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Humbio 151

Epidemiology (1) investigation of chronic diseases (eg heart disease, cancer) and outbreaks (eg swine flu, salmonella)
Epidemiology (2) basic methodology to instigate public health research
Epidemiologic process 1. describe disease risks and trends 2. explain the factors responsible 3. make predictions - health policy & planning 4. instigate control and prevention initiatives 5. evaluate control/prevention 6. advocate and influence policy
shoe-leather epidemiology gumboot, field-epi - case studies
miasma bad air (agent of spread)
index case aka patient zero/primary case the initial patient in the population sample of an epidemiological investigation
epidemic curve (1) graphic depiction of the number of outbreak cases by date of illness onset
epidemic curve (2) provides info on: 1. pattern of disease spread 2. outbreak magnitude 3. time trend 4. outliers 5. disease incubation period
common source cases acquire the infection from the same source
intermittent common source epi curve irregular peaks reflecting the timing and extent of exposure
continuous common source epi curve often causes epi curve to rise gradually and perhaps plateau
point common source epi curve -brief period of exposure, all cases occur within one incubation period -typically shows abrupt upward slope and subsequent decline
norovirus incubation period 12-48 hours
Campylobactor incubation period 48-96 hours
tick borne relapsing fever ground squirrels agent: borrelia hermsii
case fatality ratio number of deaths/number of cases
SARS agent coronavirus
nosocomial hospital related disease transmission
prevalence number positive / number tested number positive samples / sample size
anatomy of disease DREEMS 1. Susceptible hosts 2. Disease agent 3. Reservoir/source 4. Entry into susceptible host 5. Exit from infected host 6. Mode of transmission
disease agents 1. viruses 2. bacteria 3. fungi 4. parasites 5. prions 6. cancer cells 7. pollutants 8. malnutrition/poverty
reservoir/source 1. humans 2. animals 3. environment
true multi-host pathogens brucellosis bison <--> cattle
spillover (dead-end) hosts WNV from birds to humans birds --> humans
apparent multi-host pathogens frequent spillover domestic dogs --> jackals
emerging infectious disease infrequent spillover, high subsequent transmission chimp --> human <--> human
typhoid fever agent Salmonella typhi
infectivity ability of a disease agent to cause infection in a susceptible host
pathogenicity ability of a pathogen to cause disease (onset of harmful symptoms)
virulence the severity of the disease / fatality ratio / proportion of cases that develop disease
modes of disease transmission 1. contact (direct/indirect) 2. droplets 3. airborne 4. vector-borne 5. vehicle-borne (food and/or water) 6. vertical
entry into susceptible host 1. contact 2. airborne 3. vectors 4. food/water 5. vertical transmission
cluster observation of above normal number of cases
outbreak sudden increase in disease cases
epidemic outbreak on scale, depends on who is working on the disease
pandemic outbreak at international/global scale
endemic normal/baseline natural distribution or rates of disease
epizootic epidemic in wildlife
enzootic endemic in wildlife
number of people suffering from disease 1. tells present scale of problem 2. meaningful for advocacy 3. logistically informative
point prevalence infected cases at census point
period prevalence infected cases during census period (existing and new infections)
incidence (1) number of new cases that occur during a specific period of time in a population at risk for developing disease
person-time units length of time individuals are in states of health, exposure (at risk), infection, infectiousness, etc.
incidence (2) # cases / person-time @ risk
cohort well defined group of subjects or patients who have had a common experience or exposure and are then followed up for the incidence of new diseases or events
fixed cohort all people present at beginning of study; no new entries
open cohort people can enter study at any time
epidemiologic surveillance ongoing systematic collection, analysis, and interpretation 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
who recognizes outbreaks? 1. medical practitioners 2. patients and families 3. public health surveillance data 4. local media 5. internet
case ID confirming a disease agent 1. isolate disease agent from host 2. identify the disease agent
tools to identify the disease agent 1. culture 2. infection 3. microscopy 4. PCR 5. pulsed-field gel electrophoresis (PFGE) 6. antibody
PFGE(1) 1. DNA chromosome restricted by enzymes into 10-20 fragments 2. pulsed voltage 3. gel separates DNA fragments 4. run positive control 5. record image, compare in BioNumerics
PFGE(2) 1. simple to perform 2. universal sub-typing method 3. high discrimination 4. high reproducibility within and between labs 5. 'gold standard' of molecular sub-typing methods
problem with lab tests positive results 1. target is present 2. contamination 3. random events negative results 1. target is absent 2. failure to work 3. random events
test validity the ability to distinguish between presence and absence of a disease
sensitivity ability of test to correctly identify cases that have the disease
specificity ability of the test to correctly identify cases that do not have the disease
test validity influenced by 1. test type 2. sampling time of test 3. prevalence of the disease (rare or common) 4. number of times test is performed
PPV positive predictive value - how likely is a given positive test result likely to be a true positive
case investigation 1. verify that an outbreak is occurring 2. establish preliminary hypothesis 3. make case definition 4. case finding 5. case questionnaires 6. organize data (line listing) 7. describe current outbreak information
cause investigation systematically review 1. disease agent 2. reservoir/source conduct: LEVEL laboratory investigations epidemiologic/clinical investigations veterinary/wildlife/vector investigations environmental investigations law enforcement investigations
risk factor aka determinant, a variable associated with an increased risk of disease or infection
factors influencing epi spatial: physical distribution of a disease in an area seasonality human risk factors
human disease risk factors 1. sex 2. age 3. race 4. socioeconomic status 5. culture 6. class 7. behavior 8. beliefs
disease risk factors for chronic diseases 1. tobacco 2. diet 3. obesity 4. reproductive and hormonal factors 5. viruses, bacteria, etc. 6. occupational hazards 7. environment 8. genes
ecological fallacy inferences about the nature of specific individuals are based solely upon aggregate statistics collected for the group to which those individuals belong
guidelines for causality (1) 1. temporal relationship: exposure to the factor must precede sickness/health 2. strength of association: stronger (risk/odds ratio) implies causal relationship 3. dose-response relationship: if risk of disease increases with dose of exposure
guidelines for causality (2) 4. reproducible findings: if relationship is causal, it should be evident in different studies and different populations 5. biologic plausibility: epi findings must be consistent with existing biological knowledge
guidelines for causality (3) 6. consideration of alternate explanations: take into account and rule out other possibilities 7. cessation of exposure: risk of disease should decline when exposure to the factor is reduced or eliminated 8. consistency with other knowledge
guidelines for causality (4) 9. specificity of the association: relationship is between causal factor and a certain specific disease
retrospective cohort disease outbreak is occurring
prospective cohort -looking forward, does not self select who got the disease - academic, usually chronic diseases
case-control study -ask cases and controls the same questions about exposures -calculate odds ratio -quick alternative to large cohort studies
suspected case clinically compatible case without presumptive or confirmatory lab results
probable clinically compatible case with presumptive lab results
confirmed clinically compatible case with confirmatory lab results
contact tracing process of locating and notifying partners (contacts) that have exposed to disease
line listing -common file for information -each case = 1 row -cases and noncases -updated through investigation -every row a unique ID
methods of disease control (1) 1. isolation 2. vaccination 3. barriers 4. eradication 5. treatment 6. education
methods of disease control (2) reduce Ro by altering 1. duration of infectiousness 2. contact rate 3. transmission probability
anatomy of disease control 1. reduce number of susceptible hosts 2. reduce sources of infection 3. reduce infectiousnes 4. reduce contact rates 5. interrupt transmission 6. increase herd immunity
plague agent Yersinia pestis most lethal bacterium known to man
modes of transmission 1. contact 2. respiratory droplets/secretions 3. airborne 4. vehicle-borne 5. vector-borne 6. vertical transmission
entry/exit into susceptible host 1. contact 2. airborne 3. vectors 4. food/water 5. vertical transmission
Ro basic reproductive number - average number of secondary infectious cases produced by an index case in a susceptible population
population disease categories 1. susceptibles 2. infected 3. removed
R effective reproductive number - average number of secondary infectious cases produced by infectious cases
Rc control reproductive number - effective reproductive number in presence of control measures
herd immunity threshold vaccinating a proportion of the population protects unvaccinated individuals
passive surveillance health officials report cases of illness, but no special effort is made to find unsuspected disease incidents
active surveillance field investigation of disease incidence
lyme disease -agent: borrelia burgdorferi (spirochete) -mode of transmission: vector-borne -reservoir/source: zoonotic disease (rodents)
vaccination 1. reduces number of susceptible hosts 2. reduces sources of infection 3. reduces contact rates 4. interrupts transmission 5. increases herd immunity
childbirth epi
structural violence systemic ways in which a given structure or social institution kills people slowly by preventing them from meeting their basic needs
health and media - real vs. perceived risk - evaluating scientific claims - importance of working with the public and governments to achieve PH goals
environmental disease -environmental hazards may induce acute/chronic responses to exposure -patterns are highly predictable based on the mechanism of the hazard -some hazards may produce both -share pathologic features of disease caused by other factors
definition of disaster - 10 or more dead - 100 or more affected - declaration of a state of emergency - request for international assistance
types of disasters 1. geophysical 2. meteorological 3. hydrological 4. climatologically 5. biological 6. extra-terrestrial
principles of disaster risk reduction risk = hazard + exposure + vulnerability
infant mortality number of infant deaths (<1 year) per 1,000 live births
average length of pregnancy 280 days/40 weeks
perinatal period end of 22 weeks of gestation until end of 7 days after birth
neonatal period birth to 28 days later
stillbirth or fetal death death prior to the complete expulsion or extraction from its mother
perinatal deaths deaths in first week of life and stillbirths
Created by: claudiachern