BIO 208 Microbiology – Unit 3 – Disease Transmission and Epidemiology 1
These notes should be reviewed prior to the class on Disease Transmission and Epidemiology.
We will NOT go over this material in class, but it is essential for your understanding of what we will be covering in class.
Medical Microbiology
1. Disease Transmission and Epidemiology – Chapter 14
Disease - change from a state of health a. Terminology related to infectious diseases
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Etiology – the cause of a disease
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Etiological agent – the microorganism that causes the disease (synonymous with pathogen)
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Pathogen – a microorganism that is capable of causing disease
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Pathology – the study of disease
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Pathogenesis – the manner in which a disease develops and progresses
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Infection – invasion or colonization of the body by a pathogen
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Incubation – the time interval between infection and the first appearance of signs and symptoms
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Symptom – A subjective indication of a disease (something you the patient experiences), such as feeling hot, tired, achy, nauseous
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Sign – An objective finding, usually detected on physical examination, from a laboratory test, or x-ray (etc) that indicates the presence of abnormality or disease, such as elevated body temperature (fever), increased respiration rate, elevated white blood cell count, fluid in the lungs, etc.
Epidemiology – the study of disease in populations a. Terminology related to epidemiology
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Endemic = disease that is constantly present in a population (e.g., measles)
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Epidemic = an unusually large number of cases (every winter we see an epidemic of
Influenza)
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Outbreak = a cluster of cases in a short time period (currently, avian influenza in southeast Asia)
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Pandemic = an epidemic that spreads worldwide (what we fear may happen with avian influenza)

BIO 208 Microbiology – Unit 3 – Disease Transmission and Epidemiology 2 b. Reservoirs - where pathogens persist, a continual source of the organism that can fuel cases i. human reservoirs of disease – the primary reservoir of most diseases of humans is the human body itself
 symptomatic – a person exhibiting signs and symptoms of disease and is capable of infecting others
Ex. someone with norovirus gastroenteritis (nausea, vomiting)
 asymptomatic carriers – a person that is not exhibiting signs and symptoms, apparently healthy, but infected and infectious to others.
Ex. people infected with gonorrhea or herpes may be asymptomatic but are still infectious ii. nonhuman reservoirs of disease zoonoses - diseases of animals that can be transmitted to humans
Ex. rabies, salmonellosis iii. environmental reservoirs soil (botulism, tetanus), water (Legionnaire's, cholera), etc iv. hospitals and hospital personnel as reservoirs, especially of antibiotic resistant microorganisms c. Transmission – how pathogens are spread i. by contact a) direct contact – also called person-to-person contact- when 1 person physically touches another
Ex. touching (MRSA infections), sexual contact (STIs) b) indirect - via inanimate objects = fomites – some examples include door knobs, telephones, computer keyboards, tv remotes, etc
Ex. cold viruses and Influenza c) droplet transmission – in droplets coming from the respiratory system (sneezes, coughs)
Ex. tuberculosis, Influenza, SARS ii. by food, water, or fecal contaminated material (fecal-oral) gastrointestinal pathogens incl. waterborne pathogens
 ingestion
 cross-contamination of food preparation materials
Ex. salmonellosis, shigellosis, cholera

BIO 208 Microbiology – Unit 3 – Disease Transmission and Epidemiology 3 iii. airborne (similar to droplet transmission)
Ex. anthrax, histoplasmosis iv. by vectors a) mechanical - vector transfers microbes from one host to another.
Ex. housefly, fleas b) biological - vector is required in microbe's life cycle
Ex. mosquitoes v. nosocomial – acquired as a result of being hospitalized, from the hospital environment or contact with hospital personnel or other patients.
Significant problem!!! 5-15% of all hospitalized patients will develop a nosocomial infection (2 million people per year U.S. and 20,000 deaths).