Epidemiological Surveillance Approach to Population Health

epidemiology

• study of the distribution and determinants of disease frequency in human populations

• application of this knowledge to control health problems

john snow

father of modern epidemiology

environmental theory

• populations based approach to improve environmental conditions

• state of villagers suffering due to unjust social policies

• health is linked to the environment

• importance of collaborators and resources

key objectives of epidemiology

• study the natural course of disease from onset to resolution

• determine the extent of disease in a population

• identify patterns and trends in disease occurrence

• identify the causes of disease

• evaluate the effectiveness of measures that prevent and treat disease

key assumptions of epidemiology

• human disease does not occur at random

• there are factors/determinants which can increase the likelihood of disease

• the factors/determinants can be identified by systematic investigations

epidemiologic triad

• conceptual framework used in epidemiology to understand the interaction of factors that contribute to the occurrence and spread of diseases

• consists of:

  • host

  • agent

  • environment

host

• individual or population susceptible to the disease

• examples

  • host genetics

  • stage of infection

  • antiretroviral therapy

  • reproductive tract infection

  • cervical ectopy

  • male circumcension

  • contraception

  • menstruation and pregnancy

agent

• biological, chemical, or physical factor that causes the disease

• examples

  • HIV subtype

  • phenotypic differences

  • genotypic differences

  • antiretroviral drug resistance

environment

• external factors that facilitate or hinder the interaction between the agent and the host

• examples

  • social norms

  • avg rate of sex-partner change

  • local prevalence/probability of exposure

  • social and economic determinants or risk behavior

RMS

daily or weekly counts of total mortality by age, sex, date of death, place of death, and place of usual residence

excess mortality

degree to which currently measured mortality exceeds historically established levels

surveillance

• ongoing systematic collection, analysis, interpretation, and dissemination of data regarding a health event for use in public health action to reduce morbidity and mortality to improve health

• ex: characterizing patterns of disease, detecting epidemics, further investigation, research, disease control program, detecting priorities, and evaluation

types of surveillance

• passive

• active

• serovurveillance

• sentinel

• syndromic surveillance

passive surveillance

• routine reporting of health data

• ex: notifiable diseases, disease registries (birth, deaths, cancer, chronic diseases)

active surveillance

• actively seeking out health info; active case finding

• ex: outbreaks, serosurveillance, health surveys

• complete and better quality

• resource intensive

serovurveillance

• type of active surveillance

• testing blood markers to get an estimate of antibodies against infectious diseases

sentinel surveillance

• selective institutions/groups to provide health data on specific diseases

• helpful for monitoring diseases, trends, detect outbreaks

• not good to detect outside sites/groups, rare conditions

syndromic surveillance

• monitoring non specific syndromes

• ex: fever, respiratory issues, GI illness, med purchases, absenteeism

• helps with early detection of cluster illness

• relies on automated systems

rumor surveillance

• unofficial sources of info

• ex: blogs, media, hearsay, socials

• can help alert authorities and early detection

what makes a good surveillance system?

• simplicity

• flexibility

• quality

• acceptability

• sensitivity and PPV

• validity

• representativeness

• timeliness

• stability

• evaluation

• information for action

outbreaks

occurrence of cases of an illness clearly in excess of what is normally expected in a small limited region

epidemic

outbreak spread to other geographical regions

endemic

usual occurrence in a geographic area

pandemic

worldwide epidemic

observation bias

occurs when a researcher's expectations, beliefs, or personal preferences unintentionally influence what they perceive or record during a study

recall bias

participants do not accurately remember past events or experiences, leading to inaccurate reporting

interviewer bias

• unconscious or conscious prejudice that an interviewer has towards a candidate, which influences their judgment and decision-making

• ex: how you word a question may come across different to people

confounding variable

• presence of a 3rd factor that can affect the observed relationship between an exposure and a disease outcome

• must be associated with the outcome independently of exposure

• ex: temp, age, time, exercise/diet

independent variables

suspected cause or risk factor; also known as the exposure

dependent variables

outcome or disease being studied

measures of occurrence

• ways to describe the distribution of outcome

• examples

  • prevalence total

  • incidence rate

  • cumulative incidence

prevalence total

frequency of disease at a given point in time

prevalence formula

# of people with disease at a point in time/total # of people in the population at that point int time

incidence

frequency of disease that develops over a period of time

incidence rate formula

# of new cases of disease during observation period/total observation time at risk

cumulative incidence

proportion of population/at risk group that develop the outcome of interest during a time interval

cumulative incidence formula

# of new cases of disease (outcome)/# of people in source population at risk

measures of association

• describe association between outcome and its determinants

• examples

  • proportion

  • odds

proportion

• part/whole expressed as a percentage

• range 0 to 1

odds

• a ratio of the probability of occurrence of an event to that of nonoccurrence

• part/non part

• range is 0 to infinity