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Infectious epidemiology
Branch of epidemiology that deals with two or more populations at a time, cases are included as risk factors, and the cause of the disease is often known.
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Populations in infectious epidemiology
- Humans
- Infectious agents
- Vectors
- Animals
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Why is a case a risk factor?
Infection in one person can be transmitted to others.
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Uses for infectious epidemiology (5)
- Identify causes of new, emerging infections
- Study routes of transmission
- Surveillance of infectious disease
- Identify new interventions
- Identify source of outbreaks
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Influenza and pneumonia ranking for the leading causes of death in the US.
8th
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Infectious/parasitic infections account for what percentage of mortality worldwide.
20-25%
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Respiratory infections account for what percentage of mortality worldwide
7%
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Septecemia ranking for leading causes of death in the US.
10th
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Infectious disease
A disease caused by any of the infectious agents
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Communicable disease
Transmission of disease, directly or indirectly, from an infected person
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Transmissible disease
Disease transmission through unnatural routes from an infected person.
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Parasitic disease
An infection caused by a parasite
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An organism that lives on or in a host organism and gets it's food from or at the expense of the host.
Parasite
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Three major factors of the epidemiologic triangle.
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A factor, such as a microorganism, a chemical substance, or a form of radiation- whose presence, excessive presence, or relative absence is essential for the occurrence of disease.
Agent
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A person or other living animal, including birds and arthropods, that affords subsistence or lodgment to an infectious agent under natural conditions.
Host
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The domain in which disease-causing agents exist, survive, or originate.
Environment.
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The ability of an infectious agent to produce an infectous disease in an organism.
Pathogenicity
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Examples of infectious disease agents (6)
- bacteria
- rickettsia
- viruses
- fungi
- parasites
- prions
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The capacity of an agent to enter and multiply in a susceptible host and thus establish an infection.
Infectivity
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The severity of disease produced, i.e whether the disease has severe clinical manifestations or is fatal in a large number of cases.
Virulence
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Ability of an infectious agent to produce a toxin.
Toxigenicity
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Toxin
A toxic substance made by a living organism.
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Pathogens that cause disease as a result of their presence or activity within the normal, healthy host.
Primary pathogens
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Example of a primary pathogen
Influenza
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Organisms which cause an infectious disease in a host with depressed resistance.
Opportunistic pathogens
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Examples of opportunistic pathogens
Clostridium difficile
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Koch's Postulates
- The same organism is present in every case of the disease
- It is isolated or grown in pure culture
- The disease can be reproduced in animals after infection with pure culture
- The identical pathogen is reisolated from the experimental animals.
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The use of Koch's postulates in infectious epidemiology
They are one way to prove a disease is infectious.
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Host response characteristics
- Immunity
- Incubation period
- subclinical illness
- generation time
- carrier status
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Resistance to infection by an agent
Immunity
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Active immunity
Immunity that the host has developed either from natural infection with an agent or from injection of a vaccine containing an antigen.
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Active Immunity
Immunity acquired from natural infection
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Artificial Immunity
Immunity acquired from vaccination with an antigen
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Passive immunity
Immunity acquired from antibodies produced by another person or animal.
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Examples of passive immunity (2)
- Mother to fetus or newborn
- Injections containing antibodies
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The resistance of an entire community to an infectious agent as a result of the immunity of a large proportion of individuals in that community to the agent.
Herd immunity
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Percentage of the community that must be vaccinated before herd immunity comes into effect.
85%
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Time interval between invasion by an infectious agent and the appearance of the first signs or symptoms of the disease.
Incubation period
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Incubation period of influenza
1-3 days
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Incubation period of HIV
10 years
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An infection that does not show obvious clinical signs or symptoms. "inapparent infection"
Subclinical infection
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Time interval between lodgment of an infectious agent in a host and the maximal communicability of the host, precedes active symptoms.
Generation time
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A person or animal that harbors a specific infectious agent without discernible clinical disease and serves as a potential source of infection.
Carrier
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4 types of carriers
- Incubatory
- Active
- Convalescent
- Health/Passive
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Carrier that has been exposed to and harbors a pathogen, are in the beginning stages of disease showing very few symptoms, and can transmit the disease.
Incubatory
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Carrier that has been exposed to and harbor a disease causing organism.
Active
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Individuals who harbor a pathogen and are still infectious while in recovery
Convalescent
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Individuals who have been exposed to and harbor a pathogen but have not had any symptoms of disease
Healthy/Passive
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A parasitic nucleic acid, can contain RNA or DNA genome, can be enveloped or nonenveloped, has no cell.
Virus
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Prokaryotic organism with either gram positive or gram negative cell wall and can be aerobes, anaeorobes, or both.
Bacteria
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A eukaryotic organism, can be yeast or mold.
Fungi
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Unicellular, eukaryotic organisms with complex life cycles.
Protozoans
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Infectious protein particles that are viral in form and are composed completely of protein with no nucleic acid present.
Prions
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Large organisms (animals) with complex life cycles.
Worms
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The first case of a disease to come to the attention of authorities.
Index case
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Case
Person who has been diagnosed as having a disease, disorder, injury, or condition.
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First case of the disease in the population
Primary
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Those persons who become infected and ill from contact with the primary case
Secondary
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Persons infected by a secondary case
Tertiary
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A person who has been exposed but does not have any symptoms yet.
Suspect/Subclinical case
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Endemic
Refers to an infectious disease agent that is habitually present in an environment.
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Hyperendemic
Increase in endemic disease within a given area or group
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Health-related state or event in a defined population above the expected over a given time period
epidemic
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Epidemic affecting a large number of people, many countries, continents, or regions.
Pandemic
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Highly prevalent and commonly acquired early in life in most all of the children of a given population
Holoendemic
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A place where infectious agents normally live and muiltiply
Reservoir
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Two types of Human Reserviors
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Diseases associated with symptomatic human reservoirs
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Diseases associated with asymptomatic human reservoirs
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Three types of reservoirs
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Diseases with animal reservoirs
- Rabies
- Ebola
- West Nile Virus
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Two main environmental reservoirs
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Diseases with water reservoirs
Gastrointestinal diseases
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Organisms associated with soil as a reservoir
Clostridium botulinum
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Direct and esssentially immediate transfer of infectious agents to a receptive portal of entry though which a human or animal infection may take place.
Direct Transmission
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Transmission involving an intermediary source of infection such as a vehicle, droplet nuclei, or vectors.
Indirect transmission
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Site where an infectous agent enters the body.
Portal of Entry
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Site where the infectious agent leaves an infected persons body.
Portal of Exit
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Vehicle-borne infections
Result from contact with contaminated vehicles.
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Vehicles
Contaminated nonmoving objects.
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Fomite
An inanimate object that carries an infectious disease
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Typhoid Fever: Cause and transmisson
- S. typhi
- Foodborne
- fecal-oral route
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Salmonella enteritis: Cause and Transmission
- S. enteritidis
- Foodborne
- Fecal-oral
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Hepatitis C: Cause and Transmission
- Hepatitis C virus (HCV)
- Vehicle borne- contaminated needles or blood products
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Cholera: Cause and transmission
- Cause: Vibrio cholerae
- Water borne
- Fecal-oral
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Cryptosporidium parvum: Cause and transmission
- Parasite
- Water borne
- fecal-oral
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Mad Cow Disease (CJD): Cause and transmission
- prion
- foodborne zoonotic disease
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Botulism: cause and transmission
- Clostridium botulinum
- Food borne
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Campylobacter: Cause and transmission
- Bacteria
- Foodborne
- fecal-oral
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Shigellosis: Cause and transmission
- Shigella
- food borne
- fecal-oral
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Three Types of Anthrax
- Cutaneous
- Inhalation
- Gastrointestinal
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Fatality percentage of the three types of anthrax
- Cutaneous- 20%
- Inhalation- 95-100%
- GI- 25-100%
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Most common form of anthrax
Cutaneous
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Second most common form of anthrax.
Inhalation
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Airborne infections
Spread of droplet nuclei present in the air.
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Whooping cough: cause and transmission
- pertussis
- direct contact
- airborne (sneezing and coughing)
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Chicken pox: cause and transmission
- Varicella-zoster virus
- Direct contact
- airborne (sneezing and coughing)
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Inhalation anthrax: Cause and transmission
- Bacillus anthracis
- airborne
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Hantavirus: Cause and transmission
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Cutaneous anthrax: cause and transmission
- Bacillus anthracis
- direct contact (zoonotic)
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Vector-borne infections
Diseases transmitted by an animate, living insect or animal.
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Vectors
An arthropod, especially fleas and ticks.
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Mechanical transmission
Arthropod carries the pathogen on its feet
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Biological transmission
Pathogen reproduces in vector
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Lyme disease: cause and transmission
- Borrelia burgdorferi
- Vector borne (tick bite)
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Malaria: cause and transmission
- Plasmodium
- vector borne ( mosquito bite)
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Rabies: cause and transmission
- rabies virus
- vector borne (animal bite)
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Sexually transmitted diseases
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Gonorrhea: cause and transmission
- N. gonnorrheae
- Direct contact (sexual)
- Mother to fetus causes opthalmia neonatum
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Chlamydia: cause and transmission
- Chlamydia trachomatis
- Direct contact
- Mother to newborn causes pneumonia and conjunctivitis
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HIV/AIDS: cause and transmission
- HIV virus
- Vehicle- infected blood products or needles
- Direct contact- sexual contact
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Four stages of HIV
- Primary/Stage 1
- Asymptomatic/ Stage 2
- Symptomatic/ Stage 3
- HIV to AIDS/ Stage 4
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Stage of HIVwith short flu like illness.
stage 1/ primary
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Stage of HIV that lasts an average of 10 years, patient is free of symptoms, very low HIV levels in blood, detectable antibodies in blood.
Stage 2/ Asymptomatic
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Stage of HIV where symptoms are mild and there is an emergence of opportunistic infection
Stage 3/ symptomatic
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Stage of HIV where the immune system weeakens and illnesses become more severe
Stage 4/ HIV to AIDS
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Opportunistic infections with AIDS
- TB
- Kaposi sarcoma
- herpes
- Pneumocysis carinii
- Candida
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Vaccine preventable diseases, their causes and modes of transmission
- Diptheria- bacterial- direct contact
- Tetanus- clostridiuim tetani- vehicle borne
- Pertussis (Whooping cough)- pertussis- direct contact/airborne
- Hepatitis A and B- A- HAV, fecal-oral/foodborne
- B- HBV, vehicleborne
- Chicken Pox- varicella-zoster virus- direct contact
- Polio- poliovirus- foodborne
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Zoonisis
An infection or infectious agent transmissible under natural conditions from vertebrate animals to humans.
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Emerging infections
An infectious disease that has newly appeared or that has been known for some time but is rapidly increasing in incidence or geographic range.
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E. coli O157:H7 (emerging infection)
- Virulent E. coli strain
- Produces Shiga toxin
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Bioterrorism attack
The deliberate release of viruses, bacteria, or other germs used to cause illness or death in people, animals, or plants.
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Food borne hepatitis
A and E
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Blood borne hepatitis
B, C, D
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