

88
Step 3:
Verify the Diagnosis

89
Review Clinical Data
Signs and symptoms
Onset dates
Common exposures
Obtain lab results, if any

90
Step 4:
Define and
Identify Cases

91
4. Define and Identify Cases
Outbreak Case Definition:
-Clinical information (signs and symptoms)
- Person
- Place
- Time
Case Definition Sources
Routine reporting:
Use Standard case definitions
Unknown etiology:
Make up your own case definition
make sure everyone uses the same case
definition

92
Establish Case Definition
Criteria to decide whether person is part
of outbreak
time, place, person
clinical criteria
Can change during investigation
Keep loose at first, tighten later

93
Case Classification
Confirmed: laboratory results
Probable: clinical criteria without
lab verification
Suspect: some clinical criteria

94
Identify and Count Cases
Develop a wide network
Initiate active surveillance
Case: meets case definition
Control: exposed, not ill

95
Identify Population At Risk
Survey hospitals
Review surveillance data
Question known cases to identify
others
Review guest lists, enrollment
records, etc.

96
Identify Population At Risk
Survey hospitals, ERs, MDs
Review surveillance data
Question known cases to identify others
Review guest lists, enrollment records,
manifests, etc.

97
Questionnaires
Used to collect complete, uniform histories
Identifiers
Demographics
Clinical information
Risk factors
Administer as soon as possible
disseminate
interview personally
Both cases and controls
Recall bias important
Can summarize on line listing

98
Line Listings
Spreadsheet format
One row = one case
Columns = variables

99
Step 5:
Perform Descriptive
Epidemiology

100
Descriptive Epidemiology
Describe outbreak by
time
place
person
Become familiar with data
Get clues about infectious agent

101
Epidemic Curves: Time
Plot number of cases by onset date
Index case: first case of outbreak
Determine time course and future
course, exposure period

102
Endemic vs. Epidemic
Endemic Epidemic
No.
of
Cases
of
a
Disease
Time

103
• This is the most common form of transmission
in food-borne disease, in which a large
population is exposed for a short period of
time.
Point Source Transmission

104
Point Source Outbreaks
All exposed at one time
Cases occur suddenly after minimum
incubation time
All cases occur within one incubation
period
Outbreak stops unless secondary spread
Curves have steep upslope, more
gradual down slope

105
Continuous Common Source
May begin suddenly or gradually
Cases do not disappear because of
secondary exposure
Curves have gradual or steep
upslope, plateau trickling down
slope, and may repeat

106
Continuous Common Source
Onset Dates of Illness
Indianapolis, 2002
0
1
2
3
4
5
6
7
8
9
10
3/10/02 3/11/02 3/12/02 3/13/02 3/14/02 3/15/02 3/16/02 3/17/02 3/18/02 3/19/02
Onset Date
Cases
Other*
Dietary Staff
Other Staff
Residents

107
• In this case, there are several peaks, and the
incubation period cannot be identified.
Continuing Common Source or
Intermittent Exposure

108
Propagated Outbreaks
Typical of person-to-person
outbreaks
Secondary cases appear one
incubation period after peak of first
wave
Taller successive waves of cases

109
Propagated Outbreaks
Onset Dates of Illness
Indianapolis, 2000
0
1
2
3
4
5
6
7
8
11/21/00 11/22/00 11/23/00 11/24/00 11/25/00 11/26/00 11/27/00 11/28/00 11/29/00 11/30/00 12/1/00
Onset Date
Cases
Food Staff
Medical Staff
Residents

112
Person
Host characteristics
age
sex
Exposures
occupation
food consumption
leisure activities

113
Place
Spot maps
Simple and effective
Identifies-
–Geographic extent of outbreak
–Clustering or pattern

114
Spot Maps: Place
One spot = case
Community
Facilities
Recreational sites
Population density not reflected

115
Time
Draw epidemic curve
No. of cases over time
graphed by date or time of
onset of symptoms
Tells Us:
“Where are we now?”
“What’s the forecast?”
Probable time of
exposure
Epidemic pattern

116
Step 6:
Developing Hypotheses

117
6.Develop Hypothesis
Round up usual suspects!
Type of agent
Source of agent
Mode of transmission
Usual reservoirs
Known risk factors
Exposures that caused disease
Look at person, place and time for clues
Be able to test

118
Develop Hypothesis
Requires familiarity with disease
Hypothesis should be testable
Still clueless?
Talk with cases again
Visit work sites or billeting area
Don’t forget outliers

119
Developing Hypotheses
Type of agent
Source of agent
Mode of
transmission
Exposures
Be able to test

120
Step 7:
Evaluating Hypotheses

121
Analytic Epidemiology
Quantify relationships between
exposures and disease
Test hypotheses about causes
Comparison groups
cohort study
case-control study

122
Evaluate Hypothesis via Analytical
Epidemiology
Determine exposure variables.
Compare ill to not ill.
Construct a 2 X 2 table
Perform Cohort or Case Control Study
Use Cohort study when:
- Population at risk is known
(you have a denominator)
Interview “ill” and “not ill”
Calculate attack rates - “ate” v/s
“didn’t eat”
Put on food-specific attack rate table

123
Cohort Studies
Defined population
Can contact all in timely manner
Calculate attack rate
Calculate risk ratio to determine
risk of contracting illness from
exposure

124
Attack Rates
Calculate for those ill and exposed and
those ill and not exposed
Number of new cases in population during
period
Population at risk x100 at
beginning of period

125
Calculate attack rates
Attack rate = (ill / ill + well) x 100 during a
time period
If there is an obvious commonality for the
outbreak, calculate attack rates based on
exposure status (a community picnic)
If there is no obvious commonality for the
outbreak, calculate attack rates based on
specific demographic variables (hepatitis cases
in a community)

126
Example: Calculation of A R for Food X
Ate the food Did not eat the food
Ill Well Total Attack
Rate
Rate
10 3 13 76% 7 4 11 64%
Attack Rate = ill / (ill + Well) x 100 during a time period
Attack rate = (10/13) x 100 = 76%
(7/11) x 100 = 64%

127
Risk Ratios
attack rate of ill and exposed a/(a+b)
attack rate of ill, not exposed c/(c+d)
>1.0 = increased risk
1.0 = same as chance
<1.0 = decreased risk

128
Case-Control Studies
Population not defined
Select sample groups of cases and
controls
Calculate odds ratio to determine
likelihood of contracting illness
from exposure (see table 6.7)

129
Odds Ratios
Cross multiply and divide
a b
c d
ad
bc
>1.0 = increased likelihood
1.0 = same as chance
<1.0 = decreased likelihood

130
Step 8:
Additional Studies

131
Clinical Specimens
Identifies agent and confirms cases
Obtain results if already collected
Collect specimens if necessary
Type of specimen depends on
suspected agent, nature of
outbreak

132
Collect Clinical Specimens
Containers available from ISDH
to order call 317-233-8104
Must use containers in date!
7A: enteric bacteria, viruses
4A: parasites
5A: pertussis

133
Specimens must be labeled with
patient’s name and collection
date
Indicate on form that specimen
is related to investigation

134
Submission form(s) must be
completed and enclosed with
specimen
Local health department should
collect and transport specimens to
ISDH lab

135
Environmental Investigation
Help explain why outbreak
occurred
Begins when suspected mode of
transmission identified
Identifies vehicle of transmission
Samples: food, water, air

136
Step 9:
Implement Control
Measures

137
Control Measures
Aim at weakest link
in infection cycle
Epi Triad
Infectious
Agent
Reservoir
Susceptible
Host

138
Possible Options
Post-exposure prophylaxis/treatment
Recalling/destroying food
Providing educational information
Closing an establishment
Exclusion (work, daycare, school)
Making public announcements

139
Media Relations
Communication between ISDH and LHD
extremely important
LHD generally handles media calls
within jurisdiction but ISDH can provide
guidance
All media calls to ISDH routed through
Office of Public Affairs

140
Media Calls
Confirm investigation underway
Provide only confirmed or statistically
proven information
Be careful mentioning businesses
Never speculate or provide identifiers
Remain calm and do not be rushed

141
Step 10:
Communicate Findings

142
Investigation Report
Outlines
investigation
Agency
analyzing
questionnaires
writes report

143
Purpose of Report
Prevent similar outbreaks
Identify trends/causal factors
Justify resources used
Serves as public record

144
Report Format
Cover page in memo format
Background
Epidemiologic investigation
Environmental assessment
Laboratory results
Conclusions

146
On Dec.31,2009, the local health
officer of Jaipur, reported the
occurrence of an outbreak of acute
gastrointestinal illness to the District
Health Officer. Dr. X, epidemiologist-
in-training, was assigned to conduct
an investigation.
Investigating an Epidemic:
The Dinner was held at Hotel . Food
was prepared by Chefs of the Hotel. The
Dinner began at 8:00 PM and continued
until 11:00 PM.

147
When Dr. X arrived in the field, he
learned from the health officer that all
persons known to be ill had attended a
dinner at Hotel on Dec. 31, 2004 Family
members who had not attended the
Dinner had not become ill.
Accordingly, the investigation was
focused on the circumstances related to
the supper.

148
148
Q: Is this an Epidemic?
Endemic for the region?
Due to seasonal variation?
Due to random variation?
What might be the agent?
How is this agent transmitted?
What am I looking for?

149
149
Verify the outbreak
Determine whether there is an
outbreak – an excess number of cases
from what would be expected
Establish a case definition
Non-ambiguous (distinct/ clear)
Clinical / diagnostic verification
Person / Place / Time descriptions
Identify and count cases of illness

150
Select the correct case definition
and find the error in the others:
1. All Invitees in Dinner held in Hotel on Dec.31,2004
between 8:00 PM and 11:00 PM; whether they attended
Dinner or not; whether they participated in food
preparation, transport, or distribution or not; whether they
ate or not.
2. Persons who developed acute gastrointestinal symptoms
within 72 hours of eating supper and who were among
Invitees in Dinner held in Hotel Clarks on Dec.31,2004.
3. Invitees who developed acute gastrointestinal symptoms
within 24 hours of the Dinner held in Hotel on
Dec.31,2004 between 8:00 PM and 11:00 PM

151
Select the correct case definition
and find the error in the others:
1. All invitees to the Marriage Dinner held in Hotel on October
21, 2002between 8:00 PM and 11:00 PM; whether they
attended Marriage or not; whether they participated in food
preparation, transport, or distribution or not; whether they
ate or not. Missing definition of sickness
2. Persons who developed acute gastrointestinal symptoms
within 24 hours of eating Dinner on Dec.31,2004 and who
were among invitees of the marriage dinner. CORRECT
3. Invitees who developed acute gastrointestinal symptoms
within 24 hours Dinner on Dec.31,2004. Did not specify that
they went to the dinner

152
Interviews regarding the presence of
symptoms, including the day and hour of
onset, and the food consumed at the
Dinner, were completed on 75 of the 80
persons known to have been present.
A total of 46 persons who had
experienced gastrointestinal illness were
identified.
152

153
Menu:
Baked Vegetable
Malai paneer
Dum Aaloo
Cabbage salad
Paneer Khumb
Raita
Missi Roti/ Plain Roti
Raj bhog
Coffee
Water
Cream salad
Ice cream (van)
Ice cream (choc)
Fruit salad

154
Which menu item (s) is the
potential culprit?
To find out, calculate attack rates!

Attack Rates among?
The foods that have the greatest
difference in the attack rates among
who ate and who did not eat, may be
the food(s) that were responsible for
the illness.
155

156
Attack Rates by Items Served:
Number of persons who ate
specified item
Number of persons who did not
eat specified item
ill Well Total Attack rate
(%)
ill Well Total Attack rate
%
Baked
Vegetable
29 17 46 17 12 29
Malai paneer 26 17 43 20 12 32
Dum Aaloo 23 14 37 23 14 37
Cabbage salad 18 10 28 28 19 47
Paneer Khumb 16 7 23 30 22 52
Raita 21 16 37 25 13 38
Missi Roti 18 9 27 28 20 48
Raj bhog 2 2 4 44 27 71
Coffee 19 12 31 27 17 44
Water 13 11 24 33 18 51
Cream salad 27 13 40 19 16 35
Ice cream (van) 43 11 54 3 18 21
Ice cream
(choc)
25 22 47 20 7 27
Fruit salad 4 2 6 42 27 69

157
Attack Rates by Items Served:
Number of persons who ate
specified item
Number of persons who did not
eat specified item
Ill Well Total Attack rate
(%)
rate %
Baked
Vegetable
29 17 46 63 17 12 29 59
Malai paneer 26 17 43 60 20 12 32 62
Dum Aaloo 23 14 37 62 23 14 37 62
Cabbage salad 18 10 28 64 28 19 47 60
Paneer Khumb 16 7 23 70 30 22 52 58
Raita 21 16 37 57 25 13 38 66
Missi Roti 18 9 27 67 28 20 48 58
Raj bhog 2 2 4 50 44 27 71 62
Coffee 19 12 31 61 27 17 44 61
Water 13 11 24 54 33 18 51 65
Cream salad 27 13 40 67 19 16 35 54
Ice cream (van) 43 11 54 80 3 18 21 14
Ice cream
(choc)
25 22 47 53 20 7 27 74
Fruit salad 4 2 6 67 42 27 69 61

158
Improper cooling of foods
Improper cooking of foods
Improper reheating of foods
Improper holding temperature
of foods
Cross contamination
Infected food handlers, poor
employee hygiene
Major Causes of Food borne Disease

159
Summary
The Epi Approach...
Identify a problem
Investigate and collect data
Describe data in terms of person,
place and time
Formulate a hypothesis
Test your hypothesis

160
Bottom Line...
Collect good descriptive data
Be observant -- Be objective
Keep Authority informed
Be sure to collect data on both the “ill”
and the “not ill”
Ask for help
Disease prevention!

161
Conclusion
An attack of gastroenteritis occurred
following a Dinner at Hotel Clarks.
The cause of the outbreak was
contaminated vanilla ice cream.

Epidemiology Lectures for UG

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Epidemiology Lectures for UG

Similar to Epidemiology Lectures for UG (20)

More from amitakashyap1

More from amitakashyap1 (20)

Recently uploaded

Recently uploaded (20)

Epidemiology Lectures for UG