Lectures 3&4 - The importance of evidence in the practice of medicine part 2 & Global patterns of disease part 1

Question 1

what is epidemiology?

Answer 1

ability to quantify occurrence of disease in populations

Question 2

what is prevalence?

Answer 2

• frequency of disease in a population at a point in time
• only measure of disease occurrence that can be obtained from cross sectional studies
• measures burden of disease in population (which can be compared between populations)

Question 3

how is prevalence calculated?

Answer 3

of cases in population / # of people in population

Question 4

what is incidence?

Answer 4

• # of new cases of a disease within a specified time interval
• probability that an individual will develop the disease during a specific time period

Question 5

what is the difference between prevalence and incidence?

Answer 5

PREVALENCE = all cases

• dependent on incidence and duration of disease
• individuals only leave “pool” of prevalent cases when they recover/die

INCIDENCE = new cases

Question 6

how is incidence estimated?

Answer 6

• define the time period under question
• define the denominator = total population at risk
• define a true case by having an accurate test (easier for infections which have a short time period rather than chronic infections)

Question 7

what happens to prevalence if incidence stays the same?

Answer 7

prevalence can go up if you are keeping people with the disease alive

Question 8

what is mortality?

Answer 8

the number of deaths from a specific disease in a given time period

Question 9

how is mortality calculated?

Answer 9

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

Question 10

describe the relationship between mortality, incidence and prevalence

Answer 10

if mortality = incidence the epidemic is stable

if mortality is reduced (people are kept alive for longer):

• incidence may go up as people are more able to transmit diseases to other people
• prevalence may go up as there are more cases and fewer people dying

Question 11

what is morbidity?

Answer 11

the number of cases of ill health, complications or side effects attributed to a particular condition over a period of time

Question 12

what is the difference between mortality and morbidity?

Answer 12

MORTALITY = # of people who died 
MORBIDITY = state of being diseased/unhealthy

Question 13

how is morbidity measured?

Answer 13

• scores/predicted morbidity assigned to ill patients with systems such as APACHE II, GCS, PIM2, SOFA
• these help decide the treatment that should be given
• these are useful in comparing 2 sets of patients or different time points in hospital

Question 14

how is mortality measured?

Answer 14

• rates are normally expressed as # of deaths/1000 individuals/year

Question 15

which country has the highest death rate and what is it?

Answer 15

swaziland - 30.83 deaths/1000 individuals/year

Question 16

what are the leading causes of death?

Answer 16

• heart diseases
• cerebro-vascular disease
• respiratory infections
• HIV/AIDS
• COPD

in 3rd world countries 58% of the mortality reported was due to malnutrition

Question 17

what are the 6 leading causes of infectious disease?

Answer 17

• Lower respiratory infections
• HIV/AIDS
• Diarrhoeal diseases
• TB
• Malaria
• Measles

Look How Dey Teach (Muslim Medics)

Question 18

what does age standardised death rate mean?

Answer 18

age adjustment which allows populations to be compared when the age profiles are quite different

Question 19

why are age standardised death rates important?

Answer 19

• measuring how many people die each year and why is important in assessing the effectiveness of a country’s health system
• can help determine whether health actions are being correctly focused
• almost 15% of deaths from infectious disease are in children <5
• most of these preventable deaths in children occur in LICs and MICs

Question 20

describe the history of AIDS

Answer 20

• 1st case was David Carr in 1959 who was found to have PCP and CMV infections, never previously reported in adults
• in 1980 a 33 year old man was admitted with PCP
• in 1981 5 gay men had similar illnesses
• GRID = “Gay Related Immune Disease”
• growth of the epidemic in the US from 5 cases in 1980 to 79,000 cases in 1993
• 1.3m living with HIV by 2006
• case control studies conducted and all exposures questioned (sexual, medical, chemicals, pets, drugs etc)
• cases had twice as many sexual partners, and a greater history of syphilis
• no association with “poppers” - drug taken by many gay men
• disease was seen amongst young gay men, related to sexual contact
• disease was also seen in injection drug users and transfusion recipients
• 10 women also had the disease - all had sex with bisexuals/drug users
• test for virus arose in 1984 but there is still no treatment
• antiretroviral therapy (ARTs) became available in mid 90s

Question 21

describe AIDS now

Answer 21

• global disease
• transmission through bodily fluids
• 90% of disease in developing countries

Question 22

what are the WHO aims for HIV/AIDS?

Answer 22

• no new infections
• no new babies infected
• no more HIV related deaths globally

Question 23

what is a case control study?

Answer 23

a retrospective study that starts with an outcome and traces back to investigate exposures, comparing individuals with and without the outcome

Question 24

how is a case control study designed?

Answer 24

1) identify the cases and the controls
2) look back in time to understand which subjects has specific exposures, comparing the frequency of the exposure in the case group to the control group

Question 25

what is the aim of a case control study?

Answer 25

to determine whether an exposure is associated with an outcome

Question 26

what are the advantages of a case control study?

Answer 26

• cheap
• quick
• good for investigating outbreaks of infectious disease

Question 27

describe the successes of the response to the AIDS epidemic

Answer 27

• broad access to ARTs for HIV in poor countries
• 10-fold growth of access to therapy for HIV/AIDS in Africa from 2002-2007
• declines in HIV prevalence in pregnant women
• knowledge of how to eliminate mother -> baby transmission as mother is given ART before delivery
• increased # of effective HIV prevention methods (e.g. safer injection practices, condoms)

Question 28

describe the challenges of the response to the AIDS epidemic

Answer 28

• for every 1 person on HIV therapy today, 5 are newly infected
• HIV infection rates have only been decreased to a certain level
• many people choose not to be tested
• preventing the 3,550 HIV infections that were diagnosed in the UK in 2008 would have reduced HIV-related costs by £1.1b

Question 29

outline the global status of HIV

Answer 29

• only 45% of all HIV infected women have access to treatment to prevent transmission to babies
• less than 40% of people with HIV know their status
• more than 4m people increase in HIV over the past year (10 fold increase over past 5 years)
• 6.7m people need ART but only 2.9m are on ART

Question 30

what are the key measures of disease in the population?

Answer 30

• case
• prevalence
• incidence

Question 31

outline the UK status of HIV

Answer 31

• incidence of HIV is rising in the UK
• # of deaths from AIDS has declined due to improved treatment
• duration of disease is therefore increasing therefore prevalence of HIV has increased