epidemiology

epidemiology definition

the study of the incidence, distribution, and possible control of disease and other factors relating to health

rank the occurrence of disease from less frequent cases to most frequent cases

• epidemic

• emerging

• sporadic

• pandemic

• endemic

answer : sporadic , endemic , epidemic , pandemic , emerging

• sporadi : disease occurs only occasionally

  • example : botulism

• endemic : disease occurs at fairly consistent levels

  • common cold

• epidemic : disease occurs in unusually high numbers

  • influenza

• pandemic : disease spreads worldwide

  • covid-19

• emerging : newly identified with a notable number of cases

  • MERS, west nile virus

Chain of Infection

• reservoir

  • human

  • animal 

  • non-living

• source of infectious agents

• human reservoir

  • people can transmit pathogens without having any signs of disease

  • can be passed at any stage of disease

  • example : typhoid mary

• animal reservoir

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

  • influenza : birds → pigs → humans

• non-living reservoirs

  • soil and water

  • fomite : any non-living object that spreads pathogens

    • used tissue, doorknobs

contact transmission of disease

• direct : physical tough of person to person 

  • STDs ; pink eye

• indirect : through fomites

• droplet : spread short distances

  • coughing, sneezing, talking

Vector transmission of disease

• animals that carry pathogens from one host to another 

• usually insects (West Nile Virus) 

  • birds (reservoir) → mosquitos → humans

  • field mice → ticks → humans

Vehicle transmission of disease

• pathogens transmitted by a medium

• waterborne : E. coli - improperly treated sewage

• airborne : spread in >1m droplets

• foodborne : food poisoning

healthcare associated infections

• infections acquired while in a hospital

  • 5-10% of patients

  • up to 3 days after discharge

  • up to 30 days after surgery

• results from

  • pathogens in hospital

  • immunocompromised state of patients

• chain of transmission

  • direct : staff → patient / patient → patient

  • indirect : fomites

  • airborne : ventilation systems

4 methods to control the spread of disease

hygiene , control vectors/reservoirs , avoidance , isolation

1. hygiene

• proper hand-washing : single most effective way to combat spread of disease

• proper sterilization, disinfection, sanitization, and sewage treatment 

• proper food and water prep

2. control vectors and reservoirs

• controlling insect vectors : mosquito control

• vaccination of domestic animals against rabies 

• avoid vectors - repellant

3. avoidance

• avoid contact with carriers : using latex gloves

• quarantine : infected individuals removed from society

4. isolation 

• people who are highly susceptible are isolated

• bone marrow transplant patients are immuno-compromised