1 Global Health- Infectious Diseases

Question 1

Q: What does epidemiology require a clear definition of?

Answer 1

A: ‘case’

=person with disease, health disorder or suffering from event of interest (not necessarily same as clinical definition)

Question 2

Q: What does prevalence mean? What is it also known as?

Answer 2

A: frequency of disease in a population at a point in time
(its a proportion- measure of disease occurrence)

point prevalence

Question 3

Q: How is prevalence calculated?

Answer 3

A: number of cases in population/number of people in polulation

Question 4

Q: What measure of disease occurrence can be obtained from cross sectional studies?

Answer 4

A: prevalence

Question 5

Q: What can prevalence be used to compare?

Answer 5

A: burden of chronic disease between populations

Question 6

Q: How can incidence be interpreted?

Answer 6

A: as the probability, or risk, that an individual will develop the disease during a specific time period

Question 7

Q: How do incidence and prevalence differ?

Answer 7

A: Incidence measures NEW CASES while prevalence measures ALL CASES (new and old)

Question 8

Q: What is prevalence dependent on? (2)

Answer 8

A: number of new cases (incidence), and the time that they remain cases before they die or recover (duration of disease)

Question 9

Q: When do individuals leave the “pool” of prevalent cases?

Answer 9

A: when they recover or die

Question 10

Q: What is the equation to calculate incidence? What else does an incidence estimate require? Provide examples in relation to Ebola.

Answer 10

A: new cases during time period under question / (denominator) total population at risk at start of time period (eg. all the people living in Sierra Leone during this time period)

accurate test to define a true case (eg. a blood test for Ebola is either positive or negative and if it was newly positive this suggests a new case or incident infection)

Question 11

Q: How does incidence influence policy makers using Ebola as an example?

Answer 11

A: In the case of Ebola, once incidence has reached near zero we declare the outbreak over and can reopen schools etc

Question 12

Q: If incidence stays the same, how can prevalence go up?

Answer 12

A: prevalence can go up if you are keeping people with the condition/ disease alive(i.e. HIV treatment now available)

Question 13

Q: What is mortality defined as?

Answer 13

A: The number of deaths from a specific disease/ condition in a given time period

Question 14

Q: What is the calculation for mortality?

Answer 14

A: deaths from a disease in given time period/ population at start of time period

Question 15

Q: In relation to mortality and incidence, when is the epidemic defined as stable?

Answer 15

A: mortality = incidence

Question 16

Q: How are more HIV sufferers kept alive? What is the issue with mortality equalling incidence (epidemic is stable)?

Answer 16

A: Antiretroviral therapy (ART)

treatment= more people kept alive= mortality reduced and potentially people are alive longer, they can

– transmit virus to sexual partners and their babies and incidence may go up
– prevalence increases as more cases are transmitted as well as people not dying

Question 17

Q: What is morbidity defined as?

Answer 17

A: The number of cases of ill health, complications, side effects attributed to a particular condition over a particular time period

Question 18

Q: How is the difference between mortality and morbidity explained in terms of what they refer to?

Answer 18

A: Morbidity= the state of being diseased or unhealthy within a population. Morbidity refers an incidence of ill health in a population

Mortality= the number of people who died within a population. Mortality refers to the incidence of death or the number of deaths in a population.

Question 19

Q: Who are assigned scores / predicted morbidity?

Answer 19

A: ill patients

Question 20

Q: Which systems help the assigning of scores / predicted morbidity? (6)

Answer 20

A: APACHE II, SAPS II and III, Glasgow Coma scale, PIM2, and SOFA

Question 21

Q: What does the use of assigned score / predicted morbidity help? What do they describe and why is this useful?

Answer 21

A: Help decide kind of treatment or medicine that should be given to patient.

Predicted morbidity describes the morbidity of patients, and is also useful when comparing two sets of patients or different time points in hospital

Question 22

Q: How are mortality rates normally expressed?

Answer 22

A: as number of deaths per 1000 individuals per year

Question 23

Q: What is the highest death rate and where is it?

Answer 23

A: 30.83 in Swaziland (2009)

Question 24

Q: What are the 5 leading causes of death?

Answer 24

A: heart diseases, cerebro-vascular disease, respiratory infections, HIV/AIDS, COPD

Question 25

Q: in third world countries 58% of the mortality reported was due to what?

Answer 25

A: malnutrition or deficiencies

Question 26

Q: What are the top 6 leading causes of infection?

Answer 26

A: Lower respiratory infections
HIV/ AIDS
Diarrhoeal diseases
Tuberculosis
Malaria 
Measles

Question 27

Q: What is the leading cause of death in sub-Saharan Africa?

Answer 27

A: Infectious disease

Question 28

Q: 4 of the 10 leading causes of death are infectious diseases in which income countries?

Answer 28

A: low- and middle-income countries

Question 29

Q: 9 of the 10 leading causes are non-communicable diseases which income countries?

Answer 29

A: high-income countries.

Question 30

Q: Why are age standardised death rates important?

Answer 30

A: in assessing effectiveness of country’s health system

Question 31

Q: What are age standardised death rates?

Answer 31

A: weighted average of the age-specific mortality rates per 100,000 persons, where the weights are the proportions of persons in the corresponding age groups of the WHO standard population

Question 32

Q: Where do most preventable deaths in children occur?

Answer 32

A: in low- and middle-income countries

Question 33

Q: Identify the current burden of infectious diseases. (7)

Answer 33

A: SAR event 2003
West Nile Virus 1999
HIV 1 (1982) -> RNA virus 1982
Malaria
MERS virus
Ebola Epidemic (Ebola Virus disease-EVD)
Zika virus

Question 34

Q: West Nile Virus. Origin? Infection rate? Morbidity? Vaccine?

Answer 34

A: • Origin is from birds (Crows/Rooks)
• Has a high infection rate
• Low serious case of morbidity
• Vaccine for this is nearing the end of its clinical trial and should be in production soon

Question 35

Q: SAR virus origin?

Answer 35

A: Bat in Central Asia

Question 36

Q: HIV 1 -> RNA virus. Epidemics over time? Treatment? Vaccine?

Answer 36

A: • The epidemics are increasing in a more linear manner and should start to flatten out
• Integrase inhibitors are being used (using triple therapy-3 types of treatment in one)  considered very effective
• Billions have been spent in terms of producing vaccine but nothing sufficient has been produced as RNA viruses have no proofreading mechanisms increasing the chance of mutation and evolutionary progression

Question 37

Q: Malaria. Genetic variation? Vaccine?

Answer 37

A: • Generation of genetic variability-> mutation and recombination of different gametes, Plasmid transfer
• Plasmodium virus has multiple surface antigenic proteins as each one synthesised is slightly different, this makes It harder to target in terms of vaccine production

Question 38

Q: MERS virus. Origin? Incidence?

Answer 38

A: • Origin is from Camels and has a high incidence in the Middle East

Question 39

Q: Ebola. Transmission? Symptoms when? Contagious? Spread how? Public health measures?

Answer 39

A: • Has a slow characteristic of transmission
• Tend to get symptoms before you are highly infectious allows patient to be placed in isolation before the virus transmits to anyone else
• It is highly contagious and rapidly fatal, but it can be prevented
• It is spread through direct contact with body fluids such as blood, saliva, urine, semen, etc. of an infected person and by contact with contaminated surfaces or equipment, including linen soiled by body fluids from infected person

• Public health measure
o Identification, isolation and follow up of contacts

Question 40

Q: Zika virus. Initially isolated? Association? Transmission?

Answer 40

A: • Was initially isolated from Rhesus Monkeys
• An association has been linked with Microcephaly in infants born to infected mothers
• This virus is a flavivirus and is transmitted by Mosquitoes

Question 41

Q: What are the origins of human infection?

Answer 41

A: 1) Inherited form our ancestors

2) Acquired from wildlife
3) Acquired from livestock

Question 42

Q: What is the focus on new epidemics? (5)

Answer 42

A: • To indicate emergence of infectious disease-> morbidity/mortality in space and time (this is hard to assess)
• Look for international databases to look for homogeny in cases/study results worldwide-> allows you to identify Aetiology
• Diagnostic tests-> analysing blood tests and using antibodies OR you could use PCR to amplify small parts of the virus to determine genetic sequencing
• Follow the routes of infection
• Ensure the public are aware of new information, this can allow wide spread initiatives to be implemented in terms of avoidance/precaution

Question 43

Q: What is the basic reproductive number, R0? Less than 1? Above 1? Aim?

Answer 43

A: Average number of secondary cases from the emergence of a single primary case

If this number is less than 1 it will stutter to extinction and values above 1 is suggestive of epidemic and increase transmission
The main aim is to bring this number down to less than 1.

Question 44

Q: What are the factors that affect the basic reproductive number? (4)

Answer 44

A: • Duration of incubation period
• Peak infectiousess
• How quickly infectiousness decays
• Is acquried immunity important