Download Folic Acid in Prevention of Neural Tube Defects

Natural History of Disease
Ahmed Mandil
Prof of Epidemiology
Family & Community Medicine Dept
King Saud University
Headlines





Definitions
Induction, incubation, latency
CHD Natural history of disease
Lead time
Survival time
May 24, 2017
Natural History of Disease
2
Phenomenon of disease:
Natural history 1
• Disease is a process that unfolds over
time
• Natural history – sequence of
developments from earliest pathological
change to resolution of disease or death
May 24, 2017
Natural History of Disease
3
Phenomenon of disease:
Natural history 2
• Induction – time to disease initiation
• Incubation – time to symptoms
(infectious disease)
• Latency – time to detection (for noninfectious disease) or to infectiousness
May 24, 2017
Natural History of Disease
4
Phenomenon of disease:
Natural history 3
• Induction – time to disease initiation
• Incubation – time to symptoms (infectious
disease)
• Latency – time to detection (for noninfectious disease) or to infectiousness
May 24, 2017
Natural History of Disease
5
Phenomenon of disease:
Natural history 4
• Induction – time to disease initiation
• Incubation – time to symptoms (infectious
disease)
• Latency – time to detection (for noninfectious disease) or to infectiousness
May 24, 2017
Natural History of Disease
6
Natural History of Disease
Detectable subclinical disease
Susceptible
Host
Subclinical
Disease
Point of
Exposure
Clinical
Disease
Diagnosis
sought
Outcome:
Stage of
Recovery,
Complications,
Disability, or
Death
Onset of
symptoms
Screening
24 May 2017
Screening
7
Natural history is
central to screening
Detectable,
preclinical
Pre-detectable
Age:
35
45
Possible detection
via screening
May 24, 2017
Disability
or death
Clinical
55
65
75
Clinical
detection
Natural History of Disease
8
Potential Methodological Issues



Selection bias:
 Referral (voluntary) bias: volunteers being healthier,
more compliant
 Length-biased sampling (prognostic selection): does
screening selectively detect cases with better
prognosis ?
Lead-time bias: how earlier can diagnosis be made if
the disease is detected by screening compared with
usual timing of diagnosis if screening was NOT carried
out ?
Over-diagnosis bias: resulting in misclassification
24 May 2017
Screening
9
Survival time after diagnosis –
lead time 1
Detectable,
preclinical
Pre-detectable
Age:
35
45
Disability
or death
Clinical
55
65
75
Lead time
Possible detection
via screening
May 24, 2017
Clinical
detection
Natural History of Disease
10
Survival time must increase >
lead time 2
Clinical
diagnosis &
treatment
Undetected
(no screening)
Pre-detectable
Disability
or death
Survival time after diagnosis
Early detect,
diagnosis, &
treatment
Pre-detectable
Monitoring
for recurrence
?
Lead time
Age:
35
May 24, 2017
45
55
Natural History of Disease
65
75
11
Slowly progressing diseases are
easier to detect by screening
Clinical
diagnosis,
treatment
Predetectable
Disability
or death
Survival time after diagnosis
Clinical
diagnosis &
treatment
Detectable,
pre-clinical
Pre-detectable
Disability
or death
Survival time after diagnosis
Age:
35
May 24, 2017
45
55
65
Natural History of Disease
75
12
Natural history of
coronary heart disease 1
“Spontaneous
atherosclerosis”
Chronic
minimal injury
(blood flow,
CHL, smoking,
infection?)
(youth?)
May 24, 2017
Fibrointimal
lesion
“Lipid lesion”
Accumulation of
lipids and
monocytes,
toxic products,
platelet
adhesion
(adolescence)
Plaque growth,
occlusion
Migration &
Disruption
proliferation of
thrombi
smooth
muscle cells
(adulthood)
(adulthood)
Natural History of Disease
13
Natural history of
coronary heart disease 2
“Spontaneous
atherosclerosis”
Chronic
minimal injury
(blood flow,
CHL, smoking,
infection?)
(youth?)
May 24, 2017
Fibrointimal
lesion
“Lipid lesion”
Accumulation of
lipids and
monocytes,
toxic products,
platelet
adhesion
(adolescence)
Plaque growth,
occlusion
Migration &
Disruption
proliferation of
thrombi
smooth
muscle cells
(adulthood)
(adulthood)
Natural History of Disease
14
Natural history of
coronary heart disease 3
“Spontaneous
atherosclerosis”
Chronic
minimal injury
(blood flow,
CHL, smoking,
infection?)
(youth?)
May 24, 2017
Fibrointimal
lesion
“Lipid lesion”
Accumulation of
lipids and
monocytes,
toxic products,
platelet
adhesion
(adolescence)
Plaque growth,
occlusion
Migration &
Disruption
proliferation of
thrombi
smooth
muscle cells
(adulthood)
(adulthood)
Natural History of Disease
15
References




Raffle A, Gray M. Screening: Evidence and
practice. Oxford: Oxford University Press, 2007
Gordis L. Epidemiology. Chapters 5, 18. 2009
Schoenbach VJ. Natural history of disease and
population screening. Gillings School of Public
Health. University of North Carolina – ChapelHill, USA.
Weissfeld JL. Screening and early detection
May 24, 2017
Natural History of Disease
16
Thank you for your kind attention
May 24, 2017
Natural History of Disease
17