Principles of Disease and Epidemiology Flashcards
Nosocomial Disease
can also be called a HAI a disease that is contracted in a healthcare facility.
Pathology
Study of disease
Pathogen
Pathogenic agents have special properties that allow them to invade the human body or produce toxins
Etiology
the study of the cause of a disease
Infection
invasion and growth of pathogens in the body
Disease
Abnormal state in which the body is not functioning normally.
ex. infectious agent overcomes body’s defenses
Pathogenesis
The development of disease
What is the protective role of normal microbiota?
- Prevent pathogens from attaching
- Consume available nutrients
- Produce toxic compounds that inhibit other microbes
Microbial Antagonism
- When established cultures of microorganisms prevent the intrusion of foreign strains. When introduced to an already-colonized environment, an invasive strain of bacteria tends not to thrive and may go completely extinct.
- Microbial antagonism is due to competition between microbes.
Resident flora
- Normal microbiota (acquired at passage through birth canal)
- Establish permanent colonies on/inside body without producing disease. Protect the host by
1. Occupying niches that pathogens might occupy (Competitive exclusion)
2. Producing acids
3. Producing bacteriocins
4. Stimulation of immune system
Transient Microbiota (Flora
Certain microbes are present for various periods (days, weeks, or months) – then disappears.
Probiotics
Live microbes applied to or ingested into the body, intended to exert a beneficial effect
Describe the dynamic nature of resident flora
changes due to age, type of food consumed, Hormonal state, antibiotics
Various Co-existance (symbiotic) Relationships Between Bacteria and Host
- Commensalism
- Mutualism
- Parasitism
Commensalism
One organism benefits and the other is unaffected
Mutualism
Both organisms benefit
Parasitism
one organism benefits at the expense of another
Symbiosis
relationship between 2 organisms in which at least one organism is dependent on the other
Opportunistic pathogens
cause disease under special conditions (mutualistic relationship becomes parasitic)
Healthy carriers of pathogenic organisms
An asymptomatic carrier (healthy carrier or just carrier) is a person or other organism that has contracted an infectious disease, but who displays no symptoms. Although unaffected by the disease themselves, carriers can transmit it to others.
How do microbes cooperate with each other?
One microorganism may make it possible for another to cause disease or produce more severe symptoms
Koch’s Postulates
provide proof of etiology of infectious disease
What are Koch’s postulates?
- 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
- The pathogen must be isolated from the inoculated animal and must be shown to be the original microbe
Key concepts of Koch’s postulates
- according to koch’s postulates, a specific infectious disease is caused by a specific microbe
- Koch’s postulates help determine the etiology of disease, the first step in treatment and prevention
- Microbiologists use these steps to identify the causes of emerging diseases
What are the exceptions to Koch’s postulates?
These exceptions made it necessary to modify Koch’s postulates:
- to establish disease etiology for viruses and certain bacteria, which cannot be grown on artificial media
- Some diseases, e.g.: pneumonia, meningitis, and nephritis, may be caused by a variety of microbes.
- Some pathogens, such as S. progenies, cause several different diseases.
- Certain pathogens, such as HIV, cause disease in humans only.
How are infectious diseases classified?
- Communicable
- Non-communicable
- Contagious
Symptom
A change in body function that is felt by a patient as a result of disease. Symptoms are subjective
Sign
A change in a body that can be measured or observed as a result of disease. Signs are objective
Syndrome
A specific group of signs and symptoms that accompany a disease
Communicable Disease
A disease that is spread from one host to another (genital herpes, TB)
Non-communicable Disease
A disease that is not transmitted from one host to another (tetanus, ulcers)
Contagious Disease
A disease that is easily spread from one host to another (common cold, chickenpox)
Incidence
Fraction of a population that contracts a disease during a specific time (new cases)
Prevalence
Fraction of a population having a specific disease at a given time
Sporadic disease
Disease that occurs occasionally in a population
Endemic disease
Disease constantly present in a population
Epidemic disease
Disease acquired by many hosts in a given area in a short time
Pandemic disease
Worldwide epidemic
How is the severity or duration of a disease described?
- Acute
- Chronic
- Subacute
- Latent
Acute
Disease develops rapidly
Chronic
Disease develops slowly
Subacute
Symptoms between acute and chronic
Latent
Disease with a period of no symptoms when the causative agent is inactive (TB, shingles)
Herd Immunity
Presence of immunity to a disease in most of the population
Local
limited to small area of body
Systemic
spread throughout body via blood or lymph
Focal
spread from local infection to specific areas of body
Primary
acute infection causing initial illness
Secondary
occurs after host is weakened from primary infection
Opportunistic infection after a primary (predisposing) infection
ex. Taking antibiotics for a primary infection will kill beneficial bacteria in the vagina, this allows yeast cells to grow uncontrolled; this causes a yeast infection.
Sepsis
Toxic inflammatory condition arising from spread of microbes or their toxins, from a focus
Bacteremia
Bacteria in the blood
Septicemia
Multiplication of bacteria in the blood
Subclinical
(inapparent): no noticeable signs and symptoms
Toxemia
Toxins in the blood
Viremia
Viruses in the blood
What are some factors that vary among people that make them susceptible to disease?
- Genetics
- Gender
- Climate and weather
- Age
- Stress and fatigue
- Lifestyle
- Chemotherapy
What are the stages of disease development?
- Incubation period
- Prodromal period
- Period of illness
- Period of decline
- Period of convalescence
Incubation period
Time interval between initial infection and first appearance of signs and symptoms.
Prodromal period
Characterized by appearance of first mild signs and symptoms.
Period of illness
Disease at its height: all disease signs and symptoms apparent.
Period of decline
Signs and symptoms subside
Period of convalescence
Body returns to pre-diseased state, health is restored.
During which stage(s) is a person contagious?
at all the stages of illness; it depends on the statistics of the disease.
Reservoir
continual source of infectious agents
What are the types of reservoirs?
- Nonliving: soil, contaminated water
- Human: people with disease or asymptomatic carriers with inapparent (subclinical) infections or latent diseases
- Animal: pathogen for some other species lives and multiplies in particular animal species.
Zoonosis
A type of disease that may be transmitted to humans from an infected animal.
How can disease be transmitted?
- Contact Transmission
- Airborne Transmission
- Vehicle Transmission
- Vector Transmission
What are the types of contact transmission?
- Direct: Close association between infected and susceptible host.
- Indirect: Spread by fomites.
- Droplet: Transmission via large (>10 µm) airborne droplets from saliva or mucus (coughing or sneezing)
Airborne Transmission
Pathogens carried on water droplets (
Vehicle Transmission
Water, food, air
Vector Transmission
Arthropods carry pathogens from one host to another (mechanical transmission vs. biological transmission)
What is the difference between mechanical transmission and biological transmission?
- Mechanical transmission – a vector such as a fly lands on soil or feces or trash and picks up pathogens on its feet, then deposits pathogens on food which are then swallowed by a host.
- Biological transmission – a vector such as a mosquito bites an infected person and ingests pathogens in the blood of that person, then bites another host and injects pathogens to the new host.
What is the difference between droplet and airborne transmission?
when the droplet is large (>10 micrometers) and in a short distance: Droplet transmission.When the droplet is small (
Nosocomial (Hospital-Acquired) Infections
- Acquired as a result of a hospital stay.
- 5-15% of hospital patients acquire nosocomial infections.
Aseptic techniques can prevent nosocomial infections. - Hospital infection control staff members are responsible for overseeing the proper cleaning, storage, and handling of equipment and supplies
VRE
- Vancomycin-resistant Enterococcus, or vancomycin-resistant enterococci, are bacterial strains of the genus Enterococcus that are resistant to the antibiotic vancomycin
- Becoming more prevalent
CRE
- CRE, which stands for carbapenem-resistant Enterobacteriaceae, are a family of germs that are difficult to treat because they have high levels of resistance to antibiotics. Klebsiella species and Escherichia coli (E. coli) are examples of Enterobacteriaceae, a normal part of the human gut bacteria, that can become carbapenem-resistant.
- Becoming more prevalent
HA
- hospital acquired
- USA100 and USA200
CA
- community acquired
- USA300 and USA400. Affect young and healthy. Associated with contact sports, sharing towels or athletic equipment, illegal iv drugs, and living in crowded or unsanitary areas (e.g., prisons, hurricane evacuee centers)
Emerging Infectious Diseases (EIDs)
Diseases that are new, increasing in incidence, or showing a potential to increase in the near future
CDC, NIH, and WHO
CDC, NIH, and WHO are responsible for surveillance and responses to emerging diseases
Contributing factors for EIDs
- Genetic recombination (E. coli 0157; H5N1 avian flu)
- Evolution of new strains (V. cholera 0139)
- Inappropriate use of antibiotics and pesticides (Antibiotic resistant strains)
- Changes in weather patterns (Hantavirus)
- Modern Transportation (West Nile virus)
- Ecological disaster, war, and expanding human settlement (Coccidioidomycosis)
- Animal control measures (Lyme disease)
- Public Health failure (Diphtheria)
- Improved case reporting
Epidemiology
The study of where and when diseases occur (disease transmission, incidence, and frequency)
What does the CDC do?
- Collects and analyzes epidemiological information in the United States
- Publishes Morbidity and Mortality Weekly Report (MMWR)
What does the WHO do?
Worldwide disease surveillance
John Snow
1848–1849; Mapped the occurrence of cholera in London
Ignaz Semmelweis
1846–1848; Showed that handwashing decreased the incidence of puerperal fever
Florence Nightingale
1858; Showed that improved sanitation decreased the incidence of epidemic typhus
Case reporting
Health care workers report specified diseases to local, state, and national offices
Nationally notifiable diseases
Physicians are required to report occurrence.
Morbidity
Incidence of a specific notifiable disease
Mortality
Deaths from notifiable diseases
Morbidity rate
Number of people affected in relation to total population in a given time period
Mortality rate
Number of deaths from a disease in relation to total population in a given time period.
