Chapter 10: Infectious disease
Foodborne illness
Bilogic agets of foodborne illness include bacteria, parasites, viruses, and prions linked to mad cow disease
Indirect transmission (person-person)
Direct and essentially immediate tranfer of infectious agents to a receptive protal of entry through which human or animal infection may take palce
Person to person (direct transmission)
Direct and essentially immediate transfer of infectious agents to a receptive portal of entry through which human or animal infection may take place
Utility of performing out break investigation
- Has a goal of determining a cause of outbreak eliminating or interrupting transmission, and providing post-exposure prophylaxis. -Uncovers new infectious agents and diseases -Identifies spread of unknown virus to a new geographic area. -Improves epidemiological understanding by uncovering new means of disease transmission - Leads to public health regulations/ recommendations to prevent future disease outbreaks
Examples of signicifant Infectious diseases
- Sexually transmitted diseases - Foodborne diseases - Waterborne diseases - Vector-borne diseases -Vaccine preventable diseases -Zoonotic diseases - Emerging infections - Bioterrorism-related diseases
Point source epidemic
-A type of common source epidemic that occurs when the exposure is brief and essentially simulatneous, and the resultant cases all develop within one incubation period of the disease -Usually for a brief period
Conditions of an outbreak
-Agent and susceptible hosts are present in sufficient numbers -The agent can effectively be conveyed from a source to susceptible hosts
Exmaples of bacterial agents included
-Campylobacter -Clostridium botulinum -Salmonella -Escherichia Colio - Listeria Monocytogenes -Staphylococcus aureus
Common source epidemic
-Outbreak due to exposure of a group of persons to an noxious influence that is common to the individuals in the group - All susceptible individuals have a common exposure -Indirect transmission most likely chape of epidemic curve -Fewest number of cases before the min incubation period MIdline of the curve define the usual incubation period Uni-modal shape typical -Prolonged exposure to source of outbreak widens the apex of the common source curve
Goals of an outbreak investigation
-Rapidly identify the source and reservior of the outbreak - Implement interventions to control and eliminate the outbreak -Develope policies to prevent future outbreaks
Methods of outbreak Investigation
1) Identify the problem 2) Appraise the data 3) Formulate the hypothesis 4)Confirm the hypothesis 5) Draw conclusions and formulate practical application
Infectious
A disease due to an infectious agent. Ex: Bacteria and viruses
Contagious
A disease transmitted by direct or indirect contact with a host that is the source of the pathogenic agent
Agent
A factor(microorganism, chemical substance, or form of radiation) whose presence, excessive presence, or deficiency diseases) relative absence is essential for the occurence of a disease
Epidemic curve
A graphic plotting of the disctribution of cases by time of onset. May reflect a common source epidemic or a point -source epidemic
Carrier
A person or animal that harbors a specific infectious agent without discemible clinical disease, and that serves as a potential source of infection
Carrier
A person or animal that harbors a specific infectous agent without discernible clinical disease, and that serves as a potential soure of infection
Host
A person or other living animal, including birds and arthropods, that affords subsistence or lodgement to an infectious agent under natural conditions.
Reservior (2)
A place where infectious agents normally live and mulitply
Reservior
A place where infectious agents normally live and multiply. Can be human beings,animals, insects,soils, or plants
Antigen
A substance that stimulates antibody formation usually for long duration (measured in years)
Infectious Disease Agents
Agents include specific microbes and vectors involved in the cycle of disease tranmission. Ex: Bacteria,viruses,fungi,parasites
Sexually transmitted diseases
Also called sexually tranmitted infectons
Vector
An animate living insect or animal that is involved with the transmission of disease agents transmission of an infectious disease agent may happen when the vector feeds on a susceptible host
Communicable
An illness due to a specific infectious agent or its toxic products that arises through transmission of that agent or products from an infected person, animal, or reservoir to as susceptible host, either directly or indirectly through an intermediate plant or animal host, vector, or the inamimate enviornment.
Fomite
An inanimate object that carriers infectious disease agents
Parasitic Disease
An infection caused by a parasite, which is an anmial or vegetable organism that lives on or in another and derives its nourshiment.
Subclinical Infection
An infection that does not show obvious clinical sights or symptoms also called an inapparent infection.
Subclinical Infection (2)
An infection that does not show obvious clinical signs or symptoms also called an inapparent infection
Zoonosis (2)
An infections or infections agent transmissible under natural conditions from vertebrate animals to humans
Zoonosis
An infectious agents transmissible under natural conditions from vertebrate aimals to humans
Emerging Infectious Diseases
An infectious disease that has newly apeared in a population or that has been know for some ime but is rapidly increasing in incidence or geogrpahic range.
Vector borne diseases
Bacterial disease -Lyme diseases Arthropod-borne -Eastern equine encephalitia Parasitic diseases -Malaria
Retrospective cohort design
CLassify persons on the basis of exposure to the suspected source of infection
Case control design
Classify persons on the basis of infectious status - Cases have evidence of infection -COntrols have no evidende of infection
Vaccine- preventable diseases
Conditions that can be prevented by vaccination
Herd Immunity
Disease agent must be restricted to a single host species, and transmission must be relatively direct from one member of host species to another.
Zoonotic Diseases
Diseases transmitted from vertebrate animals to human beings Ex: Rabies
Portal of exit
For an infected person, a portal of exit is the site from which the agent leaves that persons body
Passive Immunity
Immunity acquired from antibodies produced by another person or animal
Incubation period
In conjunction with info about symptoms provides clues to possible infectious disease agents
Factors related to host response
Incubation period Subslinical illness Generation time Carrier Status
Vehicle -borne infections
Infections that result from contact with vehicles, which are contaminated,non moving objects
Airborne Infections
Involve the spread of droplet nuclei (particles) that are present in the air
Indirect transmission (2)
Involves intermediary sources of infections such as vehicled, droplet nuclei (particles) and vectors.
Indirect transmission (2)
Involves internediary sources of infectious such as vehicles, droplet nuclei (particles) and vecters.
The epidemiologic Triangle
One of the long standing models used to describe the etiology of infectious diseases. Includes 3 major factors. They are agent, host and enviornment
Direct transmission
Person to person
direct transmission
Person to person
Isolation
Persons who have a communicable disease are kept away from other persons for a period of time that corresponds generally to the interval when the disease is communcable, for example,maintaining isolation of patients with ebola in special isolation units.
Isolation
Persons who have a communicable disease are kept away from other persons for a period of time that corresponds generally to the interval when the disease is communicable
Quarantine
Persons who have been exposed to an infectious disease are prevented from interacting with those not exposed.
The external enviornment comprises these components
Physcial Climatologic Biologic Social Economic
The external enviornment comprises these components (2)
Physical Climatologic Biologic Social Economic
Endemic
Refers to an infectious disease agent that is habitually present in an enviornment
Portal of entry
Site where the agent enters the body
Toxin
Some infectious disease agents, instead of acting directly, produce a toxin that causes illness
Final steps in outbreak investigation: Case mapping
Some investigations may use computer software to show the location of cases.
Infectivity
The capacity of an agent to enter and muliply in a suspectible host and thus produce infection or disease.
Bioterrorism Attack
The delibrate release of virsues, bacteria, or other germs used to cause illness or death in people,animals, or plants.
Environment
The domain in which disease causing agents may exist, survive, or orginate
Immunity
The hosts ability to result infection by the agent. Active or passive. Active Immunity. Immunity that the host has developed as a result of natural infection with a microbial agent. Can be acquired from an injection of a vaccine that contains an antigen.
Clinical Observations
The pattern of symptoms suggests possible infecious agents Possible symptoms of an outbreak
Portal exit
The site from which the agent leaves that persons body
Generation time
The time interval between lodgment of an infectious agent in a host and the maximal communicabiity of the host.
Generation Time
The time interval between lodgment of an infectious agent without discemible clinical disease, and that serves as a potential source of infection.
Incubation Period (2)
Time interval between invasion by an infectious agent and the aperance of the first sign or symptom of the disease.
Incubation Period
Time interval between invasion by an infectious agent and the apperance of the first sigh or symptom of the disease.
Attack rate
Used frequently to describe the occurence of foodborne illness, infectious diseases, and other acute epidemics
Index Case
Used in an epidemiciologic investigation of a disease outbreak to denote the first case of a disease to come to the attention of authorites
Index Case
Used in epidemiology to denote the first case of a disease to come to the attention of authorities.
Hypothesis
Using the info that has been gatheres, the epidemiologist nay formulate a hyothesis regarding the causative agenPlan for the prevention of future outbreaks.
Indirect transmission
Vehicle-borne infections Airborn infections Vector-borne infections
Indirect transmission
Vehicle-borne infections Airborne infections Vectors-borne infections
Quaratine
Well persons who have been exposed to an infectious disease are prevented from interacting with those not exposed for example,preventing medical personnel who have been exposed to ebola virus from leaving their place of residence. This is diffrent from isolation.
Virulence
Wheather the disease has severe clinical manifestations or is fatal in a large number of cases