Ch.10.1-2 Epidemiology Microbiology

10.1 History of Epidemiology Epidemiology is the study of patterns, causes, and effects of health and disease conditions in defined populations. Identifies risk factors and provides targets for preventative medicine. Developed methodology used in clinical research and public health studies. Greek physician Hippocrates was first recorded epidemiologist. Epidemic-”visited upon” Endemic-”reside within” Syndemic-interaction of diseases

10.1 History of Epidemiology 1858 Dr. John Snow, father of modern epidemiology, identified cause and solution to cholera outbreak in London using maps to identify source of contamination. 1954 Mathematical methods were introduced which showed the statistical relationship between lung cancer and smoking.

10.1 The Science of Epidemiology Disease etiology Observational Experimental Disease surveillance Disease screening Biomonitoring Clinical Trials Randomized control Field trials Community trials

10.1 Vocabulary of Epidemiology Outbreak-greater occurrence than expected. Asymptomatic-”carrier”, has no symptoms. Pandemic-disease spread worldwide. Incidence-risk of disease over a period of time. Prevalence-total number of cases in a population. Morbidity-diseased state. Mortality-death rate. Progression: infection, incubation, acute, decline & convalescent periods.

10.1 Koch’s Postulates Four criteria designed in the 1880’s to establish a causal relationship between microbe and disease. Microorganism must be found in abundance in all diseased organisms. Microorganism must be isolated and grown in culture. The cultured microorganism should cause disease when introduced to a healthy organism. The microorganism must be reisolated and shown to be identical to original.

10.1 Exceptions to Koch’s Postulates First postulate abandoned after the discovery of asymptomatic carriers of cholera. The second postulate may be suspend for certain microorganisms that cannot be grown in culture such as prions. The third postulate specifies “should” not “must” because as Koch proved himself not all organisms exposed to the infectious agent will acquire the infection such as in the cases of tuberculosis and cholera.

10.2 Occurrence of a Disease Outbreaks Verify the diagnosis Identify the existence Create a case definition Map the spread Develop a hypothesis Study hypothesis Refine hypothesis Develop and implement control and prevention systems Release findings

10.2 Occurrence of a Disease Outbreak Patterns Common source Continuous source-multiple incubation periods Point source-less than one incubation period Propagated-person to person Other Factors Behavioral risk related- STD’s Zoonotic-vectors

10.2 Disease Severity & Duration World Health Organization (WHO) Scope of disease Localized-only part of the body Disseminated-spread to other parts of the body Systemic-affects the entire body

10.2 Disease Severity & Duration International Classification of Diseases (ICD) Acute-short-lived Chronic-long period of time (6 months min.) Flare-up-recurrence Refractory-resists treatment Progressive-gets worse over time Remission-symptoms stop or lessen for a period of time Cure-complete remission

10.2 Extent of Host Involvement Primary pathogens-cause disease as a result of their presence or activity within the normal healthy host. Intrinsic virulence-need to reproduce and spread Opportunistic pathogens- cause infections in a host with depressed resistance. Genetic defects Exposure to antimicrobial drugs or immunosuppressive chemicals Exposure to radiation

10.2 Identification of Microbes Based on Molecular Genetics Genome-genetic sequence ID Very sensitive Revised Koch’s postulates Nucleic acid sequence present Fewer, or not present in healthy individuals Decrease with resolution Sequence copy number correlates with severity Known biological characteristics Tissue-sequence correlation Reproducible Vaccine development Not yet possible for many pathogenic organisms