Outbreaks, epidemics, clusters

Question 1

Define outbreak / epidemic

Answer 1

An unexpected increase in the incidence of the disease in a given community / region. i.e. observed cases > expected cases

Outbreak and epidemic are often used synonymously.

Question 2

Define endemic

Answer 2

The constant presence of a disease or infectious agent within a given geographic area or population group.

E.g. malaria is endemic in much of Africa.
Endemic describes attributes of a disease, not an area; ‘endemic area’ if a frequent misuse of the term endemic.

Question 3

Define holoendemic

Answer 3

Endemic disease where children are intensely infected and most adults are immune.

Question 4

Define hyperendemic

Answer 4

A disease constantly affecting a large proportion of all age groups in a population.

Question 5

Define epizootic

Answer 5

Unexpected increase in incidence in an animal population

Sometimes an epizootic infection can reach humans and cause an epidemic (e.g. plague) or fizzles out after causing great alarm but without any epidemic human-to-human trasnmission e.g. H5N1 avian influenza.

Question 6

Define enzootic

Answer 6

Constant presence of a disease in an animal population

Sometimes an enzootic infection crosses to humans and causes an epidemic e.g. SARS, hantavirus, COVID-19

Question 7

Define pandemic

Answer 7

A disease that affects a large number of people and crosses many international boundaries e.g. plague (1900), influenza (1918, 1957, 1968, 2009) and cholera (1961)

HIV and MDR TB are modern pandemics

Question 8

Define cluster

Answer 8

Aggregation of relatively uncommon events or dsieases in space and/or time in amounts that are believed or perceived to be greater than would be expected by chance.

Usually used to describe a cluster of cases of rare (usually non-infectious) disease and often suspected to have an environmental cause.

E.g. cancer cluster