2 Epidemiology is:The study of the distribution and determinants of health-related states or events in specified populations and the application of this study to the control of health problems.Using data to answer questions of:Who is getting sick?What is making them sick?How can we use this information to reduce the risk of others getting sick?
3 Disease surveillanceThe ongoing systematic collection, analysis, and interpretation of outcome-specific data for use in planning, implementation, and evaluation of public health practice.”Data collected in a surveillance system can be used for many purposes, including:To estimate the magnitude of a health problem in a populationTo understand the natural history of a diseaseTo detect outbreaks or epidemicsTo document the distribution of a health eventTo test hypotheses about causes of diseaseTo monitor changes in infectious organisms
4 Epidemiology is: The study of disease at a population level Endemic vs foreign diseaseSporadic vs epidemic vs pandemicDisease outbreaksRate of diseaseIncidencePrevalenceRisk factorsRelative riskOdds ratio
5 Relative riskThe risk of an event (i.e., developing a disease) relative to exposureA mathematical equation:RR = probability of disease occurring in exposed individuals/ probability in non-exposed
6 Odds ratioA measure of association: compares the odds of disease in those exposed to the odds of disease in those not exposed:OR = odds of disease in exposed/odds of disease in non-exposedAn OR of 1 = no difference between groups, so no association between hypothetical exposure/cause and outcome = illness
7 Probability vs odds?The probability that an event will occur is the fraction of times you expect to see that event in many trials. Probabilities always range between 0 and 1.The odds are defined as the probability that the event will occur divided by the probability that the event will not occur.
12 Epidemiology of disease PathogenHostVirulence factorsDoseIncubation periodSusceptibility to a specific pathogen: receptorsAcquired immunityActive vs passiveNatural vs vaccinationHerd immunityGeneral health statusAgeGeneticsCulture
13 Types of epidemiologic studies Descriptive: who, what, where & whenAnalyticalCross sectionalRetrospectiveProspectiveExperimentalMolecular
14 Cholera outbreak in Haiti 2010 Identifying the source of the outbreak: a combination of analytical and molecular epidemiology
15 Infectious disease surveillance National Disease Surveillance NetworkInternational Society for Infectious Diseases: ProMED:CDC: Morbidity and Mortality Weekly Report(MMWR):Public health departmentsWHO
16 Emerging infectious diseases Novel diseases in a population OR diseases that have a recently increased incidence and/or distributionNew vs newly recognized
17 Emerging infectious diseases Changes in microbesMicrobial evolution: acquisition of virulence factors, antimicrobial resistance, evasion, invasion or exit strategiesExpansion of microbial and vector distributionExpansion of host rangeEnvironmental changesChanges in hostsComplacencyGlobal travelPopulation expansionNew forms of crowding together in small spaces (i.e., daycare centers)
18 Cryptococcus neoformans var. gattii Increased incidence of cryptococcosis in healthy individualsSpike in human cases preceded by a spike in canine cases
19 Healthcare associated infections These come from:Other patientsHealthcare environmentHealthcare workersPatient’s own microbiota
20 Infectious disease transmission in a health care setting Medical devices = fomitesHealthcare personnel = direct transmissionAirborne transmission