Download background notes, pls review before Lecture 20

BIO 208 Microbiology – Unit 3 – Disease Transmission and Epidemiology
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
 Etiology – the cause of a disease
 Etiological agent – the microorganism that causes the disease (synonymous with
pathogen)
 Pathogen – a microorganism that is capable of causing disease
 Pathology – the study of disease
 Pathogenesis – the manner in which a disease develops and progresses
 Infection – invasion or colonization of the body by a pathogen
 Incubation – the time interval between infection and the first appearance of signs and
symptoms
 Symptom – A subjective indication of a disease (something you the patient experiences),
such as feeling hot, tired, achy, nauseous
 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
 Endemic = disease that is constantly present in a population (e.g., measles)
 Epidemic = an unusually large number of cases (every winter we see an epidemic of
Influenza)
 Outbreak = a cluster of cases in a short time period (currently, avian influenza in
southeast Asia)
 Pandemic = an epidemic that spreads worldwide (what we fear may happen with avian
influenza)
1
BIO 208 Microbiology – Unit 3 – Disease Transmission and Epidemiology
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
2
BIO 208 Microbiology – Unit 3 – Disease Transmission and Epidemiology
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).
3