Surveillance & Morbidity Flashcards
3 Objectives of Descriptive epidemiology
- Permit evaluation of trends in disease (monitor disease, identify new disease) and compare across subgroups
- Provude sound basis for provision and evaluation of health services (planning)
- Identify problems to be studied by further analytic (generate hypothesis)
Surveillance
Ongoing systematic collection, analysis, and interpretiation of health data, essential to the planning, implementation and evaluation of public health practice, closely integrated with the timely dissemination of these data to those who need to know.
Most descriptive data comes from surveillance systems
Like healthy people objectives or NHANES surveys
Passive Surveilllance
- Disease reporting mandated by goverment or health authority (HIV, syphilis)
- Completeness and quality of data depend on staff
- they take take the role without funds or payment
- Low quality, its Affected by underreporting and lack of completeness
Active surveillance
- Staff recruited to carry out a surveillance program specifally designed for disease
- Field visits to identify incidence may involve interviews to medical staff, pt and records
- More accurate, individuals employed and trained just for this
- More difficult initially and more expensive
Counts
Measures of disease frequency
Number of cases of disease (outcome of interest)
1. Simplest & most frequently used quantitative measure in epi
3. Very informative when outcome of interest is rare
4. Presence of any disease is alona a critical observation
Lack of denominator avoid estimate magnitude
No of students received A in epi
No of traffic fatalities in Dallas
No of persons with influenza in UTSW in January
Proportions
Measures of disease frequency
Measure that states the count relative to the size of the group from which the count was calculated.
Used to undestand magnitude of problem
Have numerator and denominator
12 students out of 23 received A in EPI
3 traffic fatalities out of 500,000 drivers in Dallas
600 with influenza amoung 700 in UTSW in Jan
Can be ratio 12/23, 3/500000, 600/700
Can be percentage 52%, 0.0006%, 0.012%
Magnitude of problem 10 students failed if 20 are in the class 50% failed but if 200 only 5% failed.
Ratios
Measures of disease frequency
Ratio is a fraction, consist in numerator and a denominator but no specified relationship between them
No of male cases (30) = 30
No of female cases (50)= 50
30:50 male to female ratio
Rate
Measures of disease frequency
Proportion or ratio that consists of numerator and a denominator where denominator includes time
Event frequency (numerator)/population size*time (denominator)
No of heart failure = 1018
Person years follow up = 390,009
Rate of HF per 100,000 py = 1018/390,009 x 100,000 = 261 per 100k
Point Prevalence
Existing cases of disease in a population at some designated point in time
Formula:
NoExistingCases/No persons in population
At a certain point in time
e.g on Jan 25 2018 16 of 61 kids were sick in Dallas
Helps with burden of disease and allocate health resources and intvtns
Rare conditions have high prevalence if duration is long,
Common health conditions low prevalence if duration short
Period prevalence
How many people have had a disease during a certain time period
Formula:
NoExistingCases/No persons in population
During time period
e.g: During 2015 to 2016 20 of 61 people was sick
Incidence proportion or Cummulative Incidence
Number of new first ever cases of a disease or health condition over a time period.
NoNewCases/TotalPopulationatRisk
during a certian point in time (NO PERSON TIME)
Excludes those who already have the disease or are not capable of developing like women without ovaries and men cannot develop ovarian cancer
Incidence Density or Incidence Rate
Number of new cases of disease arise during person time of observation
NoNewCases/TotalPopulationatRisk
during a period of time (PERSON TIME)
Denominator is a dynamic population
Person time steps
1. New cases * PersonYears
2. Population at risk * PersonYears (Substract new cases and withdrawals)
3. WithdrawalsParticipation * PersonYears
4. New cases count / TotalPersonYears x 1000
Dynamic population
Continually changing
Allows both addition of new members and loss of previously entered
E.g DISCHARGED PATIENTS, DEATHS, ADMISSIONS
Used in incidence or density rate
Fixed population
Individuals at some point in time followed for a given period of detection
No entires or exits.
Used on cumulative incidence or incidence proportion
Relationship of Incidence and prevalence
Prevalence = Incidence * Duration of disease
P = ID
