Lecture 14 Flashcards
Epidemiology
The study of the frequency and distribution of disease
Father of epidemiology
John snow famous for determining the cause of the 1854 cholera outbreak in London
Surveillance
Collecting, analyzing, and reporting data on rates of occurrence, mortality, morbidity and transmission of infections
Who does surveillance
In US CDC
Worldwide WHO
Prevalence
Accumulated total of existing cases with respect to the entire population
Prevalence formula
Total number of cases in population/ total number of persons in population
x100
Incidence
Number of new cases over a certain time period as compared with the general healthy population
Incidence formula
Number of new cases/ total number of susceptible persons
x100
Mortality rate
Total number of deaths in a population due to a certain disease
Mortality from infectious diseases have dropped over past century
Morbidity rate
Measures total number of persons afflicted with an infectious disease
Rate has remained high over past century
Endemic
An infectious disease that exhibits a relatively steady frequency over a long time period in a particular geographic locale
Endemic disease examples
Valley river in Southwestern US
Lyme disease in certain areas of the US like northeast
Sporadic
Infrequent or irregular cases of an infectious disease outbreak that occur randomly over a wide area
Sporadic disease examples
Measles and typhoid fever
Epidemic
An increased number of cases beyond expected levels that appear in geographic clusters
Epidemic examples
Syphilis and STDs
Foodborne
Influenza
Pandemic
The spread of an epidemic across continents
Pandemic examples
HIV/AIDS
COVID-19
Determining transmission
Ask about patient background
Locations frequented or traveled
Possible contacts
Habits
Food
Sexual partners
Transmission
Exchange of the pathogen from an infected individual to uninflected hosts
Direct transmission
Kissing, sex, biological vectors, large droplets
Indirect transmission
Airborne droplet nuclei, fomites, food
Reservoir
Primary habitat in the natural world from which a pathogen originates
Living reservoir
May or may not have symptoms, members of a host population or carriers, animals
Non-living reservoir
Soil and water for pathogenic fungi, bacterial endospores, parasite cysts ova and larvae
Asymptomatic carrier
Infected without symptoms, a living reservoir
Incubation, convalescent, and chronic carriers
Can transmit the infection either before or after the period of symptoms
Vectors
Live animal that transmits the infectious agent from one host to another
Biological vector
Actively participates in a pathogen’s life cycle, serving as a site for multiplication or completion of life cycle like anopheles mosquito
Mechanical vector
Not necessary to the life cycle of a pathogen only transports it without being infected like flies carrying bacteria
Zoonosis
Infection indigenous to animals but naturally transmissible to humans like west Nile and birds, human may be dead end host don’t contribute to persistence of microbe
Zoonoses
70% of all new emerging diseases worldwide
Common zoonotic infections
Rabies in mammals, west nile virus birds and mosquitoes, salmonellosis in chicken and swines, influenza in chicken and swine, anthrax in domestic farm animals
Nosocomial infections
Infectious diseases acquired or developed during a hospital stay, 0.1-20% of all admitted patients
CDC nosocomial infections
1.7 million each year
99,000 deaths per year
Common nosocomial infections
Urinary tract from catheters and being unable to stand, respiratory tract from breathing machines, surgical incision infections
Applying epidemiological info
Determine recommendations for individuals, determine recommendations for public health policy, predict future of disease, suggest ways to stop/slow disease spread
Etiological agent
Causative agent of infection or disease
Robert Koch
Laid foundation for determining the etiological agent for many infections and a standard for determining causation, developed pure culture methods, identified etiological agent of anthrax, TB, and cholera
Koch’s postulates
Show that a specific microorganism is responsible for a particular disease
Postulate 1
Correlate every case of disease with the presence of a certain microbe
Postulate 2
Isolate that microbe from an infected subject, cultivate it in a pure culture in the lab and identify it
Postulate 3
Inoculate a susceptible healthy subject with the laboratory isolate and observe the resultant disease
Postulate 4
Re-isolate the agent from this subject in Pure culture and prove its the same microbe that you inoculated
“Gold standard”
Koch’S postulates for identifying etiological agent of infections helped determine the cause of TB, diphtheria, and plague
Postulates don’t work for
Viral infections, obligate intracellular bacteria, microbes that cause multiple diseases
Modified for these pathogens
