Post on 14-Jun-2015
description
Disease Outbreak
Qinghai Medical College
Wang Zhaofen
Oct,27,2005
Investigating an Outbreak---a Challenge for the Disease
Detective1.What is an outbreak?
2.Uncovering Outbreaks
3.Why Investigate an Outbreak?
What Is an Outbreak?
An outbreak, or an epidemic, exists when there are more cases of a particular disease:
1. in an area, 2. among a specific group of people, or 3. over a particular period of
time
Requirements of a Disease Outbreak
1. The presence of a pathogen in sufficient quantities to affect multiple persons
2. An appropriate mode of transmitting the pathogen to susceptible persons
3. An adequate pool of susceptible persons who are exposed to the pathogen . Fig.1
Pathogen
Mode of Transmission
Factors required for the development and maintenance of a disease outbreak
Fig.1
Mode of Transmission in Acute Outbreak of Disease
★Person – to – person
★common-source exposure
Uncovering Outbreaks
Health departments learn about most outbreaks in one of two ways:1. Calls from a physician or other healthcare provider. 2. Public heath surveillance
Why Initiate an Investigation?
Describe the problem Control and prevention
based on scientific evidencePolitical and public concernsTraining of epidemiologists Research--answer scientific
questions
Whether an Investigation Is Warranted?
◇Apparent number of persons affected
◇Presence of unusual or severe clinical symptoms
◇Lack of an obvious explanation for disease
occurrence
◇Perceived need to implement control measures
◇Level of public concern
◇Potential for contributing to medical knowledge
Guidelines for EpidemiologicField Investigations
Prepare for field work Verify diagnosis Confirm epidemic Identify and count cases
create case definition develop line listing
Guidelines for EpidemiologicField Investigations
Tabulate and orient data: time, place, and person Take immediate control measures Formulate and test hypothesisPlan additional studies Implement and evaluate control measuresInitiate surveillance Communicate findings
Field Investigation:Time
Epidemic curve: # of cases by time of
onset Shape of the curve gives you clues:
agent known: use incubation period to
look back at exposure agent unknown, but common event
likely: postulate agent by determining
the incubation period
Field Investigation:Place
Orient to: place of residence place of work activity sites (church, reunions, weddings, etc.)
Spot map: specific residence and/or
exposure within buildings city blocks or neighborhoodscounty or state level
Field Investigation:Person
Thoroughly describe the case group
(things such as age, sex, race) Identify things shared in common
(events, behaviors, etc.)Get information on people who are
NOT cases as well - the population!Compare groups
What interventions could terminate an outbreak?
◆ Removal or elimination of the source of the
pathogen
◆ Blockage of the transmission process
◆ Elimination of susceptibility (eg, through
vaccination or medication )
Thank you