DISEASE EPIDEMIOLOGY – THE ABSOLUTE BASICS
CANCERS
OVERVIEW:
Data from deaths and registrations – true incidence unknown. Registrations may increase
with better diagnosis including screening.
In UK:


Stomach and lung: going down
Breast and bowel – registration going up, deaths going down
[nb both screening but drop in mortality too early to be wholly screening effect]

Melanoma – deaths and registrations going up for Eng
But different pattern in some Registries e.g. Oxford, Scotland
BREAST CANCER
Time: Decline in deaths over past 10 years, registrations up.
Place: UK highest death rate in Europe, no variation within UK
Person:
Age: Rare but not unknown in women under 40
Sex: Males can get it but very rare
Social Class: Reverse social class gradient – death rate in soc cl I > Soc cl
V
Ethnic: Less common in social groups who start their families early (e.g.
Banglasdeshi?). Rare in ethnic Chinese; common in Ashkenzi Jews.
Occup: No occupational association
Familial / genetic: BrCa1 gene confers 80% lifetime risk, but this
accounts for only a small proportion of population cases
Lifestyle: Associated with late age at first pregnancy
Other: Drop in mortality in UK occurred too soon to attribute to screening –
this may be a Tamoxifen effect but also a cohort effect.
BOWEL CANCER [think fibre]
Time: Registrations up, death down in UK over past 20 years
Place: No variation in registrations within UK but survival after diagnosis lower
in North. Very rare in some countries e.g. Nigeria
Person:
Age: Uncommon in people under 40, increasing thereafter
Sex: Similar incidence in males and females
Soc Cl: Survival after diagnosis worse in Soc cl V
Ethnic:
Occup: No occupational association
Lifestyle: Less common in societies with high fibre diet
Familial: Some genetic forms e.g. with polyposis coli or non-polyposis
hereditary colon cancer (NPHCC)
Other: Screening reduces mortality by 30%; NHS pilot of screening successful.
LUNG CANCER [think smoking]
Different cell types – commonest is squamous cell.
Time: Registrations and deaths declining in UK
Place: Death rates higher in deprived areas of UK. Very high rates in Finland,
low rates in Muslim countries
Person:
Age: Uncommon in people under 40, increases in incidence thereafter
Sex: Male death rate exceeds female, but gap narrowing
Soc Cl: Commoner in Soc Cl V than I
Ethnic: Rare in communities which do not smoke
Occup: Commoner in occupations with high proportion of smokers e.g.
publicans and soldiers
Lifestyle: Very strong association with smoking, some association with
environmental tobacco smoke (passive smoking)
Familial: No familial association except through smoking habit
CANCER OF CERVIX [think sexually transmitted]
Time: Decline in registrations and death in UK over past 20 years
Place: Deaths higher in inner city in UK especially London; globally, death rates
are higher in third world e.g. Sri Lanka
Person:
Age: Dysplasia is common in people in their 20s but invasive cancer rare
under 40 years; half of all deaths in people over 65
Sex: Only affects females
Ethnic: ??
Soc Cl: Commoner in soc cl V than I
Occup: Said to be commoner in sex workers (prostitutes)
Lifestyle: Commoner in people with low age at first sexual intercourse
and many sexual partners
Familial: No familial tendency
Other: Associated with human papilloma virus infection: vaccine now available.
MELANOMA [think sunburn]
Time: Deaths and registrations increasing in UK over past 20 years; (but complex
patterns in some Registries e.g. increase had stopped Oxford, perhaps Scotland. Peak incidence in
people born before 1950)
Place: Commoner in South West of England, common among white people in
Australia
Person:
Age: Occurs from age 20 on
Sex: Deaths commoner in men than women; registrations commoner in
women than men [with regional variation]
Soc Cl: Commoner in Social class I than V i.e. reverse soc cl gradient
Ethnic: Less common in people with black or coloured skin
Occup: Commoner in outdoor workers e.g. farming and forestry
Lifestyle: In case control studies, commoner in people who have been
sunburned, also users of sunbeds.
Familial: Some familial forms.
NON CANCER
DIABETES MELLITUS [think obesity for Type II diabetes]
Definitions: Two types – insulin dependent and non-insulin dependent
(NIDDM), now called Type I and Type II because some people with the late
onset ‘NIDDM’ actually need insulin to control their disease.
Type I – body doesn’t produce insulin
Type II – insulin produced, receptor failure
Time: Both types increasing in incidence in UK as judged by hospital data and
some research surveys
Place: Commoner in UK in small areas with high Indian population e.g. West
London
Internationally very common in some communities e.g. Pima Indians
Person:
Age: Type I onset is in childhood, declining incidence thereafter; Type II
onset is in adults usually aged 40 or more but can be younger
Sex: Similar incidence in male and female
Soc Cl: Type II is commoner in Social Class V than I; Type I similar in all
Social Class
Ethnic: Commoner in Indian communities in UK
Occup: No association with occupation
Lifestyle: Strong association of Type II with obesity
Familial: Family tendency in Type I (plus some very rare single gene
types)
SCHIZOPHRENIA [think drift – i.e what the disease does to your life]
Time: Thought to be declining in UK since 1960s based on health service data
but no accurate surveys
Place: Commoner in inner cities in UK. Internationally similar incidence in all
countries if standard criteria used, but e.g. in old USSR diagnosed frequently for
political reasons
Person:
Age: Onset in teenage years, declining incidence after 30
Sex: Somewhat commoner in male than female
Soc Cl: Commoner in Social class V than I [nb drift]
Ethnic: Diagnosed more commonly in Black Caribbeans but this may be
artefact
Occup: No occupational association except difficult to work with active
schizophrenia; commoner among homeless people and prison inmates
Lifestyle: Commoner among drug users including cannabis and IVDU
Familial: Commoner in first degree relatives of cases
DEMENTIA
Definitions: Two types – Alzheimers and vascular. Vascular epidemiology likely
to match smoking
Time: Increasing prevalence in UK (more old people) but no surveys to show if
age-specific incidence is increasing
Place: Commoner where there are more old people e.g. Brighton but no evidence
on spatial variation in age-sepcific incidence
Person:
Age: Occasional onset in people under 65 (pre-senile); increasing
incidence from age 65 on
Sex: Similar age-specific incidence in male and female
Soc Cl: Vascular dementia is commoner in social class V than I [NB
smoking and vascular disease]
Ethnic: no data yet – in the UK ethnic minorities tend to be younger than
the white population
Occup: No occupational association
Lifestyle: Vascular dementia commoner in smokers
Familial: Genetic form of Alzheimer’s confer high risk but accounts for
small proportion of population cases
SUICIDE
Definitions: Coroners verdict not medical opinion. Combine suicide with
‘undetermined’ to track trends.
Time: Strong decline in 1960s, attributed to switch from coal gas. Recent increase
in young males in UK now tailing off.
Place: Suicide rate high in inner London. High in Sweden and Hungary; low in
Catholic countries e.g. Italy, Spain
Person:
Age: Suicide rate higher in old (over 50) than young (under 35). Very rare
in children
Sex: Commoner in male than female
Soc Cl: Commoner in social class V and than I
Ethnic: in Black Americans suicide commoner in young than old
Other: Strong association with any severe mental illness i.e. depression
AND schizophrenia, obsessive disorder etc
Commoner among homeless and single, widowed, divorced; area
measures of 'social fragmentation'
CORONARY HEART DISEASE
Time: There has been a steep (30%) decline in deaths in England over past
20years. Incidence can only be tracked by special surveys but probably also
declining
Place: Death rate high in Glasgow, Tyneside, Merseyside and South Wales; low in
Surrey and south of England. UK rates higher than rest of Europe
Person:
Age: CHD is detectable in teenagers (autopsy after accidental death) but
symptoms uncommon under 40; incidence increases thereafter
Sex: Commoner in male than female
Soc Cl: Commoner in social class V than I
Ethnic – rarer in non-smoking ethnic communities
Occup: No occupational association except through smoking habit.
Famous study in 1960s (Jerry Morris) showed commoner in bus drivers
(who sit) than conductors (who move about)
Lifestyle: Strong association with smoking, obesity, sedentary lifestyle,
psychosocial stress etc etc
Familial: Strong familial tendency
STROKE
For exam purposes regard as same as CHD EXCEPT
1. Ethnic – common in US blacks, especially southern USA - the ‘stroke belt’
of Alabama, Louisiana etc
2. remember the association with high blood pressure
ASTHMA
Time: Deaths declining in UK. Surveys showed increase in prevalence and/ or
severity during the 1980s but recent decline in children.
Place: no clear spatial pattern within the UK. Specifically, not more common
near large road such as the M25.
Person:
Age: Onset is in childhood, prevalence decreases after teenage years (i.e.
some children grow out of it)
Sex: Somewhat commoner in boys than girls
Soc Cl: Wheeze is commoner in children from soc class V families than
soc class I
Ethnic - ?
Occup: Occupational asthma in dusty industries – notifiable disease
Lifestyle: Commoner in children of smoking households
Familial: Atopy (eczema and asthma) runs in families
Other: Case control studies (David Strachan) suggest early exposure to allergens
reduces risk so less common in households with many children
CHRONIC BRONCHITIS
Time: Deaths declining in males, increasing in females in UK, no data on
incidence
Place: Death rate higher in north of Eng than south
Person:
Age: Uncommon in people under 40, increases in incidence thereafter
Sex: Commoner in male than female but gap narrowing in UK [nb
smoking]
Ethnic ? rare in communities which don’t smoke
Occup: Association with some occupations e.g. coal mining
Lifestyle: Strong association with smoking
CARIES
SUDDEN INFANT DEATH
Both strongly associated with deprivation – work it out from there!
LIFESTYLES
Overview:
Smoking, kCal, fat intake all declining in Eng since 1960s but obesity (BMI > 30) up in
last 10 years; alcohol increasing since 1970
SMOKING
Time: Declining in England since 1960s
Place: Higher rates in Scotland than England. Within Europe, English rates lower
than most European countries e.g. France, Greece etc
Person:
Age:
‘Onset’ in 11 year olds. Prevalence peaks in 30years olds, then declines
Sex: More males smoke than females except in teenage years
Soc Cl: Soc Cl V > Soc cl I, but smokers are a minority at all ages in all
social classes
Ethnic: Smoking rare among Muslim communities; also Very few
Chinese women smoke (unlike their menfolk)
Occup: High proportion of smokers in some occupations e.g. publicans,
soldiers
Lifestyle: Strong association with high alcohol intake
ALCOHOL
Definitions: Need to define unhealthy level of alcohol e.g. average of more than
21 / 14 units per week, or ‘binge’ – more than 8 / 6 units on one occasion.
Information every other year since 1974 from General Household Survey (self
report)
Recent focus on peak (binge) rather than average
Time: Mean intake per head of population increasing in Eng
Place: Proportion of young men drinking more than 20 units per week higher in
north of Eng
Person:
Age:
Sex:
Social Class V and I similar intake but different type – beer vs wine
Ethnic: Muslim communities drink little
Occupation: strong association with some occupations e.g. publicans
Lifestyle: High alcohol intake associated with smoking
SEXUAL BEHAVIOUR
All data from sexual health and lifestyle surveys 1991 and 2001 which only included
15 – 44 yr olds
60% of men, 46% of women have 5 or more partners in a lifetime
Median age at first intercourse: 17 for males and females
Mean number of lifetime partners = 12 in London, 8 elsewhere
Homosexual experience: 10% of Londoners, 5% elsewhere
30% of non-manual classes have first intercourse aged <16yrs, 20% for manual
classes.
Johnson AM et al Sexual behaviour in Britain Lancet 2001; 358: 1835 - 42