Lecture 25: Introduction to infectious disease epidemiology - Measles Flashcards
What type of diseases are associated with repiratory disease?
Tuberculosis
Covid-19
what diseases are associated with child health?
- Measles
- Malaria
- Tuberculosis
- Diarrhoea
What dieases are airborne?
- Measles
- Tuberculosis
- Covid-19
- Diarrhoea
what disease are transmitted by food and water?
- Diarrhoea
which diseases are transmitted by blood and body fluids?
HIV
what diseases are sexually transmitted?
HIV
what diseases are vector borne?
Malaria
what diseases are bacterial?
- Tuberculosis
- Diarrhoea
what diseases are viral?
- Measles
- HIV
- Covid-19
- Diarrhoea
what diseases are parasitic?
- Malaria
- Diarrhoea
What is measles? how is it transmitted? symptoms?
- a highly contagious, acute viral infectious disease. mostly airborne
- transmitted by respitory droplets and direct contact with nasal or throat secretion of infection persons. can reamin in the air for hours after the person left the room
- characterised by a high fever, runny nose, cough, red watery eyes, Koplik spots
- after several days a maculopapular rash erutps
who is at risk of measles?
- any non-immune person (who has not been vaccinated or was vaccinated by did not develop immunity) can become infected
- unvaccinated young children and pregnant women in particular
- measles is still common in many developing countries - particularly in parts of Africa and Asia
- More than 95% of measles deaths occurs in countries with low per capita incomes and weak health infrastructures
what human interventions can reduce the impact of infectious diseases?
Stable governments
- important for low rates of infectious disease
- health care, vaccination programmes, ensuring good food
National infrastructure
- treated waste discharge
- secure clean water
- food supply
- transport
- communications
- housing
Primary health care
- screening programmes
- vaccination
- access to GPs
Secondary/tertiary health care
- treatment
- prevention of hospital acquired infections
Education
- understand infectious disease transmission/prevention
- support health choices
Public Health
- surveillance (notification)
- outbreak investigation/control
- vaccination programmes
what human interventions are important for controlling measles?
Stable Government
National Infrastructure
- Food supply
- Transport
- Communications
Public Health
- surveillance (notifications)
- outbreak investigation/control
- vaccination programmes
Health care
- Vaccination (stop people getting sick in the first place)
- access to GPs
- secondary and tertiary care
- treatment
- prevention of hospital acquired infections
Education
- understand infectious disease transmission/prevention
- support healthy choices
what is the impact of immunisation?
Shows different numbers of vaccinated people
More vaccinated is harder for the infection to spread, harder to set off an outbreak
Doesn’t reach as many people as not as many people are susceptible
what determines whether there is an outbreak of an infectious disease in a population?
- number of susceptible people
- route of transmission- how the infection is spread
- contacts between people
- the risk of transmission per contact (attack rate)
- how long people are infectious (duration of infectivity)
what is the epidemiological triad?
Host factors:
- infected people
- immune status
- hygiene practices
- nutrition
- age (measles is worse for young and old people)
Environment:
- living conditions
- climate
- socioeconomic factors
- poverty/overcrowding
Agent:
- characteristics for microorganisms for how the infection gets out
There also a vector:
- something where a disease is not by one human to another, but by something else. e.g. mosquito for malaria
what are important things to consider about the agent?
Infectivity:
- the ability of an organism to invade and multiply in a host (% of exposed who become infected)
Pathogenicity:
- the power of the organism to cause sickness in the host once the infection establised (% of infected who develop symptoms)
Virulence:
- the ability of the organism to cause serious disease (% of infected who become seriously diseased or die)
what are the factors of the agent of measles?
Infectivity:
- measles is so contagious that if one person has it, up to 90% of the people close to that person who are not immune will also become infected.. can live for up to two hours in an airspace after an infected person leaves
Pathogenicity:
Very high
Virulence:
- approximately 30% of reported measles cases have one or more complication
- the most serious complications include blindness, encephalities (an infection that causes brain swelling), sever diarrhoea and related dehydration, ear infections, or severe respiratory infections such as pneumonia
- serious complications are more common in children under the age of 5, or adults over the age of 20, pregnant women, people with compromised immune systems
- can have longer-term immunologic consequences
what is the infectios disease framwork?
in a population with no immunity,
1 person infects a few people, who infect a few people, who infect a few people and so on
what is R0?
Basic reproduction number
the average number of individuals directly infected by an infectious case during their entire infectious period, when they enter a totally susceptible population (with no measures in place to reduce transmission)
e.g.
Measles R0 ~15-17 people
Rubella R0 ~7-8 people
Flu R0 ~1.5? people
What is R?
R= the effective reproduction number = the average number of people a person goes on to infect in a population made up of both susceptible and non-susceptible hosts
- the pattern of spread depends on whether
R is <1.0, equal to or >1,0
A disease with reproduction number of 1. Each person only infects 1 person, doesn’t go away but doesn’t get worse either. Less than 1 then the disease will eventually die out. No big outbreaks.
what are the components of the reproductive number?
Number of contacts per time (k)
- contacts where transmission could occur (depends on agent) e.g. coughing
Risk of transmission per contact (β)
- for that particular type of contact
Duration of infectivity (time) (D)
- can start before symptoms
what determines whether there is an outbreak of measles in a population?
The number of susceptibe people
- past infection, immunisation
Route of transmission - how the infection spread
- direct- air borne, droplets
Contact between people
- often frequent (breathing the same air)
The risk of transmission per contact (attack rate)
- very high
How long people are infectious (duration of infectivity)
- ~4 days before and 4 days after rash
- R0 ~15-17
what are the individually focused and public health focused controls?
Individual focus
- trying to decrease the risk of an individual acquiring and transmitting infectious agent
- can be done through vaccination and PPE
Public Health focus
- focuses back at the population level and reduces prevalence and controls drivers of spread
- intervantion at all the three factors that impact R0:
- infectivity (β), Mixing (k) and duration of infectiousness (D)
