L9: Infection prevention Flashcards
How are infections transmitted?
Non-human source to human source
Humans to other humans
- Directly
- Indirectly via vector
Where do infections come from? What are some examples?
Usually a common source
- Environment –> Legionella pneumophila
- Water/ food–> Food poisoning
- Animals–> rabies
What are some examples of direct human transmission?
Influenza
Norovirus
Neisseria gonorrhoea
What is an example of indirect human transmission?
Malaria via mosquitos
Define endemic?
Usual background rate of infection
Define outbreak?
Two or more cases linked in time and place
Define epidemic?
Rate of infection greater than usual rate considering the season
e.g. flu greater in winter than summer, not referred to as an epidemic
Define pandemic?
Very high rate of infection spreading across many regions, countries and continents
Usually a novel agent, no one immune to it (no vaccination etc…)
Everyone susceptible
What is the basic reproduction number?
R0 is the average number of cases one case generates over course of infectious period, in an otherwise non infected, non immune population
What does R0 > 1, R0 = 1 and R0 < 1 mean?
R0 > 1 increase in number of cases, number of cases will grow
R0 = 1 means stable number of cases, stable endemic conditions
R0 < 1 decrease in number of cases, number of cases will die out
What are the reasons for outbreaks, epidemics and pandemics?
New pathogen (pathogen) New host (patient) New practice (practice)
What do we mean by new pathogen?
Noval agents
Old agent but dressed up/ coated in different way
–> antigenic- new antigens on it
What do we mean by new host?
Immune naive people–> without the correct antibodies
New borns–> antibody transfer from mother in last few weeks of gestation–> after 3 months antibodies disappear–> replaced when baby expose to pathogen
–> outbreaks in nursery’s
New places–> exposed to different factors when we go to new places
What do we mean by new practice?
Social practices and healthcare
Tattoos, feeding cattle brain to cattle
What factors determine tranmissibility?
Way it is spread–> direct contact, areosol, muscosal membrane interaction etc
Size of dose required–> how infectious are they? how much of the organism is needed? Varies a lot
Depends on immunity
What do epidemic curves show?
Number of people infected at each time interval over a period of time can be days, weeks, years etc…
Why does it decline?
Either people become immune to the pathogen so less of population affected
OR
People die so there is less of the population to be infected
What model does the epidemic curve form?
SIR models Susceptible Infected Recover Lots of pathogens follow this model, you are susceptible until you have had it then you recover e.g. measles vaccinations
What happens with something such as norovirus?
Peaks over the winter months
Disappears over the summer months
What happens in a smaller poplulation?
Not as predictable, doesn’t follow the epidemic curve
Varying features of outbreaks in smaller population
Stochastic nature–> lots of mini epidemic curves that can overlap or may not overlap
Difficult/ Be careful when interpreting results outcome may/may not be due to intervention
What interventions can we do at pathogen level?
Reduce/ eradicate pathogen
–> Antibacterials including disinfectants
–> Decontamination –> sewage and water separate
–> Sterilisation
Reduce/eradicate vectors
–> Eliminate vector breeding sites
What interventions can we do at patient level?
Improve health –> good healthy, well housed well nutritioned population
- nutrition
- medial treatment
Immunity
- Passive –> maternal antibody, intravenous immunoglobulins–> premature children risk of Respiratory syncytial virus (RSV) given monoclonal antibodies–> protection - children normally get it before the age of two
- Active –> vacciniations
Why do vaccination in large populations work?
Herd immunity
Reduced the risk if infection for those unable to have vaccine
Vaccinated people in contact with infected person do not get infected
Vaccinate proportion of population prevents spread
What intervention can we do at practice and place level to reduce infection?
Avoid pathogen/ vector
–> Associated with geographical region–> don’t go
–> Protective clothing/ equipment (long sleeves , trousers protect against mosquito etc)
–> Personal protective equipment in hosptials
Behaviour
–> safe sex (reduce HIV infection risk)
–> safe disposal of sharps
–> Food and drink preparation–> cooked properly, precautions when abroad etc
Place Environmental engineering --> Safe water --> Safe air --> Good quality housing --> Well designed healthcare facilities
What are the benefits of control?
Decreased incidence or elimination of disease/ organism e.g. smallpox, polio, drancunculitis
What are the negative effects of control?
Reduced exposure–> decreased immune stimulus–> decreased antibody–> increased susceptibles–> outbreak
Vaccination–> increased number of neonates with severe illness because didn’t get antibodies from mother–> vaccinated agaist whooping cough now
Exposure at later average age–> more severe effect
What do we mean by survillance?
What is happening now, here and elsewhere?
What might happen?
