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