1st Year
Population and Public Health 1
Public Health
The science and art of preventing disease, prolonging life and promoting health through
organised efforts of society.
Epidemiology
The study of patterns of disease frequency.
Measures of disease frequency
There are two measures of disease frequency:
1. Prevalence
The frequency of a disease in a population at a point in time, hence it is often called point
prevalence.
Point prevalence
=
Number of cases in a defined population at one point in time
Number of persons in a population at the same point in time.
Prevalence is a proportion. It is the only measure of disease occurrence that can be obtained
from cross sectional studies. It measures the burden of disease in a population. Prevalence
measures status : a condition.
2. Incidence
Quantifies the number of new cases of a disease within a specified time interval. Incidence
measures events (a change from a healthy state to a diseased state)
Incidence =
Number of new cases of disease in a given time period
.
Number of disease-free persons at the beginning of that time period
This measure of incidence can be interpreted as the probability, or risk, that an individual will
develop the disease during a specific time period.
Major types of Study
1. Descriptive
a) Ecological  populations
b) Cross-sectional  individuals
2. Analytic
Observational studies – investigator observes who is exposed and
a) Cohort
who develops disease (no intervention)
b) Case control
c) Controlled trials  The investigator allocates the exposure and follow the subjects
(Intervention
for development of disease (randomisation)
studies)
}
Descriptive
Ecological  Use groups or populations rather than individuals. Include geographical
differences and time trends in disease incidence and prevalence. Good for
providing information on exposure, disease and modifying factors they are in
most cases inadequate to establish a casual relationship.
Cross-sectional Studies

Describe the distribution of disease in relation to:
Person  age, sex, race etc
Place  Variation between and within
Time  Variation over time and season
The study is quick and easy. It provides clues leading to hypotheses which can be tested by
analytical studies.
Analytical Study
Observational studies:
a) Cohort: subjects classified according to presence or absence of exposure to factor
and followed for a specific time period to determine the development of
disease. Follow up period of several years.
Good for rare exposures, can examine multiple effects of a single exposure.
Prospective cohort study  Exposure may or may not have occurred but disease has not
occurred yet.
Retrospective cohort study  Investigation initiated after both exposure and disease has
occurred.
b) Case control:
A case group with disease compared with a control group without
disease and the proportion of exposed in each group compared.
Strengths – Quick & cheap. Well-suited for evaluation of diseases with long latent
periods. Optimal for evaluation of rare disease.
Weaknesses – Inefficient for rare exposures; selection difficult and critical. Incidence
rates cannot be calculated.
Intervention Studies:
c) Controlled trials: The investigator allocates the exposure and follows the subject for
development of disease (randomisation)
Standardised Mortality Ratio (SMR)
Is a rate ratio adjusted for the effect of age. It represents the ratio of the number of observed
deaths (O) in a particular population to the number that would be expected (E)
SMR =
Number of observed deaths
.
Number of expected deaths if experienced the
same age specific rates as standard population
Infectious Diseases
Current infection problems:
1. New and emerging infections (HIV, CJD)
2. Old infections that have never gone away (TB, Malaria)
3. Change in geography of infection  Increase in range of tropical disease and travel
4. Infections that are now difficult to treat  Antibiotic resistance
5. Infections in the immuno-compromised
6. Hospital acquired infection.
Sickle Cell and Malaria
There are three lines of evidence suggesting an association between the sickle cell allele and
malaria:
1. Geographical correlations
2. Epidemiological associations
3. Biochemical studies
Commonest Causes of World Death
1. Acute respiratory infections
2. AIDS
3. Diarrhoeal diseases
4. TB
5. Malaria
6. Measles
Whole body nutrition
Many chronic diseases are related to nutrition:
1. Type II diabetes
Basic needs are oxygen, food and
2. CHD
water
3. Cancer
Average requirements
 Intake needs to maintain circulating level or tissue concentration
 Intake associated to absence of disease
 Intake needs to maintain balance
 Intake needs to cure signs of deficiency
 Intake associated with an appropriate biochemical marker of adequacy
Estimated average requirement  EAR
Fundamental importance of body composition as it will dictate:
1. Energy expenditure
2. Response to disease
3. Risk to chronic disease
4. Sporting ability
Changes with ageing
1. Decline in body size
2. Increase in body fat
3. Decline in muscle mass
4. Decrease in liver mass
5. Decline in kidney mass
6. Decline in total body water
These are made even worse with
illness and institutionalisation.
Muscle and fat mass drop.
Downward spiral into malnutrition.
Assessment of body composition
 BMI is a. clinically relevant way of estimating adiposity.
 Weight measurement
BMI = Weight (kg)
Height (m2)
20 – 25  Normal
25 +  FB!!
Laws of thermodynamics
When weight is stable: Energy in = Energy out + Energy stored
Weight gain:
Energy in exceeds energy out.
Increased uptake
Decreased expenditure
Decrease in metabolic rate
Complications of obesity
1. Type II diabetes
2. CHD
3. Cancer
4. Osteoarthritis
5.
6.
7.
8.
Gallstones
Sleep apnoea
Reproductive disorders
Increased pregnancy risk
Estimating intake is very difficult : the obese underestimate the malnourished overestimate.
Macronutrient balance
Auto-regulation
Intake
Alcohol
CHO
Protein
Fat
-
Expenditure
minus
Alcohol
CHO
Protein
Fat
=
equals
Stores
Alcohol
CHO
Protein
Fat
Perfect
Excellent
Excellent
Poor
Fat is not in oxidation hierarchy leads to fat sparing
Population and Public Health 2
Class
Free sugars
Short chain CHO
Starch
Fibre (non-starch
polysaccharides)
Components
Mono & disaccharides
Sugar alcohols
Oligosaccharides
Insulin
Rapidly digestible  amylase
Slowly digestible  amylopectin
Insoluble  Little metabolic effect
Soluble  Metabolic effect
Major role of fat
1. Supply of energy
 Oxidisable energy source
 Major storage form of energy
 Whole tissue
 Adipocyte role in appetite regulation
2. Structures
 Cell membranes
 Structural component of brain tissue and myelin sheath
3. Hormones and prostaglandins
4. Protection
5. Inflammatory response
Essential fatty acids  Linoleic plays a major role in Arachidonic acid and prostaglandin
synthesis.
Transport of lipids
You Need a diagram here.
Saturated fat raises LDL cholesterol
inhibiting its removal and stimulating
its synthesis.
Types of fat  Saturated, polyunsaturated and monounsaturated fatty acids.
Protein Requirements
Constant turnover, therefore a constant need for protein. Body conserves protein in liver.
Protein deficiency
Causes  Failure to meet energy requirements
Catabolic response
Failure in absorption
Excessive protein loss
Results in 
Stunted growth, muscle wasting, infections, wound healing, anaemia,
oedema.
Alcohol
Impossible to store in the body. Some metabolised by alcohol dehydrogenase in stomach.
Liver is main site of metabolism by alcohol dehydrogenase.
Individual Immunity
 Following naturally acquired infection
 Following passive immunisation e.g. maternal antibodies
 Following active immunisation
Public Health Nutrition
There is a strong suggestion that changes in food intake are strongly associated with
alterations in the risk of many diseases.
Ischaemic heart disease is a large problem.
World anomalies
Indian men and women  Far less large bowel cancer
Japanese men  Far more cancer of the oesophagus and stomach
Indian men  Reduced prevalence of lung cancer
USA women (white)  High breast cancer levels
Odds ratio
Disease
+ (cancer)
- (no cancer)
Risk
Factor
+
(smoking)
(non smoking)
Relative risk =
Total
Incidence
a .
(a + b)
c .
(c + d)
a
b
a+b
c
d
c+d
Incidence in exposed .
Incidence in unexposed
=
a / (a + b)
c / (c + d)
Odds ratio =
a/b
c/d
=
axd
bxc
Population Immunity
Why infection control is important:
1. Infectious diseases are common with high morbidity and mortality
2. Lots of money spent on it
3. Money lost by time off work
Control by 
Health protection
Health promotion
Vaccination / medical protection
Contacts / Outbreak investigation
Aseptic techniques and hand washing are exceptionally important.
Health Protection
Clean water, hygiene standards, food standards (production, handling), screen workers (e.g.
health food)
e.g. toxoplasmosis (protozoa) causes mild illness, immune suppression and problems in 1 st
trimester. From cat poop (no rude words mr maslen!), garden, uncooked meat.
Health Promotion
Food handling and preparation in the home.
Pregnant women avoid brie (??) and gardening
Condom use
Avoid mosquito bites
Defined as : The process of enabling people to increase to increase control over and to
improve their health.
Tuberculosis  Kills more adults than any other infectious disease.
Vaccination / Medical Protection
Vaccination and prophylaxis / malaria
Protects individuals and population.
Passive immunisation  Short duration
Active immunisation  Partial protection (some people fail to respond)
Waning levels of protection
Miss out on vaccination
Herd immunity
High levels of immunity in the population protect those who are not immunised e.g. measles
Defined as: The resistance of groups of people to the spread of immunity.
Depends on:
1. Proportion who are immune
2. Frequency of new introductions of infections
3. Degree of mixing between people who are infected and those who are susceptible
4. Transmissibility and duration of infection
Vaccination programme aims:
1. To protect vaccinated individuals
2. To protect non-vaccinated individuals through herd immunity
Example of Rubella
Mild illness but severe effects on foetus
First programme  girls for individual protection
Non-vaccinated pregnant women at high risk
Therefore introduced population vaccination to protect those women by herd immunity.
Meningococcal Disease
Transmitted person to person through droplets of respiratory secretions (close prolonged
contact with carrier)
2 segrogroups B and C >90% of cases
Others include A, Y, W-135, 29E +2.
Symptoms include flu-like illness, stiff neck, dislike of bright lights etc. Illness often progresses
rapidly (within hours)
Meningococcal disease is the most common infectious cause of death in children and young
people up to 20 years. Number 1 killer in children aged 1 – 5 years.
Risk factors  Age and sex (Male > female)
Season
Contact with a case
Following influenza A
Passive smoking
Control by  Antibody prophylaxis in close contacts
Vaccination of close contacts
Population vaccination
No vaccine for group B disease.
Septicaemia
Most severe and life threatening. Overall fatality rate ~ 10%
May cause brain damage, seizures, deafness.
Contact / Outbreak Investigation
Contact tracing (TB, STI)
Identify and control sources
Reducing the risk of transmission:
Quarantine, advice
Investigate contacts and vaccinate +/- treat
Surveillance  ongoing systematic collection, collation, analysis and interpretation of data.
And the dissemination of information to those who need to know in order that
action can be taken.
Surveillance is for:
Detecting epidemic / outbreak
Monitoring trends
Evaluating intervention
Future planning
Vitamins & Minerals
Vitamin C deficiency  scurvy.
Main role is for collagen synthesis, immune function, iron absorption
Vitamin D  Rickets and osteomalacia
Minerals
Electrolytes (Na)  blood pressure
Ca  Bone health
Iron  Oxygen transfer
Zinc  Stabilises DNA and RNA
Iron deficiency and iron deficient anaemia gives a state of negative iron balance. Anaemia
when haemoglobin levels start to drop.
Most common nutritional deficiency in the world  iron deficiency.
Vitamins and minerals are essential for a wide variety of body functions.
Deficiency of one can affect many systems.