Epidemiology and Public Health
Nester Chapter 20
Notebook, Page 281
Introduction to Epidemiology Definition
– Epidemiology is the study of the frequency and distribution of disease
Importance of epidemiology– Allows development of guidelines for the
prevention and control of certain diseases Disciplines that make-up epidemiology
– Ecology, Microbiology, Sociology, Statistics & Psychology …….
Epidemiology Definitions and Descriptive Terms
– Attack rate• Proportional number of cases developing in the
population that was exposed to an infectious agent
– Communicable disease• An infectious disease that can be transmitted
from person to person
– Endemic• Disease or other occurrence that is constantly
present in a population
Epidemiology– Epidemic
• Disease or other occurrence with a higher incidence than expected
– Herd immunity• Occurs when a critical conc. of immune hosts
prevents spread of an infectious agent
– Incidence• # of new cases of a disease in a population at
risk during a specific time period
Epidemiology– Index case
• First identified case in an outbreak or epidemic
– Morbidity• Illness; Expressed as rate of illness in a given
population at risk
– Mortality• Death; Expressed as a rate of death in a given
population at risk
– Non-communicable disease• A disease not transmitted from one host to
another
Epidemiology– Outbreak
• A cluster of cases occurring during a brief period; affecting a specific population; may herald an epidemic
– Pandemic• Worldwide epidemic
– Prevalence• Total number of cases in a given population at
risk at some point in time
Spread of Disease– Reservoir
• Natural habitat of disease-causing organism
– Mode of transmission– Portal of entry
• Surface or orifice through which disease-producing agent enters the body
– Portal of exit• Surface or orifice through which disease-
producing agent exits and disseminates
Spread of Disease Types of reservoirs
– Humans• Communicable diseases e.g. smallpox
– Animal reservoirs- zoonotic diseases• Rodents-plague• Giardia• Salmonella
– Environmental reservoirs• Soil• Water
Spread of Disease
Portal of exit– Intestinal organisms– Respiratory organisms– Skin organisms– Genital tract organisms
Spread of Disease Mode of Transmission
– Person to person transmission• Direct contact
– Horizontal spread– Vertical spread
• Droplet transmission– Droplet nucleii in the inhaled air
• Indirect contact– Fomite transmission
Spread of Disease
Mode of transmission (continued)– Contaminated food or water– Infected cut from an organism in the soil– Arthropod vectors
• Ticks• Fleas• Mosquitos
Spread of Disease
Portal of Entry– Respiratory tract– Digestive tract– Urinary tract– Genital tract– Through skin
Factors that influence the Epidemiology of Disease
The infectious dose The incubation period Population characteristics
– Immunity to the pathogen– General health– Age– Gender– Religious and cultural practices– Genetic background
Types of Epidemiological Studies Three major types of studies
– Descriptive studies– Analytical studies– Experimental studies
Types of Epidemiological Studies Descriptive studies occur immediately a
disease outbreak is recognized– Person– Place– Time
• Common source outbreak• Propagated outbreak
Types of Epidemiological Studies Analytical studies are designed to
determine which of the potential risk factors identified in the descriptive studies are actually relevant in the spread of disease– Retrospective studies– Cross-sectional studies– Prospective studies
• Cohort groups
Types of Epidemiological Studies Analytical studies are designed to
determine which of the potential risk factors identified in the descriptive studies are actually relevant in the spread of disease– Retrospective studies
Types of Epidemiological Studies Analytical studies are designed to
determine which of the potential risk factors identified in the descriptive studies are actually relevant in the spread of disease– Cross-sectional studies
Types of Epidemiological Studies Analytical studies are designed to
determine which of the potential risk factors identified in the descriptive studies are actually relevant in the spread of disease– Prospective studies
• Cohort groups
Types of Epidemiological Studies Experimental studies
– To judge• Cause and effect relationship of the risk factors• Cause and effect relationship of preventative
factors and the development of disease
– To assess• value of a particular intervention or treatment
– should be compared against a placebo or a treatment of known effectiveness
– should be a double-blind study
Identifying the Source of an Epidemic
Precise identification of an infectious agent is important– Different disease agents may produce the
same symptoms– A single agent may produce a number of
manifestations– May need identification not only of the
organism but also the precise strain of the organism
Identifying the Source of an Epidemic Precise identification may involve
– Bacteriophage typing– Antibiogram– Surface antigen identification– Genetic analysis
Identifying the Source of an Epidemic Precise identification may involve
– Bacteriophage typing
Identifying the Source of an Epidemic Precise identification may involve
– Antibiogram
Identifying the Source of an Epidemic Precise identification may involve
– Surface antigen identification
Identifying the Source of an Epidemic Precise identification may involve
– Genetic analysis
Infectious Disease Surveillance
National Disease Surveillance Worldwide Disease Surveillance
– Weekly Epidemiological Record
Infectious Disease Surveillance Worldwide Disease Surveillance
– World Health Organization• Provide worldwide guidance in the field of
health• To set global standards for health• To co-operatively strengthen national public
health programs• To develop and transfer appropriate health
technology• Weekly Epidemiological Report
– http://www.who.int/wer/en/
Infectious Disease Surveillance National Disease Surveillance
– National Centers for Disease Control and Prevention (CDC)
• Morbidity and mortality weekly report– http://www.cdc.gov/mmwr/
• 58 notifiable diseases
– State Public Health Laboratory– Local Public Health Agencies– Other components
• hospital labs, physicians, public schools etc.
Infectious Disease Surveillance National Disease Surveillance
– National Centers for Disease Control and Prevention (CDC)
• Morbidity and mortality weekly report• 58 notifiable diseases
Infectious Disease Surveillance National Disease Surveillance
State Public Health Laboratory
Infectious Disease Surveillance National Disease Surveillance
– Local Public Health Agencies
Infectious Disease Surveillance National Disease Surveillance
– Other components• hospital labs, physicians, public schools etc.
Trends in Disease
Reduction and eradication of disease– Small pox– Polio
Emerging Diseases– Newly recognized diseases
• Ebola virus• Hantavirus• HIV
– Familiar diseases that are re-emerging
Trends in Disease
Reduction and eradication of disease– Small pox– Polio
Polio
A disease that has been reduced in incidence
Trends in Disease
Emerging Diseases– Newly recognized diseases
• Ebola virus• Hantavirus• HIV
– Familiar diseases that are re-emerging• Tuberculosis• Syphilis
Trends in Disease Emerging Diseases
– Microbial evolution– Complacency and breakdown of public
health infrastructure– Changes in human behavior– Advances in technology– Population expansion– Development
Trends in Disease
Emerging diseases (continued)– Mass distribution and importation of food– War and civil unrest– Climate changes
Infectious Disease Control in Special Situations Day-care Centers
– Infants in diapers– Young clients are oblivious to hygiene rules– Young children have not acquired immunity
to many common illnesses– Day care staff need to be aware of sanitation
procedures to prevent transmission of disease
Infectious Disease Control in Special Situations Hospitals and Nosocomial infections
– 2% to 10% of all hospitalized patients acquire nosocomial infections
– At least 1/2 of all hospital infections– Many sources of infection
• Therapeutic procedures• Hospital environment• Hospital personnel• Patients own normal flora
Infectious Disease Control in Special Situations Hospitals and Nosocomial infections
– Types of bacteria• Enterococcus• E-coli• Pseudomonas- found in humidifiers of
ventilators, sinks and toilets• Staphylococcus aureus• Other Staphylococci• Streptococcus pyogenes
Infectious Disease Control in Special Situations Hospitals and Nosocomial infections
– Prevention of infections• Use of Universal precautions or body
substance isolation procedures• Compliance with these precautions
– Infection control practitioner– Hospital epidemiologist– Infection control committee