Epidemics

Question 0

What is R0 in the context of infectious disease?

Answer 0

R0 = average no. of cases one case generates over the course of its infectious period in an otherwise uninfected, non-immune population

R0 < 1 = decrease in cases
R0 = 1 = stable no. of cases
R0 > 1 = increase in cases

Question 1

What are the different levels of infection in the population?

Answer 1

ENDEMIC DISEASE = usual background rate

OUTBREAK = two or more cases linked in time and place

EPIDEMIC = rate of infection greater than the usual background rate

PANDEMIC = very high rate of infection spreading across many regions/countries/continents

Question 2

What are some general causes of epidemics? Give an example for each.

Answer 2

New pathogen
e.g. Hantavirus in New Mexico -> people migrated to area -> new host for virus

New hosts
e.g. maternal antibodies affected by maternal immunisation, therefore young babies who have not yet been vaccinated for pertussis not protected by maternal antibodies (as the mothers were vaccinated -> did not produce antibodies)

New practice
e.g. changes in socially acceptable sexual behaviour, adding air-conditioning units to buildings, increase in amount of surgery performed

Question 3

What does infectious dose mean?

Answer 3

ID50 = no. of microorganisms required to cause infection in 50% of the population exposed

Question 4

What are some of the problems in analysing small scale outbreaks?

Answer 4

Stochastic nature = more variable and random due to reduced sample size

Question 5

What interventions can be taken to prevent the spread of infection in the population?

Answer 5

PATHOGEN/VECTOR:

• reduce/eradicate pathogen (antibacterials + disinfectants, decontamination, sterilisation)
• reduce eradicate vector (eliminate breeding sites e.g. drain marshland to prevent mosquito breeding -> therefore malaria in UK has R0 < 1)

PATIENTS:

• improved health (nutrition, medical treatment, living standards)
• immunity: passive (maternal antibodies, IV immunoglobulins) or active (vaccinations - herd immunity)

PRACTICE:
- avoidance of pathogen or it vector e.g. avoid geographical areas, wear protective clothing & equipment, practice safe sex, dispose of sharps, hygienic food & drink preparation

PLACE:
- environmental engineering e.g. safe water & air, good quality housing, well designed healthcare facilities (separate rooms v.s. “Nightingale” wards)

Question 6

Explain the concept of herd immunity.

Answer 6

Immunity of a group/community/population to an infectious disease as a result of mass vaccination

The higher the percentage of population vaccinated, the greater the resistance of spread of infection within the population

Question 7

What are some potential consequences of infection control?

Answer 7

Decreased incidence/elimination of disease/organisms e.g. smallpox, potentially polio & dracunculiasis

Decreased exposure to pathogen -> decreased immune stimulus -> decreased antibody -> increased susceptibility -> outbreak

Later average age of exposure -> increased severity of symptoms
e.g. polio, hep. A, chickenpox, congenital rubella syndrome (pregnant women infected with rubella causes foetal defects)

Question 8

What is the role of the local Health Protection Unit of the Public Health of England?

Answer 8

• preparing for public health emergencies
• research in public health
• reporting on public health crises
• collect information on possible sources of infection
• establish whether travellers are at risk
• contact public health authorities overseas