Ch 15 - Disease & Epidemiology Flashcards
Epidemiology
The science that evaluates occurrence, determinants, distribution, and control of health and disease in a defined human.
John Snow
First epidemiologist
Studied cholera in London
Epidemiologists Determine
- Causative Agents
- Sources and/or reservoirs of disease agents
- Mechanisms of transmission
- Host and environmental factors that facilitate development of diseases within defined populations
- Control Measures
Measuring Infectious Frequency
To determine an outbreak, epidemic, or pandemic, epidemiologists measure disease frequency at a single time over time
Morbidity Rate Formula
Rate of new cases
(# new cases during specific time/total population size) x100%
Prevalence Rate Formula
Total number of cases
(# of cases in a population/total population size) x100%
Mortality Rate Formula
Rate of deaths
(# deaths due to specific disease/total population size with the disease) x100%
Factors in classifying infectious diseases
- Disease occurrence
- Disease severity/duration
- Host involvement
Incidence
The number of new people who develop a disease during a particular time period. Indicates how fast the disease spreads (new cases/year)
Prevalence
The number of people who develop the disease at a specified time, regardless of when it first appeared. Accounts for old & new cases (number infected/year) and indicates how long the disease occurs in a population
Patterns of incidence terms
- Sporadic Disease
- Endemic Disease
- Epidemic Disease
- Pandemic Disease
Sporadic Disease
Occurs only occasionally
Endemic Disease
Constantly present in a population
Epidemic Disease
Unexpectedly acquired by many people in a given area in a short time (political implications)
Pandemic Disease
Worldwide epidemic
HIV Disease Stats
From 1983-95 HIV was epidemic in US
Now HIV is endemic in US
The incidence in 1995 was >70,000
The Prevalence from 1979-1995 was 500,000
Acute Disease
Symptoms develop rapidly but the disease only lasts a short time (ex. influenza)
Chronic Disease
Symptoms develop slowly (ex. tuberculosis)
Subacute Disease
Intermediate between acute and chronic
Latent Disease
Causative agent is inactive for a time but then activates and produces symptoms (ex. herpes virus)
Herd Immunity
Immunity in most of a population
Factors to host involvement
- Extent of host body affected (local or systemic)
- State of host resistance (resistant, susceptible, or compromised)
- Predisposing conditions (gender, age, lifestyle)
Extent of host body affected
Local Infection
Pathogens are limited to a small area of the body (ex. respiratory infection)
Extent of host body affected
Systemic (generalized) Infection
An infection throughout the body (ex. measles)
Extent of host body affected
Focal Infection
Systemic infection that began as a local infection
Extent of host body affected
Sepsis
Toxic inflammatory condition from the spread of microbes, especially bacteria or their toxins, from a focus of infection
Extent of host body affected: systemic
Septicemia
“blood poisoning”
growth of pathogens in the blood
Septicemia
Bacteremia
Bacteria in the blood
Septicemia
Viremia
Virus in the blood
State of host resistance
Subclinical Disease
No noticeable signs or symptoms. Healthy, resistant host.
State of host resistance
Primary Infection
Acute infection that causes initial illness. Healthy, but susceptible host.
State of host resistance
Secondary Infection
Opportunistic infection after a primary infection. Compromised & susceptible host. (ex. HIV patients contract pneumonia)
Predisposing Factors
Factors that make the body more susceptible to disease.
- Gender (ex. UTIs are more common in women)
- Inherited Traits (ex. Sickle Cell allele)
- Climate/Weather (ex. flu in the winter)
- Fatigue
- Age
- Lifestyle (ex. drinking, smoking, workout, drugs)
- Poor nutrition
- Chemotherapy
People to know
John Snow (1848-1849)
Mapped the occurrence of cholera in London
People to know
Joseph Lister (1850’s)
Used phenol as a disinfectant during surgery to lower post-operative wound infections
People to know
Florence Nightingale (1858)
Showed that improved sanitation decreased the incidence of epidemic typhus
2 Types of disease transmission
Noncommunicable/Common source spread
Results from single common contaminated source (ex. food poisoning)
2 Types of Disease Transmission
Communicable/Propagated Spread
Results from the introduction of a single infected individual into a susceptible population which is propagated to others
3 Types of common source epidemics (noncommunicable)
Point Source Spread
Occurs for a short period of time (ex. bad batch of food)
3 Types of common source epidemics (noncommunicable)
Continuous Common Source Spread
Infection occurs for an extended period of time (ex. bad water)
3 Types of common source epidemics (noncommunicable)
Intermittent Common Source Spread
Infection occurs of a period, stops, then begins again (ex. water is contaminated during floods)
Sources of Infection
Human Reservoirs
- Some pathogens exist only in humans
- Carriers may have inapparent infections or latent diseases (ex. whooping cough)
Sources of Infection
Animal Reservoirs
- Many pathogens move between species & genera
- Zoonoses are diseases transmitted from animals to humans (ex. influenza virus)
Sources of Infection
Nonliving Reservoirs
- Some pathogens are acquired from our environment
ex. cholera is from contaminated water
Types of disease transmission
Contact Transmission
Disease is transmitted upon contact with a surface or substance that contains the disease. Types: Direct, Indirect, Droplet
Types of disease transmission
Vehicle Transmission
Disease that is transmitted through something that people often come in contact with. Types: Waterborne, Foodborne, Airborne, Bloodborne.
Types of Disease Transmission
Vector Transmission
Disease that is transmitted via another living creature. Types: Mechanical and Biological
Types of contact transmission
Direct Contact Transmission
Requires close association between the infected and susceptible host (ex. person-to-person transmission)
Types of contract transmission
Indirect Contact Transmission
Spreads to a host by a nonliving object called a fomite (contaminated surfaces/objects, used needles, door knobs)
Types of contact transmission
Droplet Transmission
Transmission airborne droplets <1 meter (ex. mucous) Not considered airborne over short distances.
Types of vehicle transmission
Waterborne
Disease transmitted via water. (ex. sewage contaminated water)
Types of vehicle transmission
Foodborne
Disease transmitted via food (ex. poorly handled foods, contaminated food supply)
Types of vehicle transmission
Airborne
Disease transmitted via air. Persistent droplet nuclei or dust over a large area. (ex. pollution)
Types of vehicle transmission
Bloodborne
Disease transmitted by transfusion or direct exposure to blood
Vector Transmission
Disease spread via another species (ex. arthropods, fleas, ticks, mosquitoes)
Types of vector transmission
Mechanical Transmission
Arthropod carries pathogen on its feet (ex. a fly walks on dog poop then walks on your food)
Types of vector transmission
Biological Transmission
Pathogen reproduces in the vector and is transmitted via bites or feces (ex. malaria, heartworms)
3 Types of Control Measures
- Eliminate/reduce source/reservoir of infection
- Break the connection between source of infection and susceptible individuals
- Reduce number of susceptible individuals
Healthcare-Associated Infections (HIAs)
aka. nosocomial infections
Acquired while receiving treatment in a health care facility. Affect 1 in 25 hospital patients (incidence rate is increasing)
HAIs result from
Microbes in the hospital
Compromised hosts
Chains of transmission
HAIs result from
Microbes in the Hospital
Normal flora and Horizontal Transfer of R plasmids
HAIs result from
Compromised Host
Broken skin/mucous membrane
Resistance to infection is impaired by disease, therapy, or burns
Altered breathing
HAIs result from
Chains of transmission
Direct from staff & other patients
Indirect from fomites
Airborne from ventilation systems
Controlling HAI
Reduce the number of pathogens
Handwashing, disinfecting tubs used to bathe patients, cleaning instruments scrupulously, using disposable bandages and intubation
Controlling HAI
Infection Control Committees
Dedicated epidemiologists, coordinate staff, regular inspections, spot checks
Types of Epidemiological Investigations
Observational Stuides
Involves data from affected population
Observational Stuides
Descriptive Epidemiology
Collection and analysis of data
Observational Studies
Analytical Epidemiology
Collection and analysis of data from a select group
Observational Studies: Analytical
Retrospective Studies
Uses data from previous cases
Observational Studies: Analytical
Prospective Studies
Use date from current cases to monitor disease progress
Observational Studies: Analytical
Case-control Studies
Use data from previous cases compared to healthy
Observational Studies: Analytical
Cross-sectional Studies
Use data from random, current individuals to monitor disease progress
Types of Epidemiological Investigations
Experimental Studies
Involves a hypothesis & controlled experiments. Very hard to do with people.
Notifiable Infectious Diseases
Diseases in which physicians are required to report occurrence
Notifiable Infectious Diseases
Morbidity Rate
Number of infections from a disease in relation to the population in a given time period
Notifiable Infectious Diseases
Mortality Rate
Number of deaths from a disease in relation to the population in a given time
Morbidity and Mortality Weekly Report (MMWR)
Publication from the CDC
Organizations
CDC
Collects & analyzes epidemiological information in the US
Global
Centers of Disease Control and Prevention in Atlanta, GA
Functions as national focus for:
- Developing and applying disease prevention and control
- Environmental Health
- Health promotion and health education activites
Global
World Health Organization
Worldwide public health organization in Geneva, Switzerland
Emerging Infectious Diseases
Disease that are new, increasing in incidence, or showing a potential to increase in the near future. Most are zoonotic, of viral origin, and likely to be vector-borne
Contributing Factors
- Genetic Recombination (Escherichia coli O157 & avian influenza H5N1)
- Evolution of New Strains (Vibrio cholerae O139)
- Widespread use of Antibiotics and Pesticides (antibiotic-resistant strains)
- Changes in weather patterns (hantavirus in dry, hot conditions)
- Modern Transportation
- Ecological disaster, war, and expanding human settlement
- Animal Control Measures (Lyme disease in deer populations)
- Public Health Failure (Diphtheria, cholera)
