BIOL 2460 - chapter 16 - PARKS - MICROBIOLOGY

Parks UTA

Epidemiology

Field that studies distribution & timing of diseases (infectious & non-infectious); determines etiology, transmission, and susceptible populations

Etiology

study of the causes of disease

Morbidity

# of individuals w/ disease

Morbidity rate

#/pop; %

Mortality

# of deaths from disease

Mortality rate

#/pop; %

Prevalence

no. individuals at certain time

Incidence

no. of new cases

Patterns of Incidence

Sporadic, Endemic, Epidemic, Pandemic

Sporadic

occurs occasionally w/o regional concentration (random)
i.e. Tetanus, rabies, plague

Endemic

constantly present in certain region (usually at low levels)
i.e. Malaria, Ebola, chicken pox

Epidemic

larger than normal amount of cases
i.e. Influenza, West Nile

Pandemic

epidemic that is cross continental
i.e. Virulent influenza, Ebola, etc. (COVID)

NNDSS (in the U.S.)

All cases MUST be reported by physicians
Ex: West Nile, HIV, measles, etc.
Studies track notifiable disease to determine risks

CDC

publishes Morbidity and Mortality Weekly Report (MMWR)
Provides physicians and health-care workers with updates on public health issues and latest data on notifiable diseases

John Snow

father of epidemiology; cholera in London 1854

Florence Nightingale

Determined many deaths were from poor sanitation, not battle

Joseph Lister

used epidemiology data of handwashing for better healthcare practices (carbolic acid/aseptic conditions)

Common source

single source for all infected indiv.
Broad Street water pump

Point source

common source that exists for short-time (< pathogen incubation)
potato salad

Continuous source

continuous contamination
sewage from upstream of cholera in London

Intermittent source

on and off
rainfall runoff

Propagated

direct or indirect person to person contact
no single source

Observational

not manipulated
Descriptive
Analytical
Cohort Method
Case-control
Cross-sectional

Experimental

subjects are manipulated; clinical trials; ethical concern, best evidence for etiology, double-blind studies

Descriptive

gathers info about disease outbreak
- Includes interviews & examination of medical records (family history)
- Helps develop hypothesis for etiology/causation

Analytical

selects group to evaluate hypothesis
Retrospective – data from past groups (history)

Prospective – date from current subjects moving forward (looking at it as it is going forward

Cohort method

group-based
examines individuals who share a particular characteristic
Prospective or retrospective

Case-control

group-based
compares groups w/ disease to group w/o
Commonly retrospective

Cross-sectional

group-based
group is randomly selected, compares disease and no disease at a point in time
Looks for associations of measurable variable(s) and the disease

Non-living

soil, water; Ex. Clostridium spp. in soil

Living

humans, animals; Ex. Viruses, enteric microbes

Carriers

living reservoirs (Long persisting pathogens must live somewhere)

Passive

transmits mechanically; is not infected
- failing to wash hands

Active

infected host transmits during incubation or convalescence
- transmission before/after fever
Asymptomatic – active carrier w/o symptoms
- early HIV, typhoid Mary aka Mary Mallon

Definitive host

Parasitic infection: preferred host; parasite reaches sexual maturity

Intermediate host

Parasitic infection: can include one or more; parasite goes through immature life cycle stages

Contact transmission

Direct contact transmission – person to person
- Vertical – mother to child
- Horizontal – other person to person contact
- Droplet – transmission in droplets at 1 meter or less
Indirect contact transmission – fomite to person
- Ex. Sexually transmitted = direct & horizontal
- Ex. Birth = direct & vertical
- Ex. Cough @ short range = direct & droplet
- Ex. Cough onto desk = indirect

Vehicle transmission

through water, food, or air
Ex. Aerosols; Hantavirus
Ex. Longer lasting droplets; tuberculosis

Vector Transmission: Mechanical transmission

animal vector (not infected) carries pathogen from one host to another;
- Mechanical vector ; Ex. fly that lands on feces & food,
arthropod

Vector Transmission: Biological transmission

pathogen reproduces in vector that transmits pathogen from one host to another
- Biological vector ; Ex. mosquitoes that pick up West Nile

Quarantined

isolation of infected or exposed individuals to prevent transmission of the disease
- Duration is determined by incubation period & evidence
of infection

healthcare-associated infections (HAI)

Nosocomial: Commonly introduced through contaminated medical equipment (e.g. catheters, respiratory ventilators, etc.)

Agencies Monitoring Global Health

WHO, CDC, EU Health Security Committee
- Provide logistical support and response in case of
epidemic/pandemic
- Identify emerging & re-emerging diseases

Emerging infectious disease

new to population or shown increase in prevalence in last 20 yrs
Ex: Ebola (2015), Coronavirus (2020)

Re-emerging infectious disease

increase after period of decline
Ex: drug resistant tuberculosis
Ex: measles; decline in vaccinations