Chapter 19 - Principles of Epidemiology

What are ways of disease transmission?

(1) Contact -direct contact -indirect contact -droplet transmission (2) Food and Water (3) Air (4) Vectors - any living organism that can carry a disease-causing microbe, but most commonly these are arthropods such as mosquitoes, flies, lice, and ticks!

What are healthcare-associated infections (HAIs)? -how many in every 10 deaths is caused by HAIs? -what is a hospital-aquired infection called? -how many admitted patients usually acquire these type of diseases? -why does this occur? -how many of the patients who contract recieve infections from own micrbiota?

-Acquired while receiving treatment in healthcare facility -1 -nosocimial infections (problematic throughout history) -5-10% of patients admitted in U.S. acquire -hospitals are densely populated with unusually susceptible people, and are home to both resistant and virulent pathogens -About 2/3 are from patients' own normal microbiota

How can food and water become contaminated?

-Animal products (meat, eggs) from animal's intestines easily infected -Cross-contamination: transfer from one food to another -Municipal water systems can distribute pathogens to large numbers of people

What is a human reservoir? -is it easy or difficult to control the disease if humans are only reservoir? -what example of human-only reservoir disease did we discuss? -do humans have to show symptoms to be infectious? What is this usually called? what is an example?

-Infected humans are a significant reservoir of infection for many communicable diseases -Often easier to control if humans are the only reservoir; E.g., smallpox (very easy to control!). Sometimes the pathogen is found not only in humans, but also in animals or the environment -Humans carry symptomatic or asymptomatic infections - Symptomatic infections: obvious source of pathogens - Asymptomatic infections: harder to identify, people may not realize they have the disease and can spread it to others. These individuals are carriers for the disease. » Example: Up to 50% of women infected with Neisseria gonorrhoeae are asymptomatic, and easily transmit the disease to others

What are vectors? -what is the most common vector? -what is the difference between mechanical vs. biological contamination?

-Vectors: living organisms that can carry pathogen • Most commonly arthropods: mosquitoes, flies, fleas, lice, ticks; these can carry microbes internally or externally • Transmission can be mechanical or biological - Mechanical: pathogens transmitted on feet of vector - Biological: pathogen transmitted by insect bite, in insect saliva

What is virulence? -what are virulence factors? -what are a 6 examples of how pathogen is able to avoid immune defenses and damage host cell?

-Virulence: ability to cause disease -Virulence factors: factors that allow pathogens to adhere to or penetrate host cell, avoid immune defenses and damage the host cell. Organisms with variety in virulence factors are more likely to cause disease. Examples: • binds mucosal epithelial cells by pili • adhere to intestinal epithelial cells and cause them to take up the pathogen • protected by a capsule • survives within activated macrophages • produces cytotoxin that destroys blood vessels • produces phospholipase that destroy host cell membranes

What is droplet transmission? -is this DIRECT or indirect?

-although physical contact is not needed, respiratory droplets generally fall to ground within a meter from release. DIRECT. -Spread is minimized by covering mouth when sneezing -Particularly important in densely populated buildings (schools, military barracks)

What are two forms of direct contact? -can any contact cause infection? -what is the most important measure to prevent the spread of infectious disease? -some pathogens cannot survive outside of body, how are they frequently passed through direct contact?

-handshake, sexual intercourse -Infectious dose important (e.g., for Shigella is only 10-100 cells, and can happen from handshake) -From hands, pathogens can be ingested: fecal-oral transmission -Handwashing considered single most important measure for preventing spread of infectious disease -Some pathogens cannot survive in environment, require intimate sexual contact (e.g., Treponema pallidum, Neisseria gonorrhoeae)

What is indirect contact? -what are examples of fomites?

-pathogen transmission is by inanimate objects, or fomites. -clothing, table-tops, doorknobs, drinking glasses, toothbrushes, towels

What is a reservoir of infection? -what are examples of reservoirs? -why is it important to identify reservoirs? -is it relatively easy or difficult to control reservoirs?

-the natural habitat in which pathogen lives. -Can be in or on animals or humans, or in the environment (soil, air, water) -Affects extent and spread of a disease -Identification of the reservoir of infection is important in disease control. Usually difficult to control reservoirs. - E.g., control of rats, mice, prairie dogs (reservoirs of Yersinia pestis) prevents plague epidemics in U.S.

If reservoir is an animal, how does pathogen go in and out of host? -what are the four examples that we discussed in class?

Through portals of entry and exit. (1) Intestinal tract pathogens: shed in feces (e.g., Vibrio cholerae) (2) Respiratory tract pathogens: exit in droplets of saliva, mucus (e.g., Mycobacterium tuberculosis, respiratory viruses) (3) Skin pathogens: shed on skin cells (e.g., Staphylococcus aureus) (4) Genital pathogens: semen, vaginal secretions (e.g., Neisseria gonorrhoeae)

Below is list of healthcare-associate infections. Put in order from most common to least common. Bacteremia respiratory tract urinary tract other surgical site

Urinary Tract (32%) Surgical Site (22%) Other (17%) Respiratory Tract (15%) Bacteremia (14%)

Environmental reservoirs are often found in soil (like Clostridium boulinum and Clostridium tenani) Are pathogens with environmental reservoirs easy or difficult to eliminate.

Very difficult. Usually impossible to eliminate.

Non-human reservoirs are the source of many pathogens. What is an example of a non-human animal reservoirs?

Zoonoses (zoonotic diseases) are diseases that primarily exist in animals but can be transmitted to humans (e.g., plague, rabies)

VOCAB __________________: is the percentage of the population that dies from a specific disease

case-fatality rate

What are the two categories of disease? Briefly describe each. -how are they categorized? -are they spread from host to host? -where are the microorganisms that cause disease from? -what are some examples of each?

categorized by type of transmission. 1. Communicable (contagious) diseases • Transmitted (spread) from one host to another • E.g., measles, colds, influenza • Transmission is determined by interactions between environment, pathogen and host • Control of any of these factors may break the infection cycle E.g., improved sanitation (prevent infection); antimicrobial medications (kill or inhibit pathogens); vaccination (increase host resistance) 2. Non-communicable diseases • Do not spread from host to host • Microorganisms most often arise from individual's normal microbiota (e.g. Enterobacter aerogenes) or the environment (e.g. Clostridium tetani)

VOCAB ___________________: constantly present in population • E.g., common cold

endemic diseases

VOCAB _________________: is an unusually large number of cases (e.g. 'flu)

epidemic

NAME THE HOST FACTOR __________ _______________: malnutrition, overcrowding, fatigue increase susceptibility • Developing world more susceptible: crowding, poor food, sanitation

general health

NAME THE HOST FACTOR __________________ _______ _________________: previous exposure or immunization • _____________ ________________ protects non-immune individuals in a population; >90% immunity typically sufficient to protect • Sometimes antigenic variation can overcome herd immunity (e.g., avian flu)

immunity to pathogen heard immunity

VOCAB __________________: is number of new cases in a specific period of time. -It is a measure of the RISK of an individual contracting a disease. AKA Real time. Can find out rates on CDC.gov site. Another def to help explain: __________________ is a measure of the number of new cases of a disease (or other health outcome of interest) that develops in a population at risk during a specified time period.

incidence rate

VOCAB ___________________: is overall death rate in population • In developed countries, most often associated with non- communicable diseases (e.g., cancer, heart attack) • Communicable disease are the major cause of death in developing countries

mortality

How does a pathogen transfer to a host?

must leave its reservoir to enter and colonize a susceptible host

VOCAB ___________________: a group of cases at specific time and population

outbreak

VOCAB _________________: is total number of cases at any time or for a specific period in a given population. Reflects overall impact of disease on society; includes old and new cases, as well as duration of disease

prevalence

Are epidemiologists concerned about the number of cases or the rate of infection?

rate of infection. (concerned with percentage of cases rather than individual cases).

VOCAB ___________________: disease occur rarely (e.g. typhoid)

sporadic

How have many diseases been reduced or eradicated? -what two diseases is the U.S. working on eradicating?

• Many diseases reduced through improved sanitation, reservoir and vector control, vaccination, and antibiotic treatment; smallpox has been eradicated globally • In U.S., many formerly common diseases rare. Work underway to eradicate measles, polio

What is epidemiology? -what is an epidemiologist?

Study of disease patterns in populations. (health detectives) collect and compile data about sources of disease and risk factors. They design infection control strategies to prevent or predict spread of disease • Use expertise in diverse disciplines including ecology, microbiology, sociology, statistics, and psychology • Many of our daily habits (handwashing, waste disposal) are based on their work

NAME THE HOST FACTOR __________________: Women more likely to develop urinary tract infections - Urethra is shorter; microbes more likely to go up to bladder

Gender

NAME THE HOST FACTOR __________________ ________________: • Natural immunity varies widely • Specific receptors may differ (e.g., lack of receptor on red blood cell gives immunity malaria organism; lack of receptor on white blood cell reduces susceptibility to HIV)

Genetic Background

NAME THE HOST FACTOR ________________ _________ _____________________ ___________________: • Breastfeeding provides protective antibodies to infant • Consumption of raw fish can increase exposure

Religious and Cultural Practices

What are other examples of reservoirs of infectious agents in healthcare settings? Briefly explain.

1. Other patients: pathogens discharged via skin cells, respiratory droplets, other bodily secretions and excretions 2. Healthcare Environment: some Gram-negative rods can survive in sinks, respirators and toilets - Many nosocomial infections can be traced to contaminated soaps, disinfectants or other aqueous solutions e.g., Pseudomonas aeruginosa 3. Healthcare workers: sick workers may be carriers of pathogens (e.g., Staphylococcus aureus, Streptococcus pyogenes) 4. Patient Micrbiota: invasive procedures can transmit normal microbiota to sterile body sites; compromised immune system may allow infection to develop 5. Fomite Transmission-Medical Devices - Often break the first-line barriers of defense (e.g., catheters, IV, mechanical respirators, inadequately sterilized invasive instruments 6. Direct Transmission-Healthcare Personnel - Must be extremely vigilant with handwashing, disinfecting, and wearing gloves 7. Airborne Transmission - Positive air pressure, careful mopping and HEPA filters can reduce transmission

Some populations more than others are likley to be affected by a given disease-causing agent. What are a few host factors that we discussed that influence epidemiology?

1. immunity to pathogen 2. general health 3. age 4. gender 5. religious and cultural practices 6. genetic background

NAME THE HOST FACTOR ___________: very young, elderly generally more susceptible • Immune system less developed in young; weakens in old • Elderly also less likely to update immunizations

Age

VOCAB. ____________________: is percentage of people who become ill in population after exposure. Reflects infectious dose and immune status of population

Attack Rate

VOCAB ______________________: is the incidence of disease in population at risk • Contagious diseases (e.g., influenza) often have high ____________ rate: infected individual may transmit the disease to several other people

Morbidity

VOCAB ________________: is a global epidemic (e.g. AIDS)

Pandemic