epidemiology

epidemiology definition

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

occurence of disease

• sporadic

• endemic

• epidemic

• pandemic

• emerging

• disease occurs only occasionally

  • example : botulism

• disease occurs at fairly consistent levels

  • common cold

• disease occurs in unusually high numbers

  • influenza

• disease spreads worldwide

  • covid-19

• 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

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 

2. avoidance

3. isolation