Chap. 19 -Epidemiology

sporadic

disesase occurs only occasionally

example of sporadic

Botulism

endemic

disease occurs at fairly constant levels

example of endemic (2)

malaria

the common cold

epidemic

disease occurs in unusually high numbers

example of epidemic

influenza

emerging infectious diseases

• newly identified -notable number of cases

• ex:

  • MERS, west nile virus, SARS-CoV-2

reservoir

• source of the infectious agent

  • can be objects (fomites), food, living things

human reservoirs

• people harbour pathogens and transmit them to others

  • germs can be transmitted during any stage of disease

what is considered a stage of disease (5)

• incubation period

• period of illness

• convalescence period

• prodromal period

• period of decline

human reservoir -carrier

• people can also transmit pathogens without having any signs of disease themselves

example of a carrier

• Typhoid Mary -Salmonella typhi

zoonosis

• a disease that occurs in animals, but can be transmitted to humans

examples of zoonosis

• influenza- birds, pigs

• rabies -bats, skunks, foxes, etc.

• Lyme disease -field mice, transferred by ticks

non-living reservoirs

• soil and water are most important

• Clostridium tetani is found in soil

  • tetanus

fomite

• any non-living object that spreads pathogens

  • ex.) used Kleenex, used syringe, surfaces

3 Principles of Disease Transmission

1. contact transmission

2. vehicle transmission

3. vector transmission

direct- contact (ex)

• person to person contact

  • Chlamydia, other STDs

indirect- contact

through fomites

droplet- contact

• spread a short distance (<1m)

  • ex.) coughing, sneezing, talking

    • inflenza

vehicle transmission

• pathogens of transmitted by a medium

what causes waterborne- vehicle

• due to improperly treated sewage

  • ex.) E. coli

airborne- vehicle

• spread >1m in droplets

  • ex.) Mycobacterium tuberculosis

foodborne- vehicle

• food poisoning

  • ex.) Salmonellosis

vector transmission

• animals that carry pathogens from one host to another

  • usually insects

examples- vector

• West Nile Virus: birds (reservoir) → mosquitoes → humans

  • Lyme disease: field mice → ticks → humans

healthcare associated iinfections (HAI)

• Nosocomial infections

• infection acquired in a hospital

• occurs in 5-10% of patients

result from several factors- HAI

• pathogens in the hospital

• immuno-compromised (weakened) state of patients

• chain of transmission

  • direct contact: staff to patient or patient to patient

  • indirect contact: through fomites

  • airborne: through ventilation systems

steps to controlling the spread of disease

1. hygiene

2. vectors and reservoirs

3. avoidance

4. isolation

proper hand washing

• single most effective way to combat spread of disease

others ways to control spread of disease- hygiene

• proper sterilization, disinfection, sanitization

• proper preparation of food, water

• proper sanitation, sewage treatment

vectors and reservoirs

• controlling insect vectors

  • mosquito control

• vaccination of domestic animals

  • against rabies

how to avoid contact with carriers

use of nitrile gloves

quarantine

• infected individuals removed from society

  • ex.) tuberculosis sanatoriums, Leper colonies, COVID-19

isolation

• people who are highly susceptible are isolated

  • bone marrow transplant patienta