This document discusses hospital outbreak investigations. It defines endemic and epidemic infections in hospitals. Common source and propagated epidemics are described. Steps in investigating outbreaks in hospitals and communities are provided, including forming an investigation team, developing a case definition, conducting epidemiological and laboratory analyses. The goals of outbreak investigations are outlined. Methods for confirming and controlling outbreaks are discussed.

1. Dr D K Niranjan

2.  “A sudden rise in the incidence of a disease”
 The occurrence in a community or region of cases of
an illness with a frequency clearly in excess of normal
expectancy.

3.  Endemic infections in hospital
 Usual or expected frequency of infections in the
hospital (background rate)
 Epidemic nosocomial infections in hospital
 Unusual occurrence of infections clearly in excess of
expected occurrence (background rate)
 Isolation of unusual (rare) organism
 Isolation of organism with different anti-microbial
susceptibility, or molecular typing

4.  Common source epidemics
 Single source or point source
 Continuous or Multiple exposure
 Propagated epidemics
 Person to person spread

5.  Outbreak in Hospital/ Health facility
 Outbreak in Community
 Outbreak in community may have origin in a hospital
 Outbreak in community may trigger outbreak in hospital
 We take almost similar steps to investigate community
and hospital outbreaks
 Infection control programme in hospital may not only
prevent outbreak in hospital, but in community also

6.  Prevent additional cases in the current outbreak
 Prevent future outbreaks
 Learn about a new disease
 Learn something new about an old disease
 Reassure the public
 Minimize economic and social disruption
 Teach epidemiology

7.  Magnitude
 Characterization of cases by time, person and place
 Risk factors
 Source of infection, mode of transmission
 Control of outbreak
 Prevent recurrence
 Document the outbreak – lessons learnt

8.  Epidemiologist
 Clinician/paediatrician/ neonatologist
 Microbiologist
 Member of Hospital Infection Control Committee
 Staff from affected unit/ward
 Others depending on the need

9.  Confirm the diagnosis
 Confirm the existence of an outbreak
 Define at-risk population and characterize the cases by
time, person and place (Case definition; case
ascertainment – identify and count cases; line list of
cases; epidemic curve)
 Review of literature about outbreaks/isolates
 Formulate hypothesis about genesis of outbreak
(source and route of infection)
 Make further investigations to confirm/refute the
hypothesis (case control studies, culture surveys)
 Control the outbreak
 Prepare and disseminate the report (documentation)

10.  Case definition changed
 Introduction of new laboratory tests
 Frequency of testing of patients changed
 Introduction of a new medical or surgical
procedure
 New areas or population included under the
surveillance

11.  Confirm outbreak
 – Confirm diagnoses
 – Case definition
 – Case line listing started
 – Case finding
 – Case interviews
 – Complete line listing
 – Case descriptive epidemiology
 – Establish baseline occurrence of cases
 – Rule out alternative explanations (chance, bias, ...)
 Generate preliminary causal hypotheses

12.  Standard 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
characteristics
 Specific inclusion and exclusion criteria
 Simple, practical, objective
 Suspect, probable, confirmed
 Case definition may be more sensitive initially
 Case definition should be more specific when
sufficient information is available

13.  Identification No.
 Age
 Sex
 Date of admission
 Cause of admission
 Intervention/surgery/procedure done, device used, if any
 Date of undertaking intervention/surgery/procedure
 Place where intervention/surgery/procedure undertaken
 Date of onset of outbreak associated clinical features
 Outbreak associated clinical features
 Lab investigations
 Result of lab investigations
 Diagnosis (Nosocomial infection)
 Outcome: Still ill, recovered, died, other (specify)
 Other relevant variables
 Comments

14. Point source
25
20
15
10
5
0
1 3 5 7 9 11 13 15 17 19
Multiple curves
Continuous source
20 20
15 15
10 10
5 5
0 0
1
3
5
7
9
11
13
15
17
19
1
4
7
10
13
16
19

15. • Who is at risk of becoming ill?
• What is the disease causing the
outbreak?
• What is the source and the vehicle?
• What is the mode of transmission?
Compare hypotheses with facts

16.  Systematically review known causal factors
(Transmission mechanisms and dynamics)
 Prioritize likely causes to guide control
 measures (Step 3)
 Generate testable hypotheses to conduct analytic study
(Step 4) if cause remains unknown or control measure
not working

17.  Epidemiologic/clinical investigation
 Environmental investigation
 Laboratory investigation
 Veterinary or vector borne investigation
 Forensics/Law enforcement investigation

19. Implement control measures
May occur at any time
during the outbreak!!
Control the source of infection
Interrupt transmission
Modify host response
Prevent recurrence

20.  Control measures related to source of infection
 Identify and remove the source of infection
 Isolation of cases
 Quarantine of healthy contacts of infectious disease
 Interrupt transmission
 Protect susceptible host
 Immunization
 Chemoprophylaxis
 Non specific measures
 Surveillance programme for detection/control of
infections
 Risk communication (IEC)
 Research

21. Prepare study protocol
1. Primary question(s)
2. Significance
3. Design
4. Subjects
5. Variables
6. Statistical issues
● Conduct study
● Analyze data
● Interpret findings

22.  Epidemiologic inference
 Validity (internal and external)
 Threats to validity
 Causal inference
– Causal criteria
– Causal models

24.  Detect outbreaks
 Detect public health threats
 Detect infectious cases (case finding)
 Monitor trends in a target population
 Monitor exposed individuals for symptoms
 Monitor treated individuals for complications
 Direct public health interventions
 Evaluate public health interventions
 Generate hypotheses for further evaluation

25.  Communicate preliminary assessments and
recommendations (letter, memo)
 Prepare interim/final reports
 Prepare manuscript (optional)
 Risk communication strategy (what to say)
 Media communication strategy (how to say it)

26. Every outbreak in the
hospitals is an opportunity to
improve infection control
programme. Lessons learnt
should be used to prevent
future outbreaks

27.  Assign a spokesperson who has the authority,
is knowledgeable and respected by community,
health professionals and media
 Give clear, accurate and timely information. Avoid
technical terms, if possible. Update information
regularly.
 Forward 3 positive points against one negative
point.
 Do not allow media to control the entire
dialogue
 Be frank about your efforts and the challenges

28.  Chronology of events - How was the outbreak suspected?
 Methodology adopted for investigation
 Outbreak investigation Team
 Case definition
 Case ascertainment
 Lab investigations
 Epidemiological observations
 Characterization of cases/deaths by time, person and place
 Results of laboratory investigations
 Analysis and interpretation of data collected and compiled
 Further investigations undertaken
 Conclusion about source and route of infection
 Interventions made/recommended
 Dissemination of report including executive summary to all
stakeholders

29.  Viral hepatitis B outbreaks occurred in hospitals in 1980s
and 90s
 In 1997, NICD investigated 3 community outbreaks of viral
hepatitis B
 Mehasana district in Gujarat
 Sirsa district in Haryana
 Sri Ganganagar in Rajasthan
 Inadequately sterilized needles and syringes resulted in
these outbreaks
 Inadequate sterilization still causes many infectious
diseases outbreaks in hospitals
Source: WHO 1998; 76:93-98; Epidemiol Infect 2000;125:367-375

30.  ESI Hospital Colony, Madurai had an explosive outbreak of
chikungunya in September 2009
 Chikungunya cases were admitted to the ESI Hospital
 There was heavy breeding of Aedes mosquitoes in the
campus
 Infection was transmitted to other cases and hospital staff
 9 of 11 doctors and 34 of 37 nurses who worked in the
hospital or stayed in the campus were affected during the
outbreak
 Most of other residents of the hospital colony were also
affected
 Hospital transmission of dengue and chikungunya has been
observed in other cities also in the past

31.  A patient admitted in a hospital probably started
the outbreak
 Infection spread to other patients, visitors and
health acre workers
 66 probable cases, 45 died
 Many including health care workers got infection
in the hospital
 No exposure of cases to animals
 Human to human transmission of Nipah/ Hendra
virus was suspected
Source: IJMR 2006;123: 553-560

32. Thank You