Microbiology:
Week Six

Chapter 11: Epidemiology & Public Health

What is Epidemiology?

Epidemiology can be loosely defined as the study of disease.
Epidemiologists study the factors that determine the frequency, distribution, and determinants of diseases in human populations.
Epidemiologists also develop ways to prevent, control, or eradicate diseases in populations.

Epidemiologic Terminology

A communicable disease is an infectious disease that can be transmitted from one person to another
A contagious disease is a communicable disease that is easily transmitted from person-to-person.
Zoonotic diseases are diseases that humans acquire from animal sources.
The incidence of a particular disease is the number of new cases of that disease in a defined population during a specific time period.
The morbidity rate is the number of new cases of a particular disease that occurred during a specified time period per a specifically defined population (usually per 1,000, 10,000 or 100,000 population).
Prevalence

- Period prevalence is the number of cases of a disease existing in a given population during a specific time period (e.g., during the year 2009).

- Point Prevalence is the number of cases of a disease existing in a given population at a particular moment in time (e.g., right now).

Mortality rate is the ratio of the number of people who died of a particular disease during a specified time period per a specified population
A sporadic disease is one that occurs only occasionally within the population of a particular geographic area; example, tetanus.
An endemic disease is one that is always present within the population of a particular geographic area; example, gonorrhea.
An epidemic disease is defined as a greater than usual number of cases of a disease in a particular region, usually within a short period of time; example, the Legionnaire’s disease epidemic of 1976.
A pandemic is a disease that is occurring in epidemic proportions in many countries simultaneously. Examples include:

- Influenza - the Spanish flu pandemic of 1918 during which more than 20 million people were killed worldwide (500,000 in the U.S.); (2) the H1N1 (“swine flu”) pandemic of 2009-2010.

- HIV/AIDS

- Tuberculosis

-Malaria

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Vocabulary words

Interactions Among Pathogens, Hosts, and the Environment

Whether an infectious disease occurs depends on:

Factors pertaining to the pathogen (e.g., virulence of pathogen, mode of entry, number of organisms)
Factors pertaining to the host (e.g., health status, nutritional status, hygiene, age, travel, lifestyle, etc.)
Factors pertaining to the environment (e.g., physical factors such as climate, season, geographic location; availability of appropriate reservoirs; sanitary and housing conditions; and availability of potable water

The Chain of Infection

There are 6 components in the infectious disease process:

a pathogen
a source of the pathogen (a reservoir)
a portal of exit
a mode of transmission
a portal of entry
a susceptible host

Reservoirs of Infection

The sources of microorganisms that cause infectious diseases are many and varied; they are known as reservoirs of infection or simply reservoirs.

Living reservoirs – humans, pets, farm animals, insects, arachnids

Human carriers:

- Passive carriers

- Incubatory carriers

- Convalescent carriers

- Active carriers

Animals

–Infectious diseases that humans acquire from animal sources are called zoonotic diseases or zoonoses.

–Zoonoses may be acquired by direct contact with an animal, inhalation or ingestion of the pathogen, or injection of the pathogen by an arthropod.

•Examples:

•Rabies

•Lyme disease

•Many others

Arthropods

–Many different types of arthropods serve as reservoirs of infection, including insects (e.g., fleas, mosquitoes, lice) and arachnids (e.g., mites and ticks)

–When arthropods are involved in the transmission of infectious diseases they are referred to as vectors.

•Examples of arthropod-borne diseases:

•Lyme disease

•Malaria

Nonliving Reservoirs - Air, soil, dust, contaminated water and foods, and fomites

Fomites - inanimate objects capable of transmitting pathogens (e.g., bedding, towels, eating and drinking utensils, hospital equipment, telephones, computer keyboards, etc.)

The Most Common Modes of Transmission of Infectious Diseases

Direct skin-to-skin contact
Direct mucous membrane-to-mucous membrane contact by kissing or sexual intercourse
Indirect contact via airborne droplets of respiratory secretions, usually produced by sneezing or coughing
Indirect contact via food and water contaminated by fecal matter
Indirect contact via arthropod vectors
Indirect contact via fomites
Indirect contact via transfusion of contaminated blood or blood products or by parenteral injection using nonsterile syringes or needles

Chapter 12: Healthcare Epidemiology

Introduction

Infectious diseases can be divided into 2 categories:

Those acquired within healthcare facilities (healthcare-associated infections)
Those acquired outside of healthcare facilities (community-acquired infections)

Frequency of healthcare-associated infections (HAIs)

Of approximately 40 million hospitalizations per year in the U.S., an estimated 2 million patients (~5% of the total) acquire HAIs

Healthcare epidemiology: the study of the occurrence, determinants, and distribution of health and disease within healthcare settings facilities
The primary focus of healthcare epidemiology is on infection control and the prevention of healthcare-associated infections
Healthcare epidemiology includes any activities designed to study and improve patient care outcomes

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Public Health Agencies

World Health Organization (WHO)

A specialized agency of the United Nations founded in 1948; www.who.org
Missions: to promote technical cooperation for health among nations; to carry out programs to control and eradicate diseases; to improve the quality of human life

•Investigates outbreaks of Ebola virus, etc.

•Eradicated smallpox

•Attempting to eradicate polio and dracunculiasis

Centers for Disease Control and Prevention (CDC)

A federal agency administered by the U.S. Department of Health and Human Services; located in Atlanta, GA; established in 1946; www.cdc.gov
Mission: “to collaborate to create the expertise, information, and tools that people and communities need to protect their health …”
Certain infectious diseases, known as nationally notifiable diseases must be reported to the CDC.
Publishes Morbidity and Mortality Weekly Report (MMWR).

Measures for prevention and control of epidemics:

Increase host resistance through the development and administration of vaccines that induce active immunity and maintain it in susceptible persons
Ensure that persons exposed to a pathogen are protected against the disease
Segregate, isolate and treat those who have contracted a contagious infection to prevent the spread of the pathogen to others
Identify and control potential reservoirs and vectors of infectious diseases

Healthcare-Associated Infections

Most Common Types of HAIs

The 4 most common types of HAIs, in descending order of frequency, are:

Urinary tract infections (UTIs)
Surgical site infections (also referred to as postsurgical wound infections)
Lower respiratory infections (primarily pneumonia)
Bloodstream infections (septicemia)

Other types: gastrointestinal diseases caused by Clostridium difficile (referred to as Clostridium difficile-associated diseases)

Patients Most Likely to Develop HAIs

Elderly patients
Women in labor and delivery
Premature infants and newborns
Surgical and burn patients
Diabetic and cancer patients
Patients receiving treatment with steroids, anticancer drugs, antilymphocyte serum, and radiation
Immunosuppressed patients
Patients who are paralyzed or are undergoing renal dialysis or catheterization

Major Factors Contributing to HAIs

The 3 major factors that combine to cause HAIs are:

An ever-increasing number of drug-resistant pathogens
The failure of healthcare personnel to follow infection control guidelines
An increased number of immunocompromised patients

Additional Factors Contributing to HAIs

Overcrowding of hospitals and shortages of healthcare staff
The indiscriminate use of antimicrobial agents
A false sense of security about antimicrobial agents
Lengthy and more complicated types of surgery
Increased use of less-highly trained healthcare workers
Increased use of anti-inflammatory and immunosuppressant agents
Overuse and improper use of indwelling devices

What Can be Done to Reduce the Number of HAIs?

Strict compliance with infection control guidelines
Handwashing is the single most important measure to reduce the risks of transmitting pathogens from one patient to another or from one anatomic site to another on the same patient!
Other means of reducing the incidence of HAIs include disinfection and sterilization techniques, air filtration, use of ultraviolet lights, isolation of especially infectious patients, and wearing gloves, masks, and gowns whenever appropriate.

Infection Control

Infection control – the numerous measures taken to prevent infections from occurring in healthcare settings.

Asepsis means “without infection”; there are 2 types:

– Medical asepsis

•Precautionary measures necessary to prevent direct transfer of pathogens from person to person and indirect transfer of pathogens through the air or on instruments, bedding, equipment, and other inanimate objects (fomites)

– Surgical asepsis or sterile technique

•Practices used to render and keep objects and areas sterile

Surgical aseptic techniques are practiced in operating rooms, labor and delivery areas, and during invasive procedures (e.g., drawing blood, injecting medications, urinary and cardiac catheterization, lumbar punctures)

Differences between medical and surgical asepsis:

1.Medical asepsis is a clean technique whereas surgical asepsis is a sterile technique

2.The goal of medical asepsis is to exclude pathogens, whereas the goal of surgical asepsis is to exclude all microorganisms.

Standard Precautions – are to be applied to the care of ALL patients in ALL healthcare settings, regardless of the suspected or confirmed presence of an infectious agent

They provide infection control guidelines regarding hand hygiene; wearing of gloves, masks, eye protection, and gowns; respiratory hygiene/cough etiquette; safe injection practices; lumbar puncture; cleaning of patient-care equipment; environmental control; handling of soiled linens; resuscitation devices; patient placement; and disposal of used needles and other sharps.

Proper Procedure for Glove Removal

Transmission-Based Precautions

Transmission-Based Precautions are used for patients who are known or suspected to be infected or colonized with highly transmissible or epidemiologically important pathogens for which additional safety precautions beyond Standard Precautions are required to interrupt trsansmission within healthcare settings
The three types of Transmission-Based Precautions are:

- Contact Precautions

- Droplet Precautions

- Airborne Precautions

Examples of Diseases Requiring Contact Precautions

Acute viral (hemorrhagic) conjunctivitis; acute respiratory infectious diseases or aseptic meningitis in infants and young children; chickenpox; cutaneous diphtheria; disseminated shingles; extrapulmonary tuberculosis with draining lesion; gastroenteritis in diapered or incontinent persons; impetigo; infection or colonization with multidrug-resistant organisms; major draining abscesses or wound infections; monkeypox; poliomyelitis; severe mucocutaneous herpes simplex infections; smallpox; staphylococcal scalded skin syndrome; major staphylococcal or streptococcal disease of skin, wounds, or burns; viral hemorrhagic fevers due to Lassa, Ebola, Marburg, or Crimean-Congo fever viruses.

Droplet Precautions

Examples of Diseases Requiring Droplet Precautions

Adenovirus infection in infants and young children; adenovirus pneumonia; epiglottitis or meningitis caused by Haemophilus influenzae type b; major skin, wound, or burn infections due to group A streptococcus; scarlet fever in infants and young children; influenza; meningitis or pneumonia caused by Neisseria meningitidis; mumps; Mycoplasma pneumonia; parvovirus B19 skin infection; whooping cough; pharyngeal diphtheria; pneumonic plague; German measles; severe acute respiratory syndrome (SARS); strep throat in infants and young children; rhinovirus infection; viral hemorrhagic fevers due to Lassa, Ebola, Marburg, or Crimean-Congo fever viruses

Airborne Precautions

Gloves
Gown
Duck respirator/ N95

Examples of Diseases Requiring Airborne Precautions

Chickenpox; confirmed or suspected pulmonary or laryngeal tuberculosis; extrapulmonary tuberculosis with draining lesions; disseminated shingles in any patient; localized shingles in immunocompromised patients; measles; monkeypox; severe acute respiratory syndrome (SARS); smallpox
Note that some of these diseases also require Droplet Precautions and/or Contact Precautions

Airborne Infection Isolation Room

The preferred placement for patients who are infected with pathogens that are spread via airborne droplet nuclei (5 mm or less in diameter), and therefore require Airborne Precautions, is an airborne infection isolation room (AIIR)
An AIIR is under negative pressure to prevent room air from entering the corridor
The air evacuated from an AIIR passes through a HEPA filter

Protective Environments

Patients who are especially vulnerable to infection are placed in a Protective Environment - patients with severe burns or leukemia, transplant or immuno-suppressed patients, patients receiving radiation treatment, leukopenic patients, premature infants
The room is under positive pressure and air entering the room passes through HEPA filters

Handling Food and Eating Utensils

Some of the regulations for safe handling of food and eating utensils include:

Using high-quality, fresh food
Properly refrigerating and storing food
Properly washing, preparing, and cooking food
Properly disposing of uneaten food
Covering hair and wearing clean clothes and aprons
Thoroughly washing hands and nails before handling foods
Keeping all cutting boards and other surfaces scrupulously clean
Washing cooking and eating utensils in a dishwasher with a water temperature > 80oC

Handling Fomites

Fomites are nonliving, inanimate objects, other than food, that may harbor and transmit microbes. Examples: patients’ gowns, bedding, towels, hospital equipment, telephone, computer keyboard, etc.
Transmission of pathogens by fomites can be prevented by observing certain rules:

–Use disposable equipment and supplies whenever possible

–Disinfect or sterilize equipment soon after use

–Use individual equipment for each patient

–Use disposable thermometers or thermometer covers

Medical Waste Disposal

General Regulations

Follow OSHA standards for disposal of medical wastes

Disposal of Sharps

Sharps should be handled and disposed of properly
Dispose of sharps in specifically designed puncture-resistant containers (“sharps containers”)

Infection Control Committees and Infection Control Professionals

All healthcare facilities should have some type of formal infection control program in place.

The Infection Control Committee (ICC) is composed of representatives from most of the hospital’s departments, including medical and surgical services, pathology, nursing, hospital administration, risk management, pharmacy, housekeeping, food services, and central supply.

The chairperson is usually an infection control professional such as an epidemiologist or infectious disease specialist, an infection control nurse, or a microbiologist.

Role of the Clinical Microbiology Laboratory (CML) in Hospital Epidemiology and Infection

CML personnel participate in infection control by:

Monitoring the types and numbers of pathogens isolated from hospitalized patients
Notifying the appropriate infection control person should an unusual pathogen or an unusually high number of isolates of a common pathogen be detected
Processing environmental samples, including samples from hospital employees, that have been collected from within the affected ward(s)

Concluding Remarks

HAIs can add several weeks to a patient’s hospital stay and may lead to serious complications and even death.
Insurance companies rarely reimburse healthcare facilities for costs associated with HAIs.
HAIs can be avoided through proper education and disciplined compliance with infection control practices!
All healthcare workers must fully comprehend the problem of HAIs, must be completely knowledgeable about infection control practices, and must personally do everything in their power to prevent HAIs from occurring!

Microbiology: Week Six