Exam 1 Flashcards
Epidemiology
the diagnostic discipline of public health
study of the distribution and the determinants (risk factors) of disease and mortality in the population
Quantifying a Disease
1) Define the disease
2) Measure disease frequency:
a) count the number of individuals affected (numerator)
b) determine the size of the population from which the cases arose (denominator)
c) account for the passage of time
Basic types of incidence rates
1) Cumulative Incidence
2) Incidence rate (aka incidence density: person-time incidence rate)
Incidence
the number of new cases per unit population, during a stated period of time
the rate of development of a disease in a population over a specified period of time
contains the following elements:
a) numerator - number of new cases
b) denominator - population at risk
c) rate base or multiplier
d) time - period during which cases accrued
Population at risk (PAR)
the denominator for incidence rates
are AT RISK of contracting the disease
are DISEASE-FREE at the start of the specified time period
exclude individuals NOT AT RISK in the population from the denominator - important with lifelong diseases and infectious diseases that confer immunity
among large populations (ex. US incidence rates), denominator is based on average population
Rate Base
also known as multiplier
rate base - per 100, 1000, or 100000 (to power of 10)
purpose: the reported rate is expressed as a number equal to or greater than 1
Calculate cumulative incidence of colon cancer among this study population:
60 cases of colon cancer were reported in 5 year study of 311 study subjects, colon cancer-free at start of study
Cumulative incidence rate = number of new cases / population at risk
60/311 = 0.1929
19.3 cases per 100 over 5 years
Calculate cumulative incidence rate for ovarian cancer:
# of new cases = 1085 population at risk = 37105 time period = 8 years
incidence rate = 1085 / 37105 = 0.02924
- 02924 / 8 = 0.003655
- 003655 x 100,000 = 365.5 cases per 100,000 women per year
Cumulative incidence rate
represents a population’s average risk of developing that disease during the time/period of observation
Incidence Rate
also known as incidence density
what to do when members of a population or study group are under observation for different lengths of time
Incidence density equation
Incidence density = # of new cases during the time period / total person-time of observation
If measured in years:
Incidence density = # of new cases during the time period / total person-years of observation
What is the incidence rate of colon cancer among this study population per 100 person-years?
60 cases of colon cancer were reported in 5 year study of 311 study subjects. 10 subjects developed colon cancer and 40 dropped out of study after one year, 35 new cases were reported at end of year two; no cases, but 4 subjects dropped out at end of year three, 10 new cases and 12 subjects dropped out at end of year four, and 5 new cases were reported at end of year 5.
Incidence rate of colon cancer is: 60 cases per 1220 person years
Incidence per 100 person-years: (60/1220) x 100 = 4.9 cases per 100 person years
Advantages of incidence rate over cumulative incidence
advantages in follow up studies:
1) allow for subject losses due to withdrawals, deaths or other reasons
2) accommodates subjects entering a study at different times
Applications of incidence data
1) helps in research on the etiology/causality of disease
2) estimates the risk of developing a disease
Attack Rate (AR)
a cumulative incidence rate used when the nature of the disease or condition is such that a population is observed for a short period of time
alternative form of incidence rate
used for diseases observed in a population for a short time period
with acute infectious disease outbreaks, the population-at-risk increases greatly over a short period of time
ex) salmonella gastroenteritis outbreak
Prevalence
the number of cases (new and existing) of a disease or health condition in a population at or during some designated time
provides an indication of the extent of a health problem BUT is NOT a measure of risk
Point prevalence equation
Point prevalence = number of cases / total number in the group at point in time
Period prevalence
Period prevalence = number of cases of disease during a time period
average population at mid-point
cases are counted even if they die, migrate, or recur
Uses of prevalence
1) describing the burden of a health problem in a population
2) determining allocation of health resources such as facilities and personnel
Interrelationship between Prevalence and Incidence
the prevalence (P) of a disease is proportional to the incidence rate (I) times the duration (D) of a disease
Incidence and Prevalence
if duration of disease is short and incidence is high, prevalence becomes similar to incidence
short duration: cases recover rapidly or are fatal (ex. common cold, flu, ebola)
An epidemiologist conducts a survey of Sargentitis Disease in a population.
The prevalence of Sargentitis
among women is 40 per 1,000 and
among men is 20 per 1,000.
Assuming the data is age-adjusted,
is it correct to assume that women have twice the risk of Sargentitis compared with men?
No, there could be a lot more women in the total population compared to men
Changing Patterns of Mortality
until the 20th century the major causes of death in all parts of the world combined were infectious diseases
in the 20th century, control of infectious diseases is paralleled by the emergence of chronic diseases as major causes of mortality
Characteristics of Infectious Diseases
relatively short latency period from exposure to disease
Characteristics of Chronic Diseases
long latency period, 10-20+ years
the length of latency period impacts public health approaches to reduce disease rates within a population
health care and public health care systems need to adapt
Risk factor
a characteristic or agent whose presence increases the probability of occurrence of a disease
Social determinants of a health fact file
fact file: social determinants of health
poverty, social exclusion, poor housing, and poor health systems are among the main social causes of ill health
Objectives of Epidemiology
1) the extent of disease in a population
2) identify patterns and trends in disease
3) identify causes/risk factors of disease
4) evaluate effectiveness of prevention and treatment activities
Fixed population
a population whose membership is permanent
ex) population of Hiroshima, Japan during atomic bomb explosion in WWII
Dynamic or open population
membership of this population is defined by a changeable state or condition
ex) resident of Boston
Steady state
the number entering a population is equal to the number leaving
ex) BU student population
Count
simplest and most frequently performed quantitative measure
refers to the number of cases of a disease or other health phenomenon
for rare diseases or symptom presentations (cases of Ebola virus)
ex) 5000 cases of influenza in Suffolk county in Jan. 2001
ex) 3000 traffic fatalities in Springfield, IL in 2001
Proportion
for a count to be descriptive of a group, it must be seen relative to the size of the group
a fraction where the numerator is part/subset of the denominator
ex) male births/all births
Ratio
a relative relationship
like a proportion or a fraction
numerator and denominator are mutually exclusive/not related - different from a proportion
Rate
a fraction that consists of a numerator and a denominator and in which time forms part of the denominator
the numerator is a subset/part of the denominator
involved a measure of time
the numerator is the frequency of disease
the denominator is a unit size of population, over a specified time period
Rate purpose
Contain the following 3 elements:
1) disease/health event frequency
2) unit size of population
3) time period
Crude rates
summary rates based on the actual number of events in a population over a given time period
Crude birth rates
number of live births within a given period / population size at the middle of that period
General fertility rate
of live births within a year / # of women aged 15-44 years during the midpoint of the year
Infant mortality rate
number of infant deaths among infants aged 0-365 days during the year / number of live births during the year
Neonatal period
neonatal period: birth - 28 days of age
Neonatal mortality rate
number of infant deaths under 28 days of age / number of live births
reflects consequences of perinatal events, primarily:
- congenital malformations
- prematurity (birth before gestation week 37)
- low birth weight (birth weight less than 2,500 g)
Postneonatal mortality rate
reflects environmental events, control of infectious diseases, and improvement in nutrition
Fetal death rate
used to estimate the risk of death of the fetus associated with the stages of gestation
number of fetal deaths after 20 weeks or more gestation / number of live births and number of fetals deaths after 20 weeks or more gestation
Late fetal death rate
number of fetal deaths after 28 weeks or more gestation / number of live births and number of fetal deaths after 28 weeks or more gestation
Perinatal mortality rate
reflects environmental events that occur during pregnancy and after birth; it combines mortality during the prenatal and postnatal periods
Maternal mortality rate
reflects health care access and socioeconomic factors; it includes maternal deaths resulting from causes associated with pregnancy and puerperium (during and after childbirth)
(number of maternal deaths assigned to causes related to childbirth / number of live births (during a year)) x 100,000
per 100,000 live births, including multiple births
Crude rates
use crude rates with caution when comparing disease frequencies between populations
observed differences in crude rates may be the result of systematic factors within the population rather than true variation in rates
Different types of rates
1) crude rates
2) specific rates
3) adjusted rates
Who started natural experiments
John Snow (mid 19th century)
cholera outbreak
John Snow’s natural experiment
linked the cholera epidemic to contaminated water supplies
used a spot map of cases and tabulation of fatal attacks and deaths
observe and record data (quantitative approach)
two different water companies supplied water from the Thames River to houses in the same area
The Lambeth Company moved its source of water to a less polluted portion of the river
during the next cholera outbreak those served by the Lambeth Company had fewer cases of cholera than in prior outbreaks
Natural experiment
the epidemiologist does not manipulate a risk factor but rather observes the changes in an outcome as the result of natural occurring situation
City A: population 500,000 reports 1,000 new cases of prostate cancer in 1-year period
City B: population 50,000 reports 750 new cases of prostate cancer in a 3-year period.
Which city has the higher rate of new prostate cancer cases?
1000/500000 = 0.002
0.002 x 1000 = 2
750/50000 = 0.015
- 015 / 3 = 0.005
- 005 x 1000 = 5
City B has a higher rate of new prostate cancer cases
Limitations of Crude Rates
observed differences may be due to systematic differences (age, gender, race) between the populations rather than true variations in rates
How to correct crude rates
specific rates and adjusted rates
Specific rates
refer to a particular subgroup of the population defined in terms of race, age, sex, or single cause of death or illness
may also examine cause specific morbidity and mortality rates within a subgroup of the population
ex) mortality from HIV among 25-34 year olds
Age specific death rate
(number of deaths in age group / number of persons in age group) x 100,000
Cause-specific rate
(mortality (or frequency of a given disease) / population size at midpoint of time period) x 100,000
Cause Specific Mortality
the number of deaths from a disease or cause divided by the population size at the mid-point of the time period
shows the risk of mortality from a specific cause within that population
IS a measure of risk of dying of a specific disease/cause
Proportional mortality ratio
(mortality due to a specific cause during a time period / mortality due to all causes during the same time period) x 100
the number of deaths within a population due to a specific disease or cause divided by the total number of deaths in the same population during a specific time period
indicates relative importance of a specific cause of death; NOT a measure of the risk of dying of a particular cause
Country A and B have identical populations (1 million) and cause specific mortality for cardiovascular disease (CVD): 5 per 100,000.
Risk of dying from cardiovascular disease is the same for both countries
Yet PMR from CVD is:
16.6% in Country A
50% in Country B
A: overall mortality rate = 30 per 100,000
B: overall mortality rate = 10 per 100,000
How can this be?
Need to know each country’s mortality rate to calculate total number deaths in each community:
A: overall mortality rate = 30 per 100,000
B: overall mortality rate = 10 per 100,000
Need to know total deaths for each country to calculate each country’s PMR
A: 30/100,000 X 1,000,000 (total population)
total deaths = 300
B: 10/100,000 X 1,000,000 (total population)
total deaths = 100
Cause specific mortality for cardiovascular disease is 5 per 100,000. (i.e. 50 per 1,000,000, total number of deaths from CVD in each country.
A: PMR = 50/300 = .166 X 100 = 16.6%
B: PMR = 50/100 = .5 X 100 = 50%
Uses of PMR
determine priorities in health care planning within a population (administrator)
indicate an area for further study (epidemiologist)
Adjusted rates
rates that have been modified statistically to remove the effect of differences in population composition, such as differences in age, sex, or income across various populations to allow comparisons
Direct Method for Age Adjustment
may be used if age-specific death rates in a population to be standardized are known and if a suitable standard population is available
Direct Standardized Mortality Ratio (DSMR)
(age adjusted mortality rate of test communiity / crude mortality rate of standard pop) x 100
ex) (17.0/12.5) x 100 = 136
“the mortality experience of Community C was thirty six percent (36%) higher than that of Community A)
When to age adjust
1) age must be related to mortality (or morbidity)
2) age distribution of the 2 populations being studied must be different
Standardization for mortality rates may also be appropriate for other factors (sex, ethnic group) … IF both conditions apply
1) sex is related to mortality
2) sex distribution of both populations being studied is known and differs
Why should we collect population data?
Estimating parameters of:
- health
- morbidity
- mortality
Census data purpose
provides information on the general, social, and economic characteristics of the US population
administered every 10 years
attempts to account for every person and his or her residence
characterizes population according to sex, age, family relationships, and other demographic variables
Vital statistics
births, deaths, fetal deaths, marriages, divorces
Statistics derived from the vital registration system
mortality statistics
birth statistics: certificates of birth and fetal deaths
Limitations of mortality data
overall death certificates are accurate BUT
stigma associated with certain diseases may lead to inaccurate reporting (underreporting)
Where errors occur:
errorrs in coding
lack of standardization of diagnostic criteria
changes in coding
Premature mortality rate
deaths before age 75
rates are per 100000 population
Rationale
focusing on deaths to persons less than 75 years - more preventable deaths
Summary health statistic
excellent measure to reflect the health status of a population
Birth certificate information
includes information that is relevant to the health of the neonate, such as congenital malformations, birth weight, and length of gestation
sources of unreliability:
- mothers’ recall of events during pregnancy may be inaccurate
How many notifiable diseases are there in the US?
more than 60 notifiable diseases in US
Limitations of reportable disease statistics
possible incompletness of population coverage
failure of MD or other provider to fill out required forms
unwillingness to report cases that carry a social stigma
Registry
a centralized database for collection of data about a disease
coding algorithms are used to maintain patient confidentiality
applications:
- patient tracking
- identification of trends in rates of disease
Surveillance, Epidemiology, and End Results (SEER) program
- conducted by National Cancer Institute (NCI)
- collects cancer data from different cancer registries across the US
provides information about trends in cancer incidence, mortality, and survival by geographic and demographic characteristics
General Population Surveys
collect data on the health status of a population group
obtain more comprehensive information than would be available from routinely collected data
ex) national health survey
Behavioral Risk Factor Surveillance System (BRFSS)
telephone health survey system, tracking health conditions and risk behaviors in the US since 1984
issues such as asthma, health care access, alcohol use, obesity, cancer screening, nutrition and physical activity, tobacco use
National Health Survey
authorized under the National Health Survey Act of 1956 to obtain information about the health of the US population
conducted by the NCHS; consists of three programs
Household Interview Survey (HIS)
general household health survey of the US civilian noninstitutionalized population
studies a comprehensive range of conditions such as diseases, injuries, disabilities, and impairments
Health Examination Survey (HES)
provides direct information about morbidity through examinations, measurements, and clinical tests
identifies conditions previously unreported or undiagnosed
provides information not previously available for a defined population
Screening Surveys
conducted on an ad-hoc basis to identify individuals who may have infectious or chronic diseases
ex) breast cancer screenings, health fairs
clientele are highly selected
individuals who participate are concerned about the particular health issue
not representative of general population
Insurance Data information
social security - provides data on disability benefits and Medicare
health insurance - provides data on those who receive care through a prepaid medical program
life insurance - provides information on causes of mortality; also provides results of physical examinations
Limitations of insurance data
data may not be representative of entire population
Hospital data
consists of both inpatient and outpatient data
deficiencies of data:
- not representative of any specific population
- different information collected on each patient (improving - standardized)
- settings may differ according to social class of patients
Data from Physicians’ Practices
limited application due to:
- confidentiality of patient data
- highly selected group of patients
- lack of standardization of information collected
useful for:
- verification of self-reports
Absenteeism Data
records of absenteeism from work or school
possible deficiencies:
- data omit people who neither work nor attend school
- not all people who are ill take time off
- those absent are not necessarily ill
- useful for the study of rapidly spreading conditions - flu epidemic
Criteria for the quality and utility of epidemiologic data
1) nature of the data
2) availability of the data
3) completeness of population coverage
4) value and limitations
Representativness (external validity)
generalizability of findings to the population from which the data have been taken
Thoroughness
the extent to which all cases of a health phenomenon have been identified
HIPAA Privacy Rule
protects all “individually identifiable health information” including demographic data that relates to:
Past, present, or future physical or mental condition
provision of health care to the individual
past, present, or future payment for provision of health care to the individual
Data Interpretation
Consider when interpreting data:
1) population, about which information was obtained
2) calendar (time) period covered
3) level of missing or inaccurate data
Youth Surveillance Data in Massachusetts
Gambling
Sports-related traumatic brain injury
tobacco and marijuana
Massachusetts Mortality Data
overall mortality rates and life expectancy
causes of death
opioid-related deaths
premature mortality rate
Youth Survey Data
collect demographics, health behaviors, and risk factors
important data source for prevention programs at the Department of Public Health
conducted odd years
Massachusetts currently conducts:
Youth Health Survey (YHS)
Youth Risk Behavior Survey (YRBS) - CDC-based survey, most questions comparable with US and other states
YHS (Youth Health survey) and YRBS (Youth Risk Behavior Survey) data limitations
- self reported
- cross sectional: should not be used to determine causation
- only a sample of MA public schools
- does not include students in: private schools, state custody, other educational settings
- underrepresent students who: have severe limitations or disabilities, are often absent from school
subjected to biases: sampling, non-sampling, non-response
Youth Surveillance Data
provides a picture of current health and risk behaviors of youth
able to determine areas that need improvement and discover emerging issues
data is a key tool for programs to tailor interventions and focus preventive efforts
over time, data shows advancements made by programmatic efforts
APC (Annual Percent Change)
rates are assumed to change at a constant percentage of the rate of the previous year
Is Pain a part of the vital signs
Yes, started in 1995
related to opioid crisis
Purdue role in opioid crisis
generated $31 billion in revenue from OxyContin for Purdue
did not stop marketing OxyContin to doctors until 2018
Opioid crisis emerged in 3 waves
initially a crisis of prescription opiods
heroin becomes more of a factor
explosion of synthetic opioids
Opioid Epidemic meets COVID-19
drug overdoses spiked 18% in the US from mid-March through mid-May
more than 40 states have reported increases in opioid-related mortality
isolation, social distancing, job loss, delayed elective surgeries
Health Disparities
are preventable differences in the burden of disease, injury, violence, or opportunities to achieve optimal health that are experienced by socially-disadvantaged populations
are the result of upstream factors embedded in social institutions and practices - such as racism, classism, sexism, and socioeconomic inequalities
Health disparity factors
- poverty
- environmental threats
- inadequate access to health care
- individual and behavioral factors
- educational inequalities
- race or ethnicity, sex, sexual identity, age, disability, socioeconomic status, geographic location
Medical system bias
non-white patients are less likely to receive pain treatment and be prescribed opioids than white patients
Descriptive Epidemiology
distribution of disease
Characterize health outcome by person, place, time
2 Main uses of Descriptive Epidemiology
1) generate hypotheses about causal relationships - a tentative explanation for an association between pattern of disease in the population and a risk factor or cause
ex) higher rates of obesity and diabetes in southern US states
2) public health planning and evaluation
Biologic clock phenomenon
waning of the immune system may result in increased susceptibility to disease, or aging may trigger appearance of conditions believed to have genetic basis
Latency period
age effects on mortality may reflect the long latency period between environmental exposures and subsequent development of disease
Sex Differences
all cause and age specific mortality rates higher for men than for women
mortality rate higher for men than for women
death rates for both sexes are declining
Female Paradox
indicates female age-standardized morbidity rates for many acute and chronic conditions are higher than rates for males… even though mortality is higher for males
Marital status
married people have lower rates of morbidity and mortality
Marriage may operate as:
protective - may provide an environment conducive to health
selective - people who marry may be healthier to begin with
African American Statistics
highest rate of mortality of all groups studied in the US
higher blood pressure levels
age-adjusted death rate for African Americans was 1.3 times rate for whites in 2003
differences in life expectancy
American Indian Statistics
infectious disease is the 10th leading cause of death
death rate is 6.6 times that for all races in US
Asian Statistics
Japanese demonstrated lower mortality rates
lower rates of congenital heart disease and cancer
low CHD rates attributed to low-fat diet and institutionalized stress-reducing strategies
some Asian groups have high smoking rates
Acculturation
defined as modifiations that individuals or groups undergo when they come in contact with another country
provide evidence of the influence of environmental and behavioral factors on chronic disease
Nativity
place of origin of the individual
Healthy Migrant Effect
observation that healthier, younger persons usually form the majority of migrants
Socioeconomic Status
low social class is related to excess mortality, morbidity, and disability rates
factors include:
- poor housing
- crowded conditions
- racial disadvantage
- low income
- poor education
- unemployment
Measurement of social class
prestige of occupation or social position
educational attainment
income
combined indices of two or more of the above variables
Mental Illness/SES
association of socioeconomic status and mental illness (Hollingshead and Redlich)
Hollingshead and Redlich Findings
Strong inverse association between social class and likelihood of being a patient with mental illness under treatment
as social class increased, severity of mental illness decreased
type of treatment varied by social class
Social causation explanation
conditions associated with lower social class produce mental illness
Downward drift hypothesis
persons with severe mental disorders move to impoverished areas
Other correlates of Low Social Class
higher rate of infectious disease
higher infant mortality rate and overall mortality rates
lower life expectancy
larger proportion of cancers with poor prognosis
Secular Time Trends
refer to gradual changes in the frequency of a disease over long time periods
ex) decline of heart disease mortality in the US
Clustering
refers to an unusual aggregation of health events grouped together in space and time
Examples of temporal clustering
post-vaccination reactions, postpartum depression
Examples of spatial clustering
concentration of disease in a specific geographic area
Time (pattern)
temporal patterns in disease occurence may lead to improved understanding of disease causation and recognition of emerging epidemics
Epidemic
unusually high level of disease occurrence in a population in the light of past experience
ex) influenza, HIV
Pandemic
worldwide epidemic
Social Progress Index
basic human needs, foundations of wellness, opportunity
a way to measure wellbeing of a country
better than GDP
Ways to measure disease outbreaks
attack rate
secondary attack rate
case fatality rate
Attack rate equation
(sick / population at risk) x 100 (during a time period)
Secondary attack rate equation
(total case - initial cases / total pop at risk - initial cases) x 100
Index case
case that first comes to the attention of public health authorities
Coprimaries
cases related to index case so closely in time that they are considered to belong to the same generation of cases
Initial cases
index case(s) + coprimaries
Secondary attack rate
an index of the spread of disease within a family, household, dwelling unit, dormitory or similar circumscribed group
1) a measure of contagiousness
2) used to evaluate control measures
3) very useful measure in infectious disease control
Uses for attack rates
commonly used to describe occurence of food borne illness, infectious diseases, acute epidemics
Case Fatality Rate (CFR)
the number of deaths caused by the disease among those who have the disease
Case Fatality Rate (CFR) equation example
(number of meningitis deaths / number of meningitis cases) x 100
Endemic
usual/typical level of disease occurrence in a population
the 3 parts of the Epidemiologic Triangle
host, agent, environment
Agents (examples)
bacteria, viruses, mycoses (fungal diseases), protozoa, helminths
Characteristics of Infectious Disease Agents
1) Infectivity
2) Pathogenicity
3) Virulence
4) Toxigenicity
5) Resistance
6) Antigenicity
Infectivity
the capacity of an agent to enter and multiply in susceptible host
measured by the attack rates, specifically secondary attack rates
high infectivity = when secondary attack rate of a disease is high = measure of contagiousness
Pathogenicity
capacity of the agent to cause disease in the infected host
measured by the proportion of infected individuals with clinically apparent disease
high pathogenecity = low rate of subclinical cases among those infected (ex. measles)
low pathogenicity = high rate of subclinical cases among those infected (ex. polio)
Virulence
refers to the severity of a disease
measured by the proportion of cases that are severe or fatal cases (if fatal, use case fatality rate)
Toxigenicity
the capacity of the agent to produce a toxin or poison
Resistance
the ability of the agent to survive adverse environmental conditions
Antigenicity
the ability of the agent to induce antibody production in the host
Host definition
a person (or animal) who permits lodgment of an infectious disease under natural conditions
Host Defense Mechanisms
nonspecific (barriers) - skin, tears, mucosal surfaces, saliva, gastric juices
specific - immune system
Active immunity
microorganism or a modified part of the microorganism invokes an immunologic response by the host
when the host makes the antibodies him/herself
long-term
Passive immunity
short term immunity provided by a preformed antibody, which is delivered to the host
when the host receives pre-formed antibodies
short-term
Natural, active immunity
results from an infection by the agent
Artificial, active immunity
results from a vaccine that stimulates antibody production in the host
Natural, passive immunity
preformed maternal antibodies pass to the fetus during pregnancy
provides short-term immunity in the newborn
Artificial, passive immunity
preformed antibodies are given to exposed individuals to prevent disease
Environment
the domain external to the host in which the agent may exist, survive, or originate
consists of physical, climatologic, biologic, social, and economic components that affect the survival of the agents and serve to bring the agent and host into contact
can act as a reservoir that fosters the survival of infectious agents
ex) contaminated water supplies or food; soils; vertebrate animals
Animal Reservoirs
animals can be reservoirs of infectious agents
Zoonoses
infectious diseases that are potentially transmittable to humans by vertebrate animals
ex) rabies and the plague
Direct transmission
spread of infection through person-to-person contact
Portal of entry
locus of access to the human body
ex) mouth and digestive system
Portal of exit
site where infectious agents leave the body
ex) respiratory system, skin lesions
Indirect transmission
the spread of infection through an intermediary source
ex) vehicles, fomites (inanimate objects laden with disease-causing agents), vectors (living insects or animals involved with transmission of the disease agent)
Inapparent/Subclinical infection
no symptoms of infection present
important because disease can be transmitted by infected but asymptomatic individuals
Herd immunity
group immunity
immunity of a population, group, or community against an infectious disease when a large proportion of individuals are immune either through vaccinations or prior infection
Infectious disease spread
1) the number of susceptible people
2) the likelihood that a susceptible person will come in contact with someone who is infected
Incubation period
time from invasion of infectious agent to development of signs and/or symptoms of the infectious disease in the host
Iceberg concept of infection
active clinical disease accounts for only a small proportion of host infections and exposures to disease agents
3 types of data to link illnesses to contaminated foods and solve outbreaks
Epidemiologic
Traceback
Food and Environmental Testing
Isolation
separates sick people with a contagious disease from people who are not sick
Quarantine
separates and restricts the movement of people who were exposed to contagious disease, usually through a sick person, to see if they become sick
