Chapter Eight

Steps in the Investigation of an Infectious Disease Outbreak

(1) Define the problem (2) Appraise existing data (3) Formulate a Hypothesis (4) Confirm the Hypothesis (5) Draw conclusions and formulate practical applications

Third factor of the Epi Triangle

Agent: a factor such as a microorganism, chemical substance or form of radiation - whose presence or absence is essential for the occurrence of a disease.

Droplet Nuclei

Airborne infections; some venues for the airborne transmission of disease agents are closed, poorly ventilated environments; movie theatres, examination rooms, classrooms, and motor vehicles

Second Step in the Investigation of an Infectious Disease Outbreak

Appraise existing data: case identification - track down all cases implicated in the outbreak. clinical observations-record the pattern of symptoms and collect specimens. Tabulations and spot maps: plot the epidemic curve; calculate the incubation period; calculate attack rates; map the cases

Foodborne Illness

Botulism

First Step in the Investigation of an Infectious Disease Outbreak

Define the problem: verify that an outbreak has occurred; is this a group of related cases that are part of an outbreak or a single sporadic case

One factor of the Epi Triangle

Environment: the domain in which disease-causing agents may exist, survive or originate; it consists of "all that which is external to the individual human host."

Sexually Transmitted Disease

HIV/AIDS; Gonococcal Infections; Chlamydia Genital Infections

Second factor of the Epi Triangle

Host: a person or other living animal including birds and arthropods, that affords subsistence or lodgement to an infectious agent under natural conditions

Confirm the Hypothesis

Identify additional cases; conduct laboratory assays to verify causal agent.

Vector-borne Diseases

Lyme disease

Environment Components

Physical environment; climatologic, biologic, social and economic components

Zoonotic Disease

Rabies; Anthrax; Avian Influenza (bird flu); Hantavirus pulmonary syndrome (rodents); Toxoplasmosis (cats); Tularemia (rabbit fever); Creutzfeldt-Jakob disease (mad cow disease)

Carrier

a person or animal that harbors a specific infectious agent without discernible clinical disease and which serves as a potential source of infection. Ex: Typhoid Mary

Reservoir

a place where infectious agents normally live and multiply; the reservoir can be human beings, animals, insects, soil or plants

Attack Rate

a type of incidence rate used when the occurrence of disease among a population at risk increases greatly over a short period of time, often related to a specific exposure. Ill/(ill +well)

Vector

an animate, living insect or animal that is involved with the transmission of disease agents. Ex: arthropods, rodents

Infectious Disease (Communicable Disease)

an illness due to a specific infectious agent or its toxic products that arises through transmission of that agent or its products from an infected person, animal or reservoir to a susceptible host, either directly or indirectly through an intermediate plant or animal host, vector or the inanimate environment.

Fomites

an inanimate object that carries infectious disease agents. Ex: doorknobs, used towels

Parasitic Disease

an infection caused by a parasite, which is an organism that lives on or in a host organism and gets its food from or at the expense of its host.

Zoonosis

an infection or infectious agent transmissible under natural condition from vertebrate animals to humans

Emerging Infectious Disease

an infectious disease that has newly appeared in a population or that has been known for some time but is rapidly increasing in incidence or geographic range. Ex: HIV infection, Ebola virus disease, Hepatitis C, Avian Influenza and E.coli

Vaccine preventable diseases

are conditions that can be prevented by vaccination (immunization), a procedure in which a vaccine is injected into the body.

Formulate a Hypothesis

based on a data review, what caused the outbreak?

Active Immunity

can be acquired from an injection of a vaccine that contains an antigen ( a substance that stimulates antibody formation). A. immunity is usually of long duration and is measured in years.

Vehicles

contaminated, nonmoving objects which can include fomites, unsanitary foods, impure water or infectious bodily fluids

Herd Immunity

denotes 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.

Incubation Period

denotes the time interval between invasion by an infectious agent and the appearance of the first signs and symptoms of the disease

Indirect Transmission

intermediary sources of infection such as vehicles, droplet nuclei, and vectors

Index Case

is used in an epidemiologic investigation of a disease outbreak to denote the first case of a disease to come to the attention of authorities

Epidemiologic Triangle

one of the long standing models used to describe the etiology of infectious diseases. Environment; Agent; Host

Direct Transmission

refers to direct and essentially immediate transfer of infectious agents to a receptive portal of entry through which human or animal infection may take place. Ex: touching, kissing, biting, sexual intercourse, droplet spray

Passive Immunity

refers to immunity that is acquired from antibodies produced by another person or animal. Short duration, lasting from a few days to several months

Infectivity

refers to the capacity of an agent to enter and multiply in a susceptible host and thus produce infection or disease.

Immunity

refers to the host's ability to resist infection by the agent

Virulence

refers to the severity of the disease produced

Portal of Entry

site where the agent enters the body. Ex: respiratory system, skin wound, mucus membrane-nose, mouth, lungs

Bioterrorism Attack

the deliberate release of viruses, bacteria, or other germs (agents) used to cause illness or death in people, animals or plants

Subclinical (Inapparent)

the infection does not show obvious clinical signs and symptoms Ex: Hepatitis A Inapparent infections are epidemiologically significant and part of the spectrum of infection

Portal of Exit

the site from which the agent leaves the person's body. Ex: respiratory passages, the alimentary canal, the genitourinary system and skin lesions

Generation Tim

the time interval between lodgement of an infectious agent in a host and the maximal communicability of the host

Toxin

usually refers to a toxic substance (a material that is harmful to biologic systems) made by living organisms

Draw conclusions and formulate practical applications

what can be done to prevent similar outbreaks in the future?