Lecture 20- Epidemiology Flashcards
Non-communicable diseases
Diseases that don’t spread from one host to another. Microorganisms arise from the individuals own normal microbiota or from the environment
Attack rate
The proportion of people who become ill in a population after exposure to an infectious agent.
100 people eat chicken contaminated with salmonella and 10 people develop the symptoms. What is the attack rate?
10%
Incidence of a disease
Number of NEW cases in a specific time period in a given population.
Measures the risk of an individual contracting the disease
Prevalence of a disease
The total number of cases at any time or for a specific period in a given population
Reflects the overall impact of a disease on society (includes old and new cases)
Morbidity
Illness
Rate of the incidence of disease in a given population
Contagious diseases have high morbidity rates because they cause illness to spread
Mortality
The number of people in a defined pop. who die during a given period.
Case-fatality rate
Proportion of persons diagnosed with a specific disease who die from that disease.
Ebola- high case fatality rate
Endemic
Diseases constantly present in a given pop
Sporadic
Diseases that occur from time to time
Epidemic
Unusually large number of cases in a pop
Outbreak
A group of cases occurring during a brief time interval and affecting a specific pop.
Can signal the onset of an epidemic.
Pandemic
An epidemic that spreads over several continents
Chain of infection
Source/reservoir of an infectious agent
Agent must leave source through portal of exit
Transmitted to a new host
Colonize the new host or enter that host through a portal of entry
Susceptible host
Why is the chain of infection important?
Allows researchers and public health workers to determine where links in the chain can be broken. This stops or slows the spread of the infection.
Reservoir of infection
Pathogen needs suitable environment (natural habitat)
Can be in an animal (ex human) or in the environment (soil and water)
Plague - wild rats squirrels and prairie dogs
Now these reservoirs are controlled
Human only reservoirs
Easier to eradicate cause you can prevent and control in humans. Harder to control and prevent in wild animals.
Ex smallpox
Asymptomatic infection
Person that has the pathogen but no symptoms.
Makes it harder to control the disease
STDs
Usually low dose of infection microorganisms are Asymptomatic because there needs to be a certain amount until symptoms appear, and multiplying takes time.
Zoonotic diseases
Transmitted to humans but primarily exist in other animals
More severe in humans than in other animals because the infection in humans is accidental. No evolution towards the balanced pathogenicity between host and parasite.
Environmental reservoirs
Difficult or impossible to eliminate.
Clostridium botulinum and tetani
Portals of exit
Intestinal tract microorganisms: shed in the feces.
Contaminated drinking water and food.
Respiratory viruses: exit body in droplets of saliva and mucus when people talk, laugh, sing, sneeze, or cough
Skin; staphylococcus aereus uses skin as a portal so then leave the host when the skin sheds
Genital pathogens: carried in semen and vagina secretions (chlamydia)
Eyes
Transmission
Vertical transmission: mother to child during childbirth or breastfeeding
Horizontal transmission: all other types; person to person, person to environment, direct or indirect transmission.
Direct transmission
Immediate transfer
Physical contact: touching, kissing, sex…usually low infectious dose microorganisms are spread this way…and microorganisms that can’t survive in the cold dry environment
Hand washing prevents
Droplet spread: spreads respiratory disease.
Common in heavily populated areas. Schools.
Prevention by making things farther apart: desks, beds (barracks)
Low infectious dose
Few microbial cells are needed to initiate infection
Indirect transmission: airborne
Through air
Airborne: common for smaller particles to cause disease this way.
Droplets, dead skin cells, household dust, soil in the wind can transmit airborne respiratory pathogens using the air.
Air conditioning promotes the spread
Ventilation systems help
Indirect transmission: fomites
via contaminated food, water, or inanimate objects. Mosquitoes, fleas, and ticks
Vehicles born: fomites (inanimate objects) foods and water transmit pathogens
Clothing, drinking glasses, cell phones.
Hand washing prevents this type
Foods; animal pathogens (poultry) and staphylococcus carriers handling food
Cross-contamination: pathogens from one food transferred to another.
Proper disinfecting, storage, and cooking prevents this
Vector borne: a living organism that can carry a disease causing microbe. Can carry it externally or internally. Flies, fleas, live, and ticks.
Mechanical vector: Flies carry shit and pass microorganism to food. Carries it onto its body from one place to another.
Biological vector: participates in the life cycle of a pathogen and provides a place for it to multiply. The pathogen is harbored internally in the vector (mosquito) and is injected into host.
Portals of entry
Inhaling a microbe: nose is the portal of entry
Intestinal pathogen have to be ingested so mouth is the portal of entry.
Fecal Oral transmission: fecal organisms that are injested
If you take a vaccine, are you guaranteed to not get the disease?
No, gaining a large dose of the pathogen can produce serious disease in a vaccinated person. So they have to be careful.
The incubation period
The longer the incubation, the faster it spreads, because if symptoms don’t appear people won’t prevent themselves from infecting others.
Herd immunity
If 90% of the population is immune to the disease then the disease is unlikely to spread.
This is due to herd immunity.
Herd immunity protects non immune individuals when an infectious agent cannot spread in a pop. because most potential hosts are immune.
Infectious agents that undergo antigenic variation overcome herd immunity.
What increases people’s chances of getting the illness?
Malnutrition, overcrowding, fatigue Improper food or sanitation. Young or very old age Female contract UTIs more Not cooking thoroughly Not breastfeeding (breastfeeding provides antibodies against microorganisms)
When an infection occurs in a healthy individual, it is more likely to be Asymptomatic.
Environmental factors that influences the epidemiology of disease.
Temp, water and nutrient supply, radiation, availability of light and oxygen.
Endospore forming organisms survive better
Antibiotics get rid of susceptible organisms and leave the resistant ones to multiply with less competition
John snow
Illustrated the power of a well designed epidemiological study. Found the reason for the cholera epidemics. Compared the water supply of infected households to non infected households. Found that the infected households had contaminated water
Descriptive studies
Collect data that characterize the occurrence; type of population infected, location of infected people (gives clue about reservoir of infectious agent and vectors), timing (uses epidemic curve to determine incubation period)
This information is used to compile a list of possible risk factors involved in the spread of disease.
Propagated epidemic
Shows timing of contagious disease
Uses gap between index case (first case) and new cases to determine incubation period
Common source epidemic
When patients are all exposed to a single source of the infectious agent. Contaminated food is an ex. Shows rapid rise in the numbers of people
Seasonal occurrences: influenza and common cold (crowded indoor conditions during the winter), warm weather (mosquitos, ticks, eat picnic food that hasn’t been stored properly) m
Analytical studies
Determines which potential risk factors identified by the descriptive studies are actually relevant in spreading the disease.
Case control studies, cross sectional studies, and cohort studies
Case controlled studies
Starts with the disease and attempts to determine the chain of events leading to it. Works backwards.
Controls must be equal to the case (age, gender, socioeconomic status)
Cross sectional study
Gather information about possible risk factors and the occurrence of disease at one point in time
Doesn’t attempt to establish cause of disease
Cohort studies
Follow groups with specific risk factors into the future to see if disease develops
Attempts to find the cause.
More time consuming and expensive
Experiments studies
Used to judge the cause and effect relationship of the risk factors (preventative factors) and the development of disease.
Assess the value of a particular intervention or treatment such as antimicrobial drug therapy.
Compared with a placebo. Double blind eliminates bias - researchers and subjects don’t know whether they receive the placebo or the real treatment.
Infectious disease surveillance
Recognizing and reporting disease cases to public health authorities. Provides clues to the cause of the disease
Cooperative surveillance efforts coupled with global immunization programs and isolation of cases can result in eradication of disease.
National disease surveillance network
Communicable diseases
Contagious (transmitted from one host to another)
Direct/indirect: kiss/drinking an infected persons glass
Centers for disease control and prevention
Provides support for infectious disease laboratories in the US and publishes the Morbidity and Mortality Weekly Report.
Notifiable diseases in report: diseases that are relatively high incidence or pose potential danger to public health
Dispatches teams worldwide to assist with identifying and controlling epidemics
Public health departments
Each state has a state epidemiologist who oversees a network of public health laboratories involved in infection surveillance and control.
Also includes public schools (absentee rates) and hospital laboratories (isolation of pathogens with epidemiological significance)
World Health Organization
Agency of the UN that is devoted to achieving the highest possible level of health around the globe.
Provides worldwide guidance in the field of health, sets global standards for health, coo
How to reduce or eradicate diseases
sanitation, reservoir and vector control (natural habitat and flea), vaccination, and antibiotic treatment
What are emerging diseases, and what contributes to them
New or recently increasing in incidence after a decline.
Microbial evolution; new serotypes and antibiotic resistance
Complacency + public health efforts; less concern after a decline, causes less news reports, education, research money, and social welfare (causes it to reemerge)
Changes in human society; daycares are common now and kids can share more diseases easier than before
Advances in technology; contact lenses; new place for microorganisms to live
Population expansion; contact with more reservoirs
Development; dams
Mass production, widespread distribution, and importation of food; food-borne illnesses
War and civil unrest; refugee camps (crowded and poor sanitation), destruction of buildings that prevent or research diseases
Climate changes; warm temps favors vector survival
Healthcare associated infections
Nursing homes (catheter, UTI), therapy centers,
Nosocomial infections (hospital acquired); extensive use of antimicrobial drugs and invasive therapeutic procedures has raised the incidence of HAI.
Many come from normal microbiota
Reservoirs of infectious agents in healthcare settings
Other patients, healthcare environments (P. aeruginosa gram negative rod that thrives in soap, disinfectants, toilets and sinks), healthcare workers (staph aureus, strept pyogenes), patient microbiota (surgery causes staph epi to enter bloodstream and cause bacteremia, reemergence of latent infections in cancer patients)
Transmission of infectious agents in healthcare settings
Diagnostic and therapeutic procedures (inadequately sterilized instruments/medical devices…catheter, respirator, IV, surgery)
Patient to patient transmission by healthcare worker
Bubonic plague
flea transmits Y. pestis from a rodent to a human, carried to lymph node, bubo (swelling) occurs within days, interferes with immune response
no person to person transmission
Septicemic plague
multiplying bacteria spill into bloodstream and cause a systemic inflammation
Causes shock and DIC
Pneumonic plague
person to person transmission (spreads to lungs and then is transmitted by respiratory droplets, 100% mortality rate if untreated
