Outbreak – (localized epidemic) – more cases of a particular disease than expected in a given area or among a specialized group of people over a particular period of time. Epidemic – large numbers of people over a wide geographic area affected. Cluster –an aggregation of cases over a particular period esp. cancer & birth defects closely grouped in time and space regardless of whether the number is more than the expected number. (often the expected number of cases is not known. ) pandemic -An epidemic occurring over a very wide area (several countries or continents) and usually affecting a large proportion of the population.
Risk – The probability that an individual will be affected by, or die from, an illness or injury within a stated time or age span. vector – an animate intermediary in the indirect transmission of an agent that carries the agent from a reservoir to a susceptible host. An organism that transmits the infection as a mosquito transmits the malaria protozoans. fomite – a physical object that serves to transmit an infectious agent from person to person. A comb infested with one or more head lice would be a fomite or the dust particles containing infectious cold virus that remain after droplets of infected saliva are coughed into the air.
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Zoonosis – An infectious disease that is transmissible from animals to humans. surveillance – The systematic, ongoing collection, analysis, interpretation, and dissemination of health data. The purpose of public health surveillance is to gain knowledge of the patterns of disease, injury, and other health problems in a community so that we can work toward controlling and preventing them. Scientific Method as related to Disease Detectives Compare Scientific Method to 10 Steps in Outbreak Investigation • Obtain.
Background Information (Steps 1- 3) Prepare for Field Work, Establish the Existence of an Outbreak – consider severity, potential for spread, public concern, and availability of resources, Verify the Diagnosis (commanality, verify procedure) • Define the Problem (Step 4-5) Define and Identify Cases – Case definition, identify cases(Confirmed, probable andpossible) and line listing, Describe and Orient the Data in Terms of Time, Place and Person – Descriptive Epidemiology • Formulate Hypothesis (Step 6)(Agent/host/environment triad) = chain of transmission • Develop a Study to Test the Hypothesis (Step 7).
• Collect Data and Observations (Step 7) • Evaluate Results (Step 7) • Determine if Hypothesis is true/modify (Step 8) • Formulate Conclusions (Step 9) • Report Results (Step 10) a. Cohort – Based upon exposure status whether or not they have outcome (illness); used with a small well-defined population and moves forward from exposure. Both groups have a known exposure and are checked for future outcomes or illness.
retrospective:(historic cohort) starts at exposure in past & moves forward to outcome prospective: starts a present exposure and moves forward in time to outcome (Calculations = attack rate and relative risk) Case-Control – Works backward from effect or illness to suspected cause. Control group is a selected group who has similar characteristics to the sick group but is not ill. They are then checked for similar exposures. It is often hard to select the control group for this type of study.
Odds Ratio is calculated to evaluate the possible agents & vehicles of transmission. Criteria to Draw Conclusions about Cause and Effect Relations: 1. Temporality – cause/exposure must precede effect/outcome 2. Consistency – observation of association must be repeatable in different populations at different times 3. Coherence, 1-1 relationship – exposure is always associated with outcome/ outcome is always caused by the specific exposure 4. Strength of association – relationship is clear and risk estimate is high 5.
Biological plausibility – biological explanation makes sense 6. Dose/response (biologic gradient) – increasing risk is associated with increasing exposure Incubation period – the time interval between initial infection and appearance of disease symptoms – followed by illness, then convalescence (recovery) Carrier – a person who does not show symptoms of a disease but can transmit a pathogen to others Reservoir (of infection) – any continual source of pathogens; may be human, animal, or nonliving Types of disease transmission.
1) Contact transmission – spread of disease in humans via some form of contact; three types: a) Direct (person-to-person) contact – transmission of pathogens by direct physicalcontact between two or more persons; touching, sexual contact, kissing; also includes transmission of disease via direct contact between animals and humans b) Indirect contact – transmission of a pathogen from its reservoir to a human via anonliving object (a fomite) c) Droplet transmission – spread of microbes in droplet nuclei (mucus droplets) over short distances (less than one meter) 2) Vehicle transmission – transmission of pathogens via a medium such as water, air, food,body fluids, and drugs.
Includes waterborne, foodborne, and airborne transmission. 3) Vector transmission – transmission of disease via animals that carry pathogens from host to host. Two types: a) Mechanical transmission – accidental or incidental transport of pathogens on the body parts of a vector b) Biological transmission – vector transmission in which the pathogen lives or grows in the body of the vector and is transmitted as the vector completes its life cycle 4) Vertical transmission – transmission from parent to offspring via sperm, ovum, placenta, or milk 5) Horizontal transmission – transmission from one person to another (excluding parent tochild) Portals of Entry:
Skin/Mucous Membranes – usually must be damaged for bacteria to penetrate GI Tract – organisms that enter via this portal must be able to withstand enzymes & extremes in pH Respiratory Tract – organisms enter via the nose and mouth during inhalation Urogenital Tract (Urinary/Reproductive Tracts) – often linked to spread of STDs and UTIs Parenteral route – entry into deep tissues or blood via injection, bites, wounds, or surgical procedures Centers for Disease Control and Prevention (CDC) * Morbidity: Incidence of a specific notifiable disease * Mortality: Deaths from notifiable diseases.
* Morbidity rate: Number of people affected in relation to the total population in a given time period * Mortality rate: Number of deaths from a disease in relation to the population in a given time Epidemiology The study of where and when diseases occur Nosocomial Infections Are acquired as a result of a hospital stay Affect 5–15% of all hospital patients Predisposing Factors * Make the body more susceptible to disease * Short urethra in females, climate, Fatigue, Age, Lifestyle, chemotherapy * Inherited traits, such as the sickle cell gene.