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