6. Epidemiology and Public Health Flashcards
What is an infectious disease?
- An illness due to a specific infectious agent or its toxic product that arises through transmission of that agent or its products from an infected person, animal or reservoir to a susceptible host, either directly or indirectly through an intermediate plant or animal host, vector or the inanimate enviornment
Define:
- An agent;
- Infectivity:
- Pathogenicity:
- Virulence:
- An agent: the entity necessary to cause disease in a susceptible host e.g. bacteria
- Infectivity: the capacity to cause infection in a susceptible host
- Pathogenicity: the capacity to cause disease or clinical symptoms in the host
- Virulence: the severity of the disease that the agent causes in the host
Describe:
- Source of an agent:
- Portal of exit:
- Portal of entry:
- Source of an agent: where the agent originates, lives, grows and multiplies
- Portal of exit: pathway by which the agent can leave the source
- Portal of entry: pathway into the host (often the same as portal of exit)
What is the difference between direct and indirect transmission?
Direct transmission:
- direct contact with soil, plants or infected people
- Mucous membrane to mucous membrane
- Skin to skin
- Across placenta
- Faecal-oral route
- Sneezes and coughs (note these are not indirect as the source must be in very close proximity to the source)
Indirect transmission:
- airborne proper
- vector borne e.g. mosquito
- vehicle borne e.g. objects
- waterborne
What is the incubation period?
- Period between exposure to the agent and the onset of disease
What is the clinical disease?
- Symptoms and signs of infection
- Notification date in surveillance data
What is the latent period?
- Time from infection until infectious period begins
What is the infectious period?
- Time during infection that a person can transmit disease
What is:
- The index case
- The primary case
- Secondary case
The index case:
- The first case in the population (may not always be identified/notified)
The primary case:
- The first identified and/or notified case
- May refer to all cases originating from a point source exposure
Secondary case:
- Case resulting from subsequent transmission
What is reproduction rate?
- The number of cases one case generates on average over the course of its infectious period
- The larger the Ro the harder the disease is to control
- More difficult to detect in a heterogenous population (a population in which not everyone is susceptible)
What is:
- Immunity:
- Herd immunity:
Immunity:
- The capacity of a person when exposed to an infectious agent to remain free of infection or clinical illness
Herd immunity:
- The immunity of a group or community
- Based upon resistance to infection of a high proportion of individual members of the group
Describe:
- Sporadic disease occurrence:
- Endemic disease occurrence:
- Hyperendemic disease occurrence:
- Holoendemic disease occurrence:
- Sporadic disease occurrence:
- a disease that occurs irregularly/infrequently in the population - Endemic disease occurrence:
- constant presence of a disease/infectious agent within a given geographic area/population group - Hyperendemic disease occurrence:
- the constant presence of a disease at a high incidence/prevalence and affects all age groups equally - Holoendemic disease occurrence:
- high prevalent levels of infection early in life, affects most of the childhood population, adults show less evidence of the disease
What is:
- An epidemic/outbreak?
- A pandemic?
An epidemic/outbreak:
- Occurrence of cases in a community or region in clear excess of normal expectancy
Pandemic:
- A very widespread, often global disease outbreak
Describe the disease Salmonella in terms of disease outbreak:
Causative organism: Salmonella enterica
Diseases:
Local- gastroenteritis
Systemic- typhoid (Salmonella enterica typhi)
Reservoir:
- GI tract of many species of animal
- Environment contaminated by feces
Source:
- Contamined food or objects or from infected animal/person
Portal of exit:
- GI tract
- Fomite
Portal of entry:
- Oral: ingestion of Salmonella bacteria
Transmission:
- direct
- indirect
Characteristics of disease timeline:
- Incubation period: 12-72 hours
- Clinical disease: 4-7 days
- Short latent period, very long infectious period (people can be carriers)
Immunity:
- not always induced due to numerous serotypes
Describe Ebola in terms of an outbreak disease?
Causative organism: ebola virus
Resevoir: bats?
Source: bodily fluids of sick/dead person, contaminated objects, infected animals
Transmission:
- Direct and indirect
Portal of exit:
- Bodily fluids secreted by skin and mucous membranes
Portal of entry: penetration of skin and mucous membranes
Timeline of disease:
- Incubation period- 2-21 days (lines up with latent period)
- Clinical disease: death-20 days
- Infectious period: from when clinical disease begins to 2 days post
Immunity:
- no carriers
