outbreak investigation steps and procedure explained with an example where I investigated an outbreak in a nursing hostel during my post graduation where the students got gastro-intestinal infection. original epidemic curve, spot map are attached along with the slides

1. Investigation of GI infection
outbreak in Nursing Hostel
Dr harjot kaur
MD community Medicine
District Epidemiologist

2. Verification of diagnosis
• The diagnosis of GI infection was confirmed by
examining the cases.
• Signs and symptoms recorded were nausea,
vomiting, diarrhea, abdominal pain, and fever.
• Lab investigation results showed presumptive
coliform count to be positive for the water
sample collected from that area.

3. Confirmation of outbreak
• There were no cases of GI infection before
12th Feb, and there was sudden appearance of
signs and symptoms signifying an outbreak

4. Defining population at risk
• Area involved: nursing hostel
• Population at risk: 478 (hostel resident
students + mess workers + staff)
• At risk: persons drinking same water,
consuming same food

5. Search for all cases
• Medical survey was done to identify each case.
• Epidemiological case sheet: it was introduced to
the hostel residents. It included name, room
number, batch, consumed milk/not, start date of
illness, duration of illness, symptoms (yes/no)
nausea, vomiting, diarrhea, abdominal pain,
previous attack, gone to home (y/n). ECS is
attached with this report.
• All secondary cases were also found and recorded

7. Data analysis
• Time : the data was analyzed with regard to time
trends of the illness. Epidemic curve was made, which
is attached with the report.
• Place: a spot map was prepared after analyzing data in
regard to place distribution. It is attached with the
report.
• Person:
• Age range is between 18-25 years.
• All patients are female (residents of nursing hostel)
• Occupation is student, pursuing nursing and BPT
courses.
• Students often skip meals specially breakfast. Immune
build up seems to be poor. (there is one patient of
tuberculosis diagnosed on 25th Feb, lower immunity
may be one of the factors).

8. Epidemic Curve

11. Spot map

14. Formulation of hypothesis
• Possible source: contaminated drinking water
• Causative agent: presumptive coliform count
is 30 (positive test) but the organism has not
been found yet. That can only be ascertained
after the culture report.
• Mode of spread: feco-oral route

15. Environmental factors which enabled it to occur:
• RO system was no-functional from 6th to 16th Feb
• Cutting of vegetables was being done on floor itself,
food grains were not covered, milk containers were
dirty, milk was having unpleasant smell.
• There was leakage in water supply pipes too, which
was repaired later on.
• Overall, the area was damp, where food was kept in
the mass.
• There was no soaps for hand washing in the washing
area of the mess.

16. • Calculation of attack rate:
• 72 / 478 x 100 = 15%
(total no. of cases/ population at risk *100)

17. Evaluation of ecological factors
• Mess staff was not aware about personal
hygiene, about importance of hand washing.
• Mess area where food was kept was damp,
cleanliness was not there, and food grains
were not covered.
• RO system was no-functional from 6th to 16th
Feb and mess workers used tap water for
cooking purposes in the meantime.

18. Further investigating population at
risk:
• Follow up of all cases is being done regularly,
almost all cases are taking medication and
recovering well.
• More water samples were taken from all over
the campus and they were found positive for
coliform count
Writing a report:
report is attached herewith.

19. Gastro-intestinal infection outbreak
investigation report
Persons contacted: nursing hostel warden, mess
staff, students
Date of contact: 24th Feb. 2015
Report prepared by: Dr. Harjot Kaur (PG Student 2nd
year)

20. Introduction and background:
• Population affected: nursing hostel resident students
of B.Sc. post-basic B.Sc., BPT and GNM courses.
• Location: nursing hostel
• Time of onset: 1st case was reported on 12th Feb. 2015
• Clinical findings: nausea, vomiting, diarrhea,
abdominal pain, fever. Some students also complain of
cough and common cold.
• Suspected factor: it seems to be contaminated water
consumed by students between 6th and 16th Feb.

21. Investigation methods:
• Data collection was done by personal
interviews with the cases, mess staff, warden
and introducing epidemiological case sheet.
• Inspection of the storage place, food grains,
water supply system, milk and other food
items was done.
• A sample of their drinking water was collected
and was sent to lab for testing.

22. Results:
• Epidemiological:
• Cases: a list is attached with this report including
names of the affected students with their batch and
symptoms and other details. Epidemiological case
sheet is also attached with this report.
• Outcome of illness:
• No case was hospitalized
• Few students had gone home (4-5)
• Rests are taking medication and are attending classes.
• No causality was observed
• Most students have recovered.

23. • Microbiological: water sample test results have shown
presumptive coliform count to be positive, but culture
report has yet to come.
• Environmental:
• Washing area where utensils are washed was not
clean.
• RO system was no-functional from 6th to 16th Feb
• Cutting of vegetables was being done on floor itself,
food grains were not covered, milk containers were
dirty, milk was having unpleasant smell.
• There was leakage in water supply pipes too, which
was repaired later on.

24. • Overall, the area was damp, where food was
kept in the mess.
• There was no soap for hand washing near the
basins in the mess.
• No signs and symptoms of any infectious
disease were found among the mess workers

25. Hypothesis:
• Source: contaminated drinking water
• Causative agent: has yet to be determined
based on the culture reports.
• Mode of transmission: person to person, feco-
oral route

26. Actions taken (preventive and control
measures)
• All cases were directed to maintain good personal hygiene
and practice hand washing after going to toilet and before
eating food.
• All cases were taking medication from Adesh hospital.
• Mess staff was directed to clean the water tanks regularly
• Leakage in the water supply pipe was made to be repaired.
• Water coolers were made to be cleaned there only.
• Mess workers were told about using chlorine tablets in case
RO system goes non-functional again. They were told about
how to use the tablets.
• Students were also advised to maintain good immunity, not
to skip meals specially the breakfast.

27. • Mess boys were educating about importance
of hand washing and importance of good
personal hygiene.
• Hostel warden was directed to immediately
report to the authorities if there is problem in
RO system again and they were directed to
use another RO system in that case, which
was present there in the hostel but was not in
use.

28. • Continuous monitoring of the cases and
contacts.
• Continuous examination of mess staff
• Continuous checking of water supply system
• Inspecting milk and other food items in the
mess