Epidemic curve plots the number of cases on the y axis and time (in days or weeks or months) on the x axis What time interval you use on the x axis depends on the incubation period and the time period over which cases are distributed. For example, S aureus should be hours, while hepatitis B or TB should be days or weeks. Failure to use the right time interval mqy obscure the temporal distribution. As a rule of thumb, select aunit that is one-eighth to one-third as long as the incubation period. If you don’t know the incubation period, draw several epidemic curves with different time intervals on the x axis. Show the pre-epidemic period in the graph also to show the baseline. Can suggest whether its person to person or common source outbreak A common source outbreak id defined as an outbreak due to transmission from a single environmental or human source. Propagated (continuing) outbreaks are person to person spread. Outbreaks may begin as a commn source and then become person to person spread (e.g., viral gastroenteritis from shrimp consumption that is then spread person to person); most common with food or water borne outbreaks. Provide info regarding when the cases were likely exposed to the source The course of the exposure (limited or ongoing) Can also provide info on seasonal trends
Reservior of an agent is the habitat in which an infectious agent normally lives ,grows , and multiplies .it could be human ,animals,and invironment.
The infectious process, commonly referred to as the "chain of infection", requires the presence of four elements which, like the links of a chain, are all essential and interrelated. These elements consist of: an agent (infecting microorganism), a source of infecting microorganisms, a susceptible host, and a mode of transmission of the infectious agent. The four elements must be present for an infection to occur. 1. THE AGENT The agent may be a bacteria, a virus, a fungus or a parasite. It must be pathogenic, that is, capable of causing disease (infection) and must be present in sufficient numbers (infective dose) to transmit infection. 2. THE SOURCE Sources of pathogenic agents in the hospital include patients, personnel and to a much lesser extent visitors, and may comprise any of the following: · Persons with acute infections · Persons in the incubation phase of an infection · Persons colonized with an infectious agent · Persons who are chronic carriers of an infectious agent Other sources of infectious microorganisms include inanimate environmental objects which have become contaminated, for example: · Patient care equipment · Instruments · Needles and sharps · Surfaces · Medications, etc. The patient's own microbial flora (microorganisms normally present in and on the human body) may also be the source of an infection in a susceptible or compromised host. 3. THE HOST The host is a person who becomes infected after exposure to an infectious agent. Factors which influence the development of an infection include the resistance of the host, the portal of entry, the size of the inoculum (infective dose), and the type and duration of the contact with the pathogen. Resistance to pathogenic microorganisms varies widely from person to person. Some individuals may be immune to, or able to resist, infection by a particular infectious agent. Others, exposed to the same pathogen, may develop clinical or subclinical infection. Still others may become either colonized with the organism, or asymptomatic carriers of the disease. The following host factors may increase an individual's susceptibility (decrease his/her resistance) to infection: · Extremes in age (the very young and the very old). · Presence of chronic diseases/conditions (Diabetes Mellitus, Neoplasia, Leukemia, Anemia, etc.). · Malnutrition, chronic alcoholism, drug abuse. , Other factors which contribute to lowered resistance include: · Antimicrobial, immunosuppressive, steroid and irradiation therapies. · Breaks in the "first line of defense" (skin, mucous membranes), as a result of: trauma; surgery; anaesthesia; invasive procedures; pressure ulcers; etc.. To prevent the transmission of infection within a hospital, it is clear that one of the links in the chain of infection has to be "broken". Of the four links which make up the chain of infection, we have the least control over the agent, the source and the host. On the other hand, we do have a great deal of control over the mode of transmission, the weakest link in the chain, and the easiest to break. By implementing measures that interrupt transmission, we can prevent pathogenic microorganisms from reaching or entering a susceptible host.
At the end of the descriptive analysis it should be possible to: formulate a hypothesis on the type Of infection Exogenous, Endogenous) Identify the source and route of infection suggest and implement initial control measures
Cohort studiesA cohort study is the best technique for analyzing an outbreak in a small, well-defined population. For example, you would use a cohort study if an outbreak of gastroenteritis occurred among people who attended a social function, such as a wedding,
Guidelines for Management of Outbreak in Healthcare Organization
Kingdom of Saudi Arabia
Ministry of Health
General Directorate for Health Affairs – Najran
King Khalid Hospital
An Outbreaks of HAIS infection should be identified
and promptly investigated because of their importance
in terms of morbidity, costs and institutional image.
Early identification of an outbreak is important to limit
transmission among patients by health care workers or
through contaminated materials.
An outbreak is defined AS
Occurrence of more cases of
disease than expected HAIs
outbreak-any group of illnesses
of common etiology occurring in
patients of a medical care facility
acquired by exposure of those
patients to the disease agent
while confined in such a facility.
Occurrence of more cases of disease
more than expected
over a particular period of ( TIME )
in a given area (PLACE )
among a specific group of people
Aim of this Guideline
1.Provide a management protocol of an outbreak
in health care facilities.
2.Early detection of an outbreak and institute
immediate control measures.
3.Assign roles and responsibilities of persons
involved in management of an outbreak.
Aim of Outbreak Investigation
1.Prevent further disease transmission
2. Provide information that can be used to
control the outbreak
3.Prevent similar occurrences in the future
4.Identify populations at risk of a disease
5.Identify modes of disease transmission
Aim of Outbreak Investigation, cont7
6. Evaluate the effectiveness of infection
7. Learn more about a disease, including the
impact of control measures.
8. Share knowledge and findings with other
health professionals by documenting the
outbreak investigations in reports or journal
Steps Of An Outbreak Investigation
1.Verify the diagnosis; identify the agent
2.Confirm that an outbreak exists
3.Search for additional cases.
4.Characterize the cases by person, place, time.
5. Form a tentative hypothesis (best guess at the
6. Institute preliminary control measures.
7. Test the hypothesis.
8. Refine the control measures.
9. Monitor and evaluate the control measures.
10. Prepare and disseminate a final report.
Planning of Outbreak Investigation
Notify the appropriate individuals and
departments in the institution of the problem;
Establish terms of reference for the
This must include
development of an outbreak team.
Infection control must be part of the outbreak
Consult with laboratory
Laptop, camera etc.
1-Verify the Diagnosis;
Identify the agent
Describe the initial magnitude of the
problem and what symptoms got the
facility's attention .
What diagnosis has been established?
What agent (bacterial, viral, other) has
Establish a Case Definition.
Standard set of criteria for deciding whether an
individual should be classified as (case ) or non
(cases ) based on whether or not they meet the criteria
identified for outbreak
Includes clinical criteria and restrictions by
time, place and person.
Must be applied consistently and without bias to
all persons under investigation
Case Definition cont..
Typical clinical features without lab
Fewer of the typical clinical features
2. Confirm that an Outbreak Exists
Use your case definition to find all cases
Based on your knowledge in #1, are the numbers of
cases above what is endemic (usually seen) in the
If yes, consider that an outbreak exists
Total number of cases .?
Do you have an outbreak?
If yes, proceed
If no, reasons why
report will made with justification why this case is not considered
3.Search for Additional Cases
Encourage immediate reporting of cases
(laboratory, physicians, and personnel).
Search for other cases by retrospective record
review, ADM , REFERAL ,lab reports, etc.
Total number of cases:
4.Characterize the Cases
Person - Place- Time.
Draw Epidemic Curve
The Line List
It is an important tool in effective outbreak
management. collecting data that are.
Rows and columns.
Each Row represents a case
Each column represents descriptive factors
or clinical details (i.e. date of birth, onset
•Epidemic curve plots the number of cases
on the –y- axis
• and time (in days or weeks or months)
on the -x- axis
•What time interval you use on the x axis
depends on the incubation period and the
time period over which cases are
What it tells you
Timing of exposure
Course of exposure
Estimating date of exposure
Probable time of
Develop Hypotheses(best guess at the time)
Hypotheses should address
Source of the agent
Mode of transmission (Vector or vehicle )
Exposure that caused disease
Review data to determine common host
factors and exposures.
Implement Control /Prevention Measures
Implement control measures as soon as
possible if you know the source of an
Aim control measures at the specific agent,
source, or reservoir.
Aim control measures at the weak link in the
chain of infection. (mod of transmission )
Monitor and evaluate the control
The control measures will vary depending on the
agent and mode of transmission
but may include isolation procedures or
improvements in patient care Hand hygiene Cohorting
or environmental cleaning.
some outbreaks, you would direct control
measures at reducing the susceptibility of the host.
Immunization against rubella
Malaria chemoprophylaxis for travelers.
Refine the control measures
additional control measures may be added
Destroying contaminated foods . fluids
An infectious staff or food handler could be
removed from the work and treated.
The Descriptive Analysis
This includes identifying a potential exposure
type ,source and route of infection for the outbreak .
testing this hypothesis using statistical methods.
Special epidemiologic studies may be needed
which allows you to test your hypotheses.
Use rates to identify high-risk groups
Numerator = number of case
Denominator = number of people at risk
The nature of the outbreak determines which of
these studies you will use.
Cohort studies .
Small, well defined population
Contact each attendee and ask a series of
Ill Vs not ill Look for source exposure.
Attack rate is high among those exposed
Attack rate is low among those not
Most of the cases were exposed.
Relative risk = mathematical measure of
association between exposure and
Population not well defined
Case patients and comparison group (controls)
questioned about exposure(s)
Compute measure of association = Odds Ratio
IS a mathematical measure of association
OR relationship between exposure and
A case-control study is the most common approach
To test hypothesis .
Communication and Conclusion
During the investigation of an outbreak,
timely, up to date information must be
administration, public health authorities,
and, in some cases, to the public.
Based on all evidence and the results of
an outbreak investigation
A final report describing all aspects of the
investigation should be prepared.
Prepare and disseminate a final report
A final report on the outbreak investigation
should: describe the outbreak interventions, and
summarize the contribution of each team
member participating in the investigation.
should also make recommendations to
prevent future occurrence.
Make the final report. as detailed as
should also be a written report that follows
the usual scientific format of
By formally presenting recommendations, the
report provides a blueprint for action.