Ch 14: Principles of Disease and Epidemiology Flashcards
Why might different types of bacteria colonize different parts of the body?
- Nutrient availability
- Physical and chemical factors (temp and pH)
- Host defenses
- Mechanical factors (chewing, flushing, mucus, cilia)
What phylum of bacteria dominate the newborn gut?
Firmicutes
(ex: Genus Lactobacillus adapted to feeding on human milk)
What type of microbiota may be present in the host for days, weeks, or months, then disappear?
Transient microbiota
What are the locations of normal human microbiota? (7)
- Skin
- Eyes (conjunctiva)
- Nose, throat, and upper respiratory tract
- Mouth
- Large intestine
- Urinary tract
- Reproductive system
Why do most of the microbes in direct contact with skin not become residents?
- Sweat and oil glands have antimicrobial properties
- Keratin is a resistant barrier
- Low pH of the skin inhibits many microbes
- Skin has relatively low moisture
Although some normal microbiota are potential pathogens in the nose and upper respiratory tract, their ability to cause disease is reduced by? (2)
- Microbial antagonism
- Nasal secretions kill or inhibit many microbes, and mucus and ciliary action remove many microbes
What organ contains the largest number of resident microbiota?
Large intestines
(abundant moisture and nutrients)
What is microbial antagonism?
- Competitive exclusion
- Competitions between microbes, where normal microbiota protect the host from pathogenic microbes
What is the difference between prebiotics and probiotics?
- Prebiotics: chemicals and nutrients that selectively promote the growth of beneficial bacteria
- Probiotics: live microbes applied to or ingested into the body intended to exert a beneficial effect
What is the most common cause of Clostridium difficile infections? How can they be treated?
- Overuse of antibiotics
- Fecal transplant
What is commensalistic symbiosis?
One organism benefits while the other is unaffected
What is mutualistic symbiosos?
- Both organisms benefit
- Ex: E. coli synthesize vitamin K and some B vitamins
What is parasitism?
- One organism benefits at the expense of another, such as pathogens
Although our normal microbiota don’t typically cause disease, some of them can act as ______ which can cause disease
Opportunistic pathogens
What do Koch’s Postulates on the causation of diseases state? (4)
- The same pathogen must be present in every case of the disease
- The pathogen must be isolated from the diseased host and grown in pure culture
- The pathogen from the pure culture must cause the disease when it is inoculated into a healthy, susceptible lab animal (more than once)
- The pathogen must be isolated from the inoculated animal and must be shown to be the original pathogen
What are some problems with Koch’s Postulates?
- Some organisms cannot be cultured on artificial media
- Some disease types can be caused by multiple different pathogens
- Some pathogens cause multiple sieases
- Some carriers can be asymptomatic
- Some pathogens leave tell-tale signs that no other pathogen can produce (implicating disease without Koch’s postulates)
Why are the Bradford Hill criteria for the causation of disease better than Koch’s postulates? (3)
- More universal
- Generalized
- Not limited to infectious agents
Explain Bradford Hill’s criteria for causation.
- Strength: A likely cause associated with a larger effect
- Consistency: A likely cause is observed in different contexts
- Specificity: A likely cause is associated with a specific population and site
- Temporality: A likely cause occurs before the effect
- Biological gradient: Greater exposure to a likely cause leads to greater incidence
- Plausibility: A Liekly cause is typically a plausible one
- Coherence: Epidemiological and laboratory findings support each other in pointing out a likely cause
- Experiment: A likely cause would pass Koch’s tests
- Analogy: similar causes cause similar effects
What is a contagious disease?
- A disease that is easily spread from one host to another
- Does not require close contact and can occur through inanimate objects
What is a communicable disease?
- A disease that is spread from one host to another either directly or indirectly
- Requires close contact, fluid exchange, contaminated substances or sex
What is a noncommunicable disease?
- A disease that cannot be transmitted by human to human contact
- If it is an infectious agent, requires some kind of non-human host (i.e. mosquitoes)
Ebola, HIV/AIDS, and Hepatitis are all exaples of ____ diseases.
Communicable
Tetanus, food poisoning, Lyme disease, Malaria, and Zika are all examples of _____ diseases
Noncommunicable disease
Influenza, measles, common cold, and COVID-19 are examples of _____ diseases.
Contagious
What is the difference between incidence and prevalence?
- Incidence: the number of new cases of a disease over a specific time period; indicator of the spread of the disease
- Prevalence: the number of existing cases of a disease at a given time; includes both old and new cases; indicator of how seriously and how long a disease affects a population
Prevalence = ?
(incidence x time) - (deaths + cures)
Is measuring prevalence of a disease more useful for acute diseases like COVID-19 or chronic diseases like HIV/AIDS and cancer?
Chronic
What is herd immunity?
When enough people in a population are immune that other are protected from the spread of infection as a consequence
It is estimated that as many as ___% of people would need to be immune to disrupt the rapid transmission of SARS-CoV-2.
94%
How many people would have to die before herd immunity is reached naturally for SARS-CoV-2?
Tens of millions
What is a focal infection?
An infection that began as an asymptomatic infection in one place, causes distant injury, and damage to another part of the body.
What is the difference between bacteremia and septicemia?
- Bacteremia: presence of bacteria in the blood; not necessarily pathogenic
- Septicemia: growth of bacteria in the blood
What virus causes a viremia?
Polio (essential for its pathogenesis)
Among unvaccinated individuals, _____% of cases of SARS-CoV-2 infections are asymptomatic.
20-40%
The main problem of rapid spread
What is the case fatality rate of COVID-19?
2% (1.5-9.8%)
What was the case fatality of the Spanish flu of 1918?
10-20%
What is the case fatality rate of prion disease?
100%
What is the case fatality rate of untreated AIDS?
80-90%
What is the incubation periord of a disease?
- Interval between infection and signs or symptoms
- Able to spread infection
What is the prodromal period of a disease?
- Early stage of a disease
- Mild symptoms (fever, rash, etc)
What is the period of illness of a disease?
- Most severe part of the disease
- WBCs go up or down
- Death is possible
What is the period of decline of a disease?
- Improvement of disease
- Vulnerable to secondary infections
- Still capable of spread
What is the period of convalescence?
- Return to normal health
- Spread of infection is still possible depending on the agent
How long is the incubation period of SARS-CoV-2?
4-14 days
What symptoms are present in the prodromal period of SARS-CoV-2 infection?
- Fever
- Loss of taste/smell
- Headache
What symptoms are present in the period of illness of SARS-CoV-2 infection?
- Respiratory distress
- ICU admission
- Possible death
What are reservoirs of infection?
- Continual source of infection
- Pathogen has resources for survival and opportunity for transmission
- May be living or non-living
What are the 3 types of contact transmission?
- Direct: requires close association between infected and susceptible host
- Indirect: spread by non-living objects
- Droplet: transmission by proximity to large infectious agent containing droplet less than 1 meter away
What is the upper limit for air-borne droplets?
100 microns
What is the upper limit for droplets to enter deeply into the lungs?
5 microns
What are the 3 main methoids of vehicle transmission of a disease?
- Waterborne (i.e Cholera)
- Foodborne (i.e Salmonella)
- Airborne (i.e fungi from dust)
What are zoonoses?
Diseases transmitted by animals to humans
Ex: Influenza, Covid, etc.
What arthropods are common vectors for disease?
- Fleas
- Ticks
- Mosquitoes
5-15% of all hospital patients acquire ____ infections. 8th leading cause of death in the US
Nosocomial infections
Why are nosocomial infections so problematic?
- Often antibiotic-resistant due to the environment they are located
- Resistant organisms become part of the normal microbiota of hospital staff and patients
Which procedure has the highest likelihood of causing a nosocomial infection?
IV catheter
What is descriptive epidemiology?
- Collection and analysis of data
- Done retrospectively or prospectively
- Ex: Snow and the London Cholera epidemic of 1854
What is analytical epidemiology? Subtypes?
- Comparison of a disease group and a healthy group
- Case-control method: compare those with and without
- Cohort method: comparisons of individuals by category
What is morbidity?
Incidence of a specific notifiable disease
What is mortality?
Deaths from notifiable diseases
