Epidemiology and Public Health Nester Chapter 20 Notebook, Page 281

Introduction to Epidemiology n Definition –Epidemiology is the study of the frequency and distribution of disease n Importance of epidemiology –Allows development of guidelines for the prevention and control of certain diseases n Disciplines that make-up epidemiology –Ecology, Microbiology, Sociology, Statistics & Psychology …….

Epidemiology n 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 n Types of reservoirs –Humans Communicable diseases e.g. smallpox –Animal reservoirs- zoonotic diseases Rodents-plague Giardia Salmonella –Environmental reservoirs Soil Water

Spread of Disease n Portal of exit –Intestinal organisms –Respiratory organisms –Skin organisms –Genital tract organisms

Spread of Disease n 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 n Mode of transmission (continued) –Contaminated food or water –Infected cut from an organism in the soil –Arthropod vectors Ticks Fleas Mosquitos

Spread of Disease n Portal of Entry –Respiratory tract –Digestive tract –Urinary tract –Genital tract –Through skin

Factors that influence the Epidemiology of Disease n The infectious dose n The incubation period n Population characteristics –Immunity to the pathogen –General health –Age –Gender –Religious and cultural practices –Genetic background

Types of Epidemiological Studies n Three major types of studies –Descriptive studies –Analytical studies –Experimental studies

Types of Epidemiological Studies n Descriptive studies occur immediately a disease outbreak is recognized –Person –Place –Time Common source outbreak Propagated outbreak

Types of Epidemiological Studies n 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 n 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 n 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 n 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 n 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 n 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 n Precise identification may involve –Bacteriophage typing –Antibiogram –Surface antigen identification –Genetic analysis

Identifying the Source of an Epidemic n Precise identification may involve –Bacteriophage typing

Identifying the Source of an Epidemic n Precise identification may involve –Antibiogram

Identifying the Source of an Epidemic n Precise identification may involve –Surface antigen identification

Identifying the Source of an Epidemic n Precise identification may involve –Genetic analysis

Infectious Disease Surveillance n National Disease Surveillance n Worldwide Disease Surveillance –Weekly Epidemiological Record

Infectious Disease Surveillance n 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 –

Infectious Disease Surveillance n National Disease Surveillance –National Centers for Disease Control and Prevention (CDC) Morbidity and mortality weekly report – 58 notifiable diseases –State Public Health Laboratory –Local Public Health Agencies –Other components hospital labs, physicians, public schools etc.

Infectious Disease Surveillance n National Disease Surveillance –National Centers for Disease Control and Prevention (CDC) Morbidity and mortality weekly report 58 notifiable diseases

Infectious Disease Surveillance n National Disease Surveillance State Public Health Laboratory

Infectious Disease Surveillance n National Disease Surveillance –Local Public Health Agencies

Infectious Disease Surveillance n National Disease Surveillance –Other components hospital labs, physicians, public schools etc.

Trends in Disease n Reduction and eradication of disease –Small pox –Polio n Emerging Diseases –Newly recognized diseases Ebola virus Hantavirus HIV –Familiar diseases that are re-emerging

Trends in Disease n Reduction and eradication of disease –Small pox –Polio

Polio n A disease that has been reduced in incidence

Trends in Disease n Emerging Diseases –Newly recognized diseases Ebola virus Hantavirus HIV –Familiar diseases that are re-emerging Tuberculosis Syphilis

Trends in Disease n Emerging Diseases –Microbial evolution –Complacency and breakdown of public health infrastructure –Changes in human behavior –Advances in technology –Population expansion –Development

Trends in Disease n Emerging diseases (continued) –Mass distribution and importation of food –War and civil unrest –Climate changes

Infectious Disease Control in Special Situations n 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 n 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 n 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 n 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