Describe infectious disease epidemiology Flashcards
(35 cards)
What is an epidemic
An outbreak; an increase in the number of cases of an infection over and above expected levels
Or a single case or small number of cases of an unusual organism
what is an pandemic
- Epidemic involing more than one country
name example of pandemic
- Swine H1N1 flu pandemic 2009
- European measles pandemic 2009
- Ebola outbreak 2014-15
what is incidence
- Incidence is a measure of the probability of infection
what is prevalence
- Prevalence is the proportion of infection found to be affecting a particular population
what is the incidence rate
- The incidence rate is the number new cases per population at risk in a given time period
what is the difference between incidence and prelevance
Incidence conveys information about the risk of contracting the disease whereas prevalence indicates how widespread the disease is
What is the source of infection
Environment – food, water, soil, airborne
Animals – zoonosis, animal carrier, vector-born
Humans – human carrier – symptomless and convalescent – some people are just carriers
How are pathogens transmitted
General transmission
- Abiotic environment factors; wind, water, inhalation of spores, entry into skin
- Animal vectors – mosquitos, malaria, dengue, fleas(bubonic plague)
Human to human transmission
- Direct contact – pathogen survives best inside the body such as herpesviruses Ebola
- Indirect contact – pathogen survives harsh environment, pick up pathogen from surface or air such as influenza, norovirus
- Droplets- pathogens are in droplets but do not survive long this way, for example Ebola, Bordetella pertussis
- Airborne – pathogens aerosolized and stay infected such as influenza tuberculosis
- Faecal and oral – through contaminated water or food such as cholera, norovirus, shigella
what is the transmission terminology
- Index – the first case identified
- Primary – the case that brings the infection into a population
- Secondary – infected by a primary case
- Tertiary – infected by a secondary case
what are the three factors influencing disease transmission
- Agent
- Host
- Environment
what is the agent influencing disease transmission characteristics
- Infectivity – how infectious is the virus
- Pathogenicity – if you kill the host too quickly then it doesn’t spread very far
- Virulence -
- Immunogenicity – how immunogenic it is, how easily it can escape the immune system
- Antigenic stability
- Survival
what are the characteristic of the host influencing disease transmission
- Age
- Sex
- Genotype
- Behaviour
- Nutritional status
- Health status
what are the characteristics of the environment influencing disease transmission
- Weather – some viruses are seasonal like flu
- Housing
- Geography
- Occupational setting
- Air quality
- Food
what is the animal full of disease
- Bat – biggest reservoir for Ebola, other mammal species are infected and these infect humans in different ways
describe breakouts in Ebola
- Simultaneous outbreaks in 1976 in DRC (318 cases, mortality rate 88%) and Sudan (284 cases, mortality rate 53%)
- Sudan index case – cotton factor workers or spread by use of contaminated needles among member
- Named after a small river in northwester DRC
Chronologoy of elbola viruse disease outbreak
2013-15
- Countries Guinea, Sierra Leone, Liberia, cases 28,646, case fatality 39.5%
what was the index case in ebola
- More close population easier that it will spread
- Idex case – boy aged 2, got ebola after the symptoms he died within 2 days, but before he died he transmitted it to his sister, his mother and family friend
- Then it was transmitted to the grandmother – she was a nurse and midwife who travelled between towns so it spread between towns, millions of people caught it
how is ebola transmitted
- Transmission is blood secretions
- Skin abrasion
- Needle stick
- Mucosal surfaces
Spread after primary infections to the lungs and reticuloendothelial cells
what are the symptoms of ebola
- Day 7-9 = headache, fatigue, fever, muscle soreness
- Day 10 – sudden high fever, vomiting blood, passive behaviour
- Day 11 – bruising, brain damage, bleeding from nose, mouth, eyes, anus
- Day 12 = loss of consciousness, seizures, massive internal bleeding, death
what was the ebola outbreak not controlled
- Poor countries
- Fragile healthcare systems
- High rate of infected healthcare workers
- Movement across porous borders
- Lack of leadership
how does survicielnce and ring vaccinations work
Contact tracing
- Sick individual are ased to identify contract, authorities attempt to find and isolate contact\
- Hard in urban environments because of unknown contacts
- Sick individuals have a long time to infect others before being hospitalised
Community monitoring
- Communities with infected individuals monitored daily, effective due to early identifications of infections
- Sick individuals are isolated before they have a chance to infect others
Now have a recombinant vaccine, it was used in 2017 but we still don’t know the extent to which it is working, around 50% of people given the vaccine had only mild disease
- Need to be tested in big numbers of people
Identify the index case, primary infection and secondary infection
describe the history of influenza
- 412BC – first mentioned by Hippocrates
- 1580 – first pandemic described
- 1580-1900 – 28 pandemics
- First isolated in the UK in 1933
- Influenza recovered from throat washes of an infected ferret
describe influx epidemiology
- Yearly infections infect 15-20% of the world’s population
- 3-5 million severe cases
- 250-500,000 deaths/year
what is the mode of transmission of influenza in humans
- droplet infection
