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