IPC - Module 2

Question 1

Microorganisms are said to be “ubiquitous”, which means that…

Answer 1

…that they are found everywhere … in our environment and on our bodies. Note that most organisms are found in warm, moist environments (humans and animals), and the least are found in treated water and on dry surfaces.

Question 2

Normal Flora

Answer 2

Under normal circumstances, humans enter this world “germ free.” The placental barrier between mother and fetus prevents microbial penetration. In the few cases where bacteria or viruses invade the fetus in the uterus, the fetus may not develop normally or may die in-utero.

Following birth, microbial populations rapidly establish themselves on the skin and mucous membranes lining the gastrointestinal, respiratory and genital tracts. The microorganisms establish more or less permanent residence, do not produce disease under normal circumstances and are known as normal flora.

Question 3

Normal Flora in different body sites

Answer 3

The composition of normal flora is fairly constant for a given site. For example, most people basically have the same normal flora in the mouth. However, the normal flora composition varies depending on the site: normal flora of the mouth is very different from normal flora of the intestine or the skin.

Question 4

Normal flora of the large intestine

Answer 4

The large intestine is the area of the body that has the greatest normal flora population. There are millions of bacteria in 1 gram of feces and in fact, bacteria make up the bulk of fecal material. A rod-shaped bacterium called Escherichia coli (E.coli) is found in the feces of most people. The normal intestinal flora plays an important role in food digestion and evacuation of feces. E. coli also produce Vitamin K in the colon. The vitamin K is absorbed and travels to the liver where it is incorporated into clotting factors. A lack of E.coli in the colon can ultimately lead to a bleeding disorder. There are many types of E.coli. and while some are vital to good health, others such as E.coli 0157 H7, also known as “hamburger disease”, can cause severe illness.

Question 5

Normal Flora of the Upper Respiratory Tract

Answer 5

The mucous membranes of the upper respiratory tract establish their own specific normal flora and many of these bacteria are called Streptococcus viridans. These bacteria occupy attachment sites on host cells and prevent pathogenic bacteria from invading respiratory tissue.

Question 6

Normal Flora of the skin

Answer 6

The outer surfaces of the body encounter many bacteria but only a few are able to grow on the cool, dry and salty environment of the skin. Staphylococcus epidermidis (Coagulase negative Staphylococcus) make up the majority of the normal flora of the skin although a few other bacteria flourish along hair follicles and sweat glands.

Question 7

Factors that affect Normal Flora

Answer 7

Two factors that may alter the composition of normal flora are:

Excess moisture on the skin. This contributes to an increase in the staphylococci on skin surfaces. Skin under a wide ring or watch strap will have more normal flora than exposed skin. Health care workers wear latex or vinyl gloves when performing certain procedures and the moisture resulting from this may increase the amount of normal flora on their hands.
Antibiotic use. This will often alter normal flora. As the sensitive bacteria are killed, other more resistant strains are allowed to dominate. Patients are more prone to the antibiotic resistant bacteria that may be found in the hospital environment.

Question 8

Contamination

Answer 8

Contamination describes the situation where microorganisms are introduced to a body site where they are not expected, but there is no growth of the microbes. There is no increase in numbers of microbes and no damage to the host. For example, if saliva from the mouth gets on the skin, the skin is contaminated with normal mouth bacteria. The mouth bacteria on the skin as contaminants are easily removed by normal hand hygiene procedures

Question 9

Colonization

Answer 9

Colonization implies contamination with an organism that is not normal to a site, however, actual growth of the microbe does occur. There is still no damage to the host, at least initially. Colonization can occur on a normally sterile area or a site with normal flora. In some cases, colonization may lead to disease but in other cases it never does cause damage to the host. Many patients in intensive care units requiring ventilated-assisted breathing become colonized in the upper airways by fecal bacteria. These bacteria may be present for a period of time and then disappear uneventfully or, in some cases, may set the stage for pneumonia. Staphylococcus aureus as well as Methicillin Resistant Staphylococcus aureus may colonize in the nares (nose). The person is then said to be a “carrier” and can pass the organisms on to susceptible hosts.

Question 10

Infection & Disease

Answer 10

Infection and Disease are often used interchangeably and mean that the host has been colonized with microorganisms and host damage has resulted.

The true definitions of the terms do differ: Infection implies the host has been invaded with an organism but there are no signs of host injury, while disease implies the host has been infected and host injury is evident.

For example, the terms are often used correctly to describe patients with AIDS. A person may be infected with the HIV virus but show no host injury for some period of time. Once the symptoms of AIDS become evident, the host is described as having the disease.

A second example: If Staphyloccocus aureus, which is not normally found on the skin, established itself in a hair follicle, it would be called an infection. If a swollen, painful, red pus filled eruption occurred, it would be called the disease “carbuncle”.

Question 11

Pathogen

Answer 11

A pathogen is a disease-causing organism. Generally speaking, exposure to a pathogen results in infection and ultimately disease.

Question 12

Etiology

Answer 12

The etiology or cause of the disease is an organism

Question 13

Virulence

Answer 13

Virulence is the degree of pathogenicity. There are many virulence factors, and the more of these factors a micro-organism has, the easier it can cause disease

Question 14

Virulence factors include..

Answer 14

-Enzymes that dissolve hyaluronic acid (tissue cement), collagen and fibrin clots, allowing bacteria to spread faster in the tissue
-Substances that destroy red blood cells, releasing iron necessary for bacterial growth
-Substances that destroy white blood cells, weakening body defenses
-Capsules, or slimy coatings, which prevent phagocytic white blood cells from engulfing and destroying the microorganism. Bacterial pneumonia is caused by the capsulated organism, Streptococcus pneumonia. The young and the elderly are particularly susceptible to this, as their white blood cells may not be as able to phagocytize and destroy the bacteria.

Question 15

Non-pathogen

Answer 15

A non-pathogen is an organism that is not able to cause disease. A few bacteria fit this description but as people with impaired immune systems are being infected with microorganisms previously considered to be non-pathogenic, the list gets shorter.

Question 16

low-grade pathogens or opportunistic pathogens

Answer 16

Some microorganisms are low-grade pathogens or opportunistic pathogens. These organisms are non-pathogenic under most circumstances (often normal flora) but may cause disease when the host’s defenses are lowered, usually by other predisposing conditions or when the microorganisms move to another part of the body.

Question 17

Exotoxins

Answer 17

Produced mainly by gram positive bacteria
Released from intact bacterial cells
Carried away from the infection site by blood
Attack a specific target tissue
For example, the tetanus toxin affects the central nervous system and interferes with transmission of impulses from the brain to groups of muscles. One of the first symptoms of tetanus is often a clenched jaw that cannot be released, hence the name “lock jaw.”

Question 18

Endotoxins

Answer 18

Produced by gram negative bacteria; located in the cell wall.
Released only when the bacterial cells are disrupted.
Have a more generalized effect on the host, rather than attacking a specific tissue.
May be responsible for fever or general malaise and aches accompanying bacterial infections.
Can also have life-threatening effects such as drop in blood pressure and circulatory collapse. The reason for this is not really understood.
The use of antibiotics can sometimes cause serious complications, as the bacterial cell is destroyed, resulting in the sudden release of endotoxins and subsequent shock.
For example, pyrogens are endotoxins that cause fever; the endotoxin associated with “hamburger disease” bacteria can cause potentially life-threatening kidney damage; Neisseria meningitidis can cause shock, circulatory collapse, tissue and kidney damage.

Question 19

Other substances called toxins cause damage to sites far-removed from the initial site of infection. The effect of a toxin on a host differs with the type of toxin. There are two types of toxins:

Answer 19

1. Exotoxins
2. Endotoxins

Question 20

There are three elements required for transmission of infection:

Answer 20

1. A reservoir or source of infectious microbes (source of infection)
2. A means of transmission for the microbes (how spread)
3. A susceptible host (who gets it)

These three elements make up what is called the chain of infection. For an infection to occur, the chain must be complete. If the process is stopped at any point, infection can be prevented.

The susceptible host who becomes infected may then become the reservoir of microorganisms and the chain is repeated.

Question 21

How do you break the chain of infection?

Answer 21

Breaking the chain of infection means stopping infections at the source, eliminating means of transmission, or reducing the susceptibility of potential hosts. Infection prevention and control programs are directed towards preventing transmission.

Question 22

Ways to break the chain of infection..

Answer 22

-Immunization and tuberculin testing (module 3)
-Routine practices and additional precautions
PPE (personal protective equipment)
Hand Hygiene (module 5)
-Sterilization and disinfection (module 6)

Question 23

Reservoirs of Infectious Microorganisms
Three categories of reservoirs exist for infectious microbes:

Answer 23

Human
Animal
Non-living

Question 24

Human Reservoirs

Answer 24

The principle reservoir of human infectious disease is the human body itself. This includes people with disease and “carriers.”
People with disease harbor thousands of microorganisms that are easily passed to other people. Once a person has disease symptoms, care may be taken to prevent transmission of microorganisms. Unfortunately, there are often more infectious organisms present during the early stages of the disease when the person has no idea they are infectious.

Question 25

Carriers

Answer 25

The human reservoir also includes carriers. A carrier is defined as a person harboring pathogenic organisms but who has no signs of infection. The classical example is a typhoid carrier. This is a person who has usually had typhoid and recovered, but some of the typhoid bacteria have remained in the body, often in the gall bladder. These bacteria are excreted sporadically in the feces where they may directly infect another person or contaminate water supplies.

Question 26

Animal Reservoirs

Answer 26

Both wild and domestic animals may serve as the reservoir of infectious organisms for humans. Zoonoses are diseases that are primarily found in animals but may be transmitted to humans.

Animals play an important role in Salmonella infections where the animal is usually poultry and man is infected by ingestion of improperly cooked poultry.

Other examples of zoonoses are the Hanta virus carried by deer mice and rabies carried by dogs, racoons and other wild animals.

Question 27

Zoonoses

Answer 27

Zoonoses are diseases that are primarily found in animals but may be transmitted to humans.

Question 28

convalescent carrier

Answer 28

Even if a person has recovered from a disease, they may still be carrying infectious organisms. This person is called a convalescent carrier.

Question 29

Chronic Carrier

Answer 29

If a carrier is still carrying the organisms after six months, they are called a chronic carrier.

Question 30

Non living reservoirs

Answer 30

Very few microorganisms found in soil and water are capable of causing disease. Two notable exceptions are botulism and tetanus. The spores responsible for both of these diseases are found in soil, however, simple contact with soil will not result in disease.

Botulism is a type of food poisoning and the spores must first grow in food and produce toxin before disease results.

Tetanus only results when spores are introduced into human tissue under conditions where there is little or no oxygen present. This oxygen-free environment is necessary for the spores to germinate in human tissue.

The non-living reservoirs of health care facilities are of concern to health care workers. Bacteria will grow in most moist environments in these institutions and may become important reservoirs of bacteria responsible for hospital acquired infections.

Leaking drain pipes, wet equipment, therapy pools, and sinks have all been identified as sources of infectious bacteria.

Question 31

Transmission of Infectious Microbes

Answer 31

There are 3 principle routes that causative agents of disease can be transmitted from the reservoir to a susceptible host. These are:

Contact, Vehicle, and Vector.

Question 32

Contact Transmission

Answer 32

The spread of microorganisms by direct contact, indirect contact and droplet transmission.

Question 33

Direct Contact Transmission

Answer 33

In direct contact transmission shown in the drawing above, there is direct physical contact between the reservoir and the host. There is no intermediate object involved and for this reason person-to-person transmission means the same thing. Touching, kissing and sexual intercourse are the usual forms of direct contact transmission. Many diseases such as colds, flu, Streptococcal sore throat and Gonorrhea are transmitted this way.

Question 34

Indirect Contact Transmission

Answer 34

Indirect contact transmission, shown in the drawing above, occurs when the infectious agent is transferred from the reservoir to a non-living object, or fomite, and then to the susceptible host. Bedding, towels, eating utensils, diapers, toys, syringes, endoscopes, uncovered knobs and handles in dental offices, thermometers and contaminated tissues (Kleenex) are fomites that may be involved in direct transmission of infectious agents in the health care setting.

An example would be the transmission of colds – a person coughs on their hand, touches something, second person touches same item and spreads the virus to their own mucous membranes. Hepatitis B can be spread via dried blood to a cut on a second susceptible person.

Question 35

Droplet transmission

Answer 35

Droplet transmission as shown in the drawing above is transmission in which the infectious microbes are contained in mucus droplets discharged from the respiratory tract of the reservoir. These relatively large particles only travel one meter or less from the reservoir and the person being infected must be in close proximity. Colds, the flu, Staphylococcal pneumonia, and whooping cough are spread this way.

The definition indicating that droplets fall within one meter is currently under review. The distance may increase to two meters for this definition, as the one meter rule was based on information from an informal study done in 1922.

Question 36

Vehicle Transmission

Answer 36

Vehicle transmission refers to the transmission of infectious microbes by an agent such as food (e.g., unwashed, contaminated foods such as fruit and vegetables), water, air, blood or medication. The “vehicle” keeps the microbe alive until it is ingested or inoculated by another host.

It is common for several people to be infected at the same time, is uncommon in a clinical setting, and usually occurs in the community.

Question 37

Airborne transmission / droplet nuclei

Answer 37

Airborne transmission involves mucus droplets that travel further than one meter from the reservoir. They are tiny particles that contain the microorganism and remaining suspended in the air for a long period time and float great distances on air currents are called droplet nuclei.

Few diseases are actually transmitted by droplet nuclei, but tuberculosis is often spread by this method of transmission. Severe acute respiratory syndrome (SARS) is another example of airborne transmission via droplet nuclei.

Although droplet nuclei are too small to be seen, you can imagine them if you think of seeing dust particles floating in the air in a sunbeam.

Question 38

Vector Transmission

Answer 38

Vectors are insects that carry infectious organisms from one host to another. Malaria spread by mosquitoes, Rocky Mountain spotted fever spread by ticks and West Nile virus spread by mosquitoes are examples.

Question 39

Susceptible Host

Answer 39

Host susceptibility determines whether an encounter with an infectious microbe will result in disease. Host susceptibility is influenced by a number of factors including age, health and immune status of the individual, as well as the dose of the infectious agent to which the individual is exposed.

-Newborns whose immune systems are not fully developed and the elderly whose immune systems are not functioning properly are more susceptible to infection.
A person’s resistance to infection is impaired by factors such as poor nutrition, alcoholism, pre-existing infection and underlying disease.
-Therapeutic measures such as chemotherapy, radiation and antibiotics alter the immune status of the individual.
-Procedures such as surgery, anesthesia and insertion of catheters can also leave a person more susceptible to infection.
-The infectious dose, or number of organisms required to establish an infection, will vary with the microbe. The infectious dose for Salmonella bacteria is about 100,000 organisms; for Shigella (bacteria that cause dysentery), the infectious dose is much lower - somewhere between 10 and 100.

An individual who has received a vaccination against a disease-causing microbe, or someone who has recovered from a particular infection, will have produced antibodies against the pathogen and will be a less susceptible host on subsequent exposures to the micro-organism.

Question 40

Portals of Entry for Infectious Microorganisms

Answer 40

Once an infectious agent reaches the new host, there are specific portals that allow entry. Not all pathogens enter the host via the same route. Microorganisms may gain access to the body through the skin, mucous membranes and the placenta, or by the parenteral route.

Question 41

Skin - portal of entry

Answer 41

Very few organisms are able to gain entry to the body through the intact skin. However, microbes can penetrate:

Hair follicles or sweat glands (e.g., boils and styes)
If the skin is excessively moist (e.g., infected diaper rash). Children are generally more prone to infections due to the delicate nature of their skin.
If the skin is broken as a result of trauma injury, surgical incision or a simple abrasion (e.g., eczema - the disruption in the skin as a result of this condition predisposes to infection, particularly with Staphylococcus aureus)

Question 42

mucous membranes - portal of entry

Answer 42

The mucous membranes servings as portals of entry include those that line the respiratory, gastrointestinal and genital tracts. Each mucous membrane has its own set of microbes capable of entering by that route. For example:

Influenza virus gains entry to the body via respiratory mucosa.
Hepatitis A virus gains entry through the gastrointestinal tract.
Organisms causing sexually transmitted infections (diseases) (STIs formerly called STDs) such as herpes, chlamydia, hepatitis B and AIDS gain entry through the genital mucosa.

Question 43

Placenta - portal of entry

Answer 43

The placental membrane provides a filter for mother’s blood entering fetal circulation and very few microorganisms are able to pass this barrier. There are a few notable exceptions including rubella virus (German measles) and the viruses causing hepatitis B and AIDS.

Question 44

Parenteral Route (think POKE)

Answer 44

The term parenteral means introduction of something into the body by a route that bypasses the gastrointestinal tract. The parenteral portal of entry for infectious organisms includes intravenous or intramuscular injection of contaminated solutions. Punctures, bites, cuts, surgical wounds and trauma injuries all allow entry of microorganisms by the parenteral route.

Question 45

Sign

Answer 45

A sign is a characteristic of a disease that can be observed by examining the patient. Signs of disease include fever, redness and swelling.

Question 46

Symptom

Answer 46

A symptom is a characteristic of the disease that can be observed or felt only by the patient. Symptoms include things such as pain, nausea and malaise.

Question 47

Fever

Answer 47

An increase of 1°C above the normal body temperature is called fever, or pyrexia. (Normal body temperature range is 36.1°C to 37.8°C.)

Certain chemical substances released from micro-organisms cause the body’s “thermostat” to be reset at a higher temperature.

Heat is generated through:

Constriction of the blood vessels (less blood goes to the skin surface where heat would be lost due to evaporation)
An increased metabolic rate
Shivering (mechanical generation of heat)
These activities cause the core body temperature to increase, but the skin remains cold. The person has the “chills” until the new higher body temperature is reached.

When the chemicals that trigger the temperature increase are no longer present, the thermostat setting returns to normal, and the body experiences heat loss. Blood vessels dilate (widen) allowing more blood to circulate close to the skin surface to lose heat. This is accompanied by sweating, another heat loss activity and an indication the fever has broken.

Fever speeds up the metabolic rate in body cells and may facilitate phagocytosis and tissue healing. Fever is one of the few measurable signs of disease that can be used to monitor a patient’s condition.

Question 48

Lymph Node Swelling

Answer 48

The lymphatic system is a series of vessels that drain fluid from tissues and return it to the blood stream. As the fluid moves along the lymphatic vessels, it passes through lymph nodes.

Lymph node swelling may occur during infections as a result of:

Microbes from tissue fluid being trapped in a lymph node, multiplying there and causing infection of the node
Multiplication of lymphocytes responsible for immunity which are located in the lymph nodes
A single swollen node may indicate an infected node but multiple swollen nodes usually indicate the immune system is responding to the micro-organism.

Many of the lymph nodes are in deep tissue and cannot be felt through the skin. There are three locations where the lymph nodes are close to the skin and can easily be palpitated1:

Cervical nodes in the neck
Axillary nodes under the arms
Inguinal nodes in the groin

Question 49

Infammation

Answer 49

When host cells are invaded by micro-organisms, they respond by releasing histamine. Histamine initiates the inflammatory response. Other insults to host tissues such as trauma and chemical agents will also initiate the inflammatory response.

The four cardinal signs and symptoms of inflammation are: heat, redness, pain, and swelling. Tip: To remember the signs and symptoms of inflammation, think “HRPS.” (heat, redness, pain and swelling).

Question 50

Histamine release results in:

Answer 50

Vasodilation (widening of the blood vessels) which increases blood flow to the injury site causing heat and redness.
Increased permeability of the blood vessels, which causes fluid to leak from the vessels into the surrounding tissues creating swelling and pain.

Question 51

How histamine release & inflammation help the host clear the tissue of infecting micro-organisms:

Answer 51

An increased number of phagocytic white blood cells are attracted to the area to engulf and destroy bacteria. They also present antigens (parts of the micro-organisms) to lymphocytes to activate antibody production.
Antibodies that may already be present in the blood are brought to the injury site. These antibodies coat the bacteria in preparation for phagocytosis or neutralize toxins.
Clotting elements from the blood move to the injury site to surround and isolate the microbes.

Question 52

Other signs of infection that result from the inflammatory response include:

Answer 52

Purulent exudates: Otherwise known as pus. This represents phagocytic white blood cells that have been killed in action.
Leukocytosis: This term means an increase in the number of white blood cells and it is the body’s response to the increased need for these cells.

Question 53

Acute Disease

Answer 53

A disease in which symptoms develop rapidly and the disease runs its course quickly. E.g., measles, the common cold.

Question 54

Chronic Disease

Answer 54

A disease in which symptoms develop slowly and the disease is slow to disappear. E.g., tuberculosis.

Question 55

Latent Disease

Answer 55

A disease characterized by periods of inactivity either before symptoms appear or between attacks. E.g., Herpes infection.

Question 56

Localized Infection

Answer 56

An infection confined to one area of the body. A streptococcal sore throat is a localized infection as long as the bacteria do not spread to other areas.

Question 57

Focal Infection

Answer 57

An infection confined to a specific area but pathogens from it, or their toxins, can migrate to other areas. E.g., abscessed tooth.

Question 58

Systemic Infection

Answer 58

An infection in which the pathogen is spread to multiple organs or tissues of the body, often traveling via blood or lymph; also called disseminated infection

Question 59

Septicemia

Answer 59

The presence and multiplication of pathogens in blood.

Question 60

Bacteremia

Answer 60

The presence but not multiplication of bacteria in blood; they are merely in transit. E.g., mouth bacteria in blood after teeth cleaning or tooth extraction.

Question 61

Viremia

Answer 61

The presence but not multiplication of viruses in blood; again they are just in transit. E.g., chicken pox: after the virus enters via the respiratory tract, there is a period of viremia during which the viruses are transported to the skin where they localize and cause the characteristic rash.

Question 62

Toxemia

Answer 62

The presence of toxins in the blood.

Question 63

Exogenous Infection

Answer 63

The micro-organisms causing the infection come from outside the host – from another person, animal or the environment.

Question 64

Endogenous Infection

Answer 64

The micro-organisms causing the infection come from within the host’s body, often normal flora organisms. A urinary infection is a typical example of an endogenous infection where the host’s own fecal bacteria find their way into the urinary system and cause infection.

Question 65

Primary Infection

Answer 65

An infection in a previously healthy individual.

Question 66

Secondary Infection

Answer 66

An infection that immediately follows a primary infection, caused by a different micro-organism.

Question 67

Nosocomial Infection

Answer 67

Are infections acquired during a stay in a hospital (HAI or hospital acquired infections) or other health care facility (HCAI healthcare associated infections).

Question 68

HAI or HCAI Rates

Answer 68

Accurate figures revealing the actual number of patients affected by nosocomial infections are hard to obtain. Most sources give the rate to be somewhere between 5 and 15% of hospitalized patients. The rates vary depending on the nature of the patient population. A pediatric hospital would have a different rate than a geriatric hospital. The Unites States Center for Disease Control and Prevention estimated in 2020 that 5% of hospital admissions resulted in nosocomial infection or approximately 730,000 people, with about 10% of those resulting in death.

According to the Canadian Patient Safety Institute, “In Canada, health care associated infections (HCAI) kill 8,000 – 12,000 people every year.” Therefore the CPSI has launched a hand hygiene program to reduce the number of deaths from Health care associated infections (nosocomial infections).

Question 69

Factors contribute to nosocomial infections - Hospital microorganisms

Answer 69

Hospital microorganisms: There tends to be a concentration of pathogenic bacteria in the hospital environment. Infected patients bring bacteria into the hospital with them. Warm, moist areas of hospitals perpetuate growth of bacteria. Often, only antibiotic resistant strains of bacteria survive in hospital environments, which makes the reservoir of bacteria potentially more dangerous.

Question 70

Factors contribute to nosocomial infections - Immunodeficient (Immunocompromised) patient

Answer 70

Immunodeficient (Immunocompromised) patient: Patients are in hospitals because they are sick and often do not have a fully-functional defense system. Treatments in hospitals can compromise the immune system and superficial defenses making the patient more susceptible to infection. A patient in an intensive care unit with a ventilator breathing for them is a prime candidate for a respiratory infection like ventilator assisted pneumonia (VAP), because the ventilator bypasses the normal defenses of the upper respiratory tract. Many of the drugs used to treat cancer weaken the defenses of the body to the extent that the patient may be infected with opportunistic pathogens.
The term immunodeficient replaces the term immunocompromised. Immunodeficiency occurs when a patient’s immune system is defective, and the B and T cells are unable or only partially able to respond to foreign substances such as bacteria, viruses and fungi. Immunodeficiency may either be congenital (e.g., hypogammaglobulinemia) or acquired (e.g. HIV, renal failure). It may be temporary (chemotherapy for cancer, some drug therapies used for rheumatoid arthritis) or life long (post organ transplant).

Question 71

Factors contributing to nosocomial infection - Transmission

Answer 71

Transmission: A number of factors related to life in a hospital contribute to transmission of pathogenic bacteria. Infected patients can easily disseminate pathogens to other patients because of the close proximity in hospital wards. Hospital staff visit multiple patients during a shift and pathogens are readily transferred by their activities. Many procedures in the hospital provide openings to normally protected areas. Needles, catheters, shunts and incisions all invite pathogenic bacteria into normally sterile areas.

Question 72

Most common nosocomial infections
The most common nosocomial infections in order of occurrence are:

Answer 72

Urinary tract infections: Usually related to bladder catheterization when fecal bacteria colonizing the urethra move up into the bladder. E.coli is frequently the causative agent.

Surgical wound infections: Usually caused by Staphylococcus aureus introduced into the wound site during surgery or changing of dressings. The bacteria may come from hospital staff since many (up to 60%) are staph carriers, harboring these bacteria in their nasal passages with no sign or symptom of infection. (Note: Staphylococcus aureus is a different species than the staphylococci found as normal flora on the skin.) Some strains of Staphylococcus aureus have become resistant to many antibiotics and pose an expensive challenge for treatment.

Pneumonia: Often in patients on a respiratory device. The mortality rate is much higher with this type of nosocomial infection.

Question 73

Antibiotic

Answer 73

An antibiotic is defined as a substance, produced by a microorganism (for example by a fungus), which in small amounts inhibits the growth of, or kills, another microorganism (bacteria). The ideal antibiotic destroys the harmful microorganism without damaging the cells or tissues of the host.

Question 74

First antibiotic discovered

Answer 74

The first antibiotic discovered was in fact penicillin. It was first noted in 1928 by Alexander Fleming who discovered that mold (penicillium), growing on one of his culture plates, inhibited the growth of bacteria. It was not used clinically until 1940.

Question 75

How antibiotics act

Answer 75

Some antibiotics have a narrow spectrum of activity, meaning they are effective against a small group of bacteria. For example, some are only effective against gram positive bacteria; while others are only effective against gram negative bacteria. Other antibiotics may be effective against a larger group of microbes, usually both gram positive and gram negative microorganisms. These are called broad spectrum antibiotics.

A few bacteria have a predictable sensitivity pattern. For example, Pseudomonas is always resistant to the antibiotic ampicillin. Streptococcus pyogenes, the causative agent of Strept throat, is always (so far) sensitive to penicillin.

However, for most bacteria, an antibiotic susceptibility test is required to determine if the microbe is sensitive or resistant to various antibiotics.

Question 76

Antibiotic Susceptibility (Sensitivity) testing

Answer 76

Antibiotic Susceptibility (Sensitivity) testing is carried out in the laboratory to aid the physician in choosing an antibiotic for treatment.

The organism is first isolated and identified, then a susceptibility test is performed by spreading the organism evenly over the surface of an agar plate. Paper discs soaked in various antibiotics (indicated by abbreviations on the disc) are then placed on the plate, which is incubated over night.

The plate is examined, results recorded, interpreted and reported to the physician who determines which one should be used for treatment.

A clear area around a disc indicates that the organism is susceptible (sensitive) to it. If the bacteria grow right up to the disc, it is resistant (insensitive) to that antibiotic and it should not be used.

Question 77

Antibiotic (Drug) Resistant Bacteria (ARO’s)
Also called Antibiotic Resistant Organisms (AROs)
Also called Multidrug Resistant Organisms (MDROs)

Answer 77

Organisms that have drug resistance patterns that severely limit the choice of effective antibiotic use.

Drug-resistant bacteria are bacteria that were previously treatable by the best antibiotic available (e.g., penicillin) but have now become resistant to that drug.

Treatment is now required with alternate (second-choice) antibiotics. This often presents problems because these drugs are not always as effective and may be more toxic and more costly. Patients with infections caused by these drug resistant bacteria must be isolated in the health care facility and precautions must be taken so the organisms do not establish a foothold in the institution.

Among the drug-resistant bacteria causing the most alarm in health care facilities are methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE). These strains of bacteria have been dubbed “super bugs” by the media, but they are no more virulent than regular Staphylococcus aureus or Enterococcus. However, infections with these bacteria are more difficult and expensive to treat. Clostridium difficile has also recently been termed a super bug.

Question 78

Modes of Resistance
Factors that contributed to the development of drug-resistant bacteria include:

Answer 78

Some organisms are naturally resistant to certain antibiotics, while being susceptible to others.

Factors that contributed to the development of drug-resistant bacteria include:

Over-prescription of antibiotics: More than 600 million prescriptions are written for antibiotics in Canada every year. Many of them are given for any hint of infection, whether it is proved to be bacterial in nature or not. Patients often demand antibiotics for colds, flu and sore throats that are caused by viruses against which antibiotics have no effect. When bacteria are continually faced with antibiotics, they become genetically tougher and resistant strains develop. Enzymes may evolve that can inactivate an antibiotic. For example, penicillinase can break bonds in the penicillin molecule, rendering it useless.

People often stop taking antibiotics when their symptoms fade but before all the bacteria are killed. This has led to survival of the strongest bacteria which have the best defenses.

Mutation: When a colony of bacteria is treated with an antibiotic, most of the microbes are killed. Sometimes, however, there is a microbe with a mutation that makes it resistant to the drug. Antibiotics attack harmless microbes as well as harmful ones. Some resistant mutations occur spontaneously.

Conjugation: Drug resistance from harmless bacteria may be transferred to harmful microbes. One microbe attaches itself to another and a tube is opened between them in a process called conjugation. A copy of the genes that make the microbe resistant can then be passed from one to the other. An illustration of conjugation is shown in the figure below.

Question 79

How do you know which antibiotic is effective?

Answer 79

Laboratory testing will indicate the antibiotics which may be effective for a particular patient.

Question 80

Examples of antibiotic resistant organisms (Super Bugs MRSA, VRE and C difficile)

Answer 80

Examples of bacteria commonly called “super bugs”, because they have a limited number of treatment options, include MRSA (methicillin Resistant Staphylococcus aureus),VRE (vancomycin resistant Enterococcus ) and C difficile.

Staphylococcus aureus is a common cause of a variety of infections such as cellulitis, skin abscesses and post-operative incision infections. It can also be harbored without causing disease in the nasal passages. MRSA is a strain of Staphylococcus aureus that is resistant to a number of antibiotics including methicillin.

Currently, most MRSA is spread in hospital or health care settings (called HA MRSA), though some spread in community settings does occur and is on the increase (called CA MRSA). Transmission is almost entirely by direct contact.

Question 81

Why should we try to prevent the spread of MRSA in a health care facility?

Answer 81

Experiences in United States hospitals, where MRSA is widespread, have shown that once established, MRSA is difficult to eradicate from an institution. This results in increased patient mortality (death), morbidity (illness), length of stay and cost of care.

Question 82

How can we prevent MRSA from being introduced and spread in a health care facility?

Answer 82

Identify cases - screen all patients who enter a health care facility, by collecting nasal and rectal swabs.
Isolate cases - a single room is preferable, but if not feasible, an individual who is infected/colonized with MRSA can be placed in the same room as other individuals with MRSA. Special isolation precautions apply.
Identify carriers amongst patients and staff - test patients and staff who have been in contact with a case prior to appropriate isolation. This is easily done by obtaining and culturing a nasal swab.
Eradicate MRSA from carriers - this is usually accomplished by a course of intranasal mupirocin (Bactroban), use of disinfectant soaps and special home laundering precautions. Special ‘decolonization’ clinics have been set up for non hospitalized patients.

Question 83

Will I be asked to leave my job if I am found to be an MRSA carrier?

Answer 83

Decisions regarding work status are made on a case-by-case basis. A health care worker, who is thought to have spread MRSA, may be asked to abstain from direct patient contact until eradication is achieved.1

Question 84

What is Vancomycin Resistant Enterococcus (VRE)?

Answer 84

Enterococcus is a bacterium found as normal flora in the bowel. If it causes an infection, it is likely to be a nosocomial urinary tract infection or septicemia, particularly in the elderly or patients whose immune systems are compromised. It is a low-grade pathogen and does not pose a threat to healthy individuals. Vancomycin-resistant strains of Enterococcus are often resistant to almost all available drugs, so if a patient has an infection with one of these strains, it may be untreatable and potentially fatal.

Like MRSA, most VRE is spread in hospital or health care settings. Transmission is by direct contact or indirect contact through contaminated equipment such as thermometers, stethoscopes, blood pressure cuffs, call buttons, telephones and computer keyboards. (Enterococcus can withstand variable degrees of heat and drying and can survive up to 7 days on surfaces.)

To control the spread of VRE in an institution, it is vital to restrict antibiotic use (vancomycin and certain other antibiotics that allow enterococci to proliferate) and employ rigorous hygienic measures including hand washing and decontamination of everything in the environment of the patient who is colonized with VRE. Patients with VRE are placed in isolation with special precautions.

Patients are screened for MRSA and VRE by collecting and culturing a nose and rectal swab. Open wounds and draining sites are also cultured. Patients and visitors are taught proper hand hygiene. If the culture(s) are positive, then the patient is placed in an appropriate room and isolation precautions are instituted. If the patient is known to be positive, precautions are instituted immediately. Always check in IPC (Infection Prevention and Control) manual for your institution.

Question 85

What is Clostridium difficile (CDAD)?

Answer 85

It is a spore forming organism that can be found in the normal intestine, where it does not generally cause a problem. However, in some cases, particularly following antibiotic therapy with vancomycin, the normal flora of the intestine is disrupted, which allows the spores to vegetate. These vegetative organisms produce a toxin which affects the intestinal wall with a range of responses from mild (toxic megacolon) to severe (ileus) and even death, particularly in the elderly.

The primary symptom is watery unformed stools. This is sometimes called Clostridium difficile associated disease (CDAD). Alcohol hand rubs may not be effective against the spores. Hand washing with disinfectant soap and water is recommended- especially during outbreaks.

Question 86

Miscellaneous Modes for Controlling Infection - Silver

Answer 86

Silver has antibacterial properties and has been used to control microbial growth by impregnating bandages, catheters and other indwelling devices. Silver has also been impregnated into clothing, when there are limited laundry facilities available (battlefield and hiking gear), as well as food preparation associated items such as cutting boards, counter tops and appliances.

Question 87

Phages

Answer 87

Some viruses can infect certain bacteria, reproduce within them, and ultimately bring about their destruction. This is a natural occurrence in nature, with the viruses being specific for only certain bacteria. They do not infect human or other animal cells.

Phages have been used for nearly a century in the former Soviet Union. The research into their use was dropped when antibiotics were developed in the mid 1940’s, but with the emergence of antimicrobial resistance there has been renewed interest for their use worldwide.

Question 88

Organization of IPC Programs

Answer 88

All health care facilities are required to monitor the incidence of institutional nosocomial infections. Action must be taken when:

Statistics show an increase in the total number of infections
There is an increase of infections in certain wards
There is a rise in infections with antibiotic resistant strains.
Most large institutes have an Infection Prevention and Control Department. With the emergence of new organisms and the realization of the costs involved with outbreaks, dedicated health care professionals, called Infection Prevention and Control Practitioners, are most often responsible for managing this area, however, in smaller institutions, there may be a group of volunteer health care professionals responsible for this.

Question 89

Infection Prevention and Control Practitioners -

general objectives are as follows:

Answer 89

Surveillance and analysis of nosocomial and other infections
Surveillance of antibiotic-resistant strains of bacteria
Investigate and control outbreaks
Implement and monitor preventative procedures, such as determining which patients require isolation
Education
Develop policies
Consult with government, health care facilities and community

Question 90

Epidemiology

Answer 90

Infection prevention and control practitioners work with epidemiologists. Epidemiology is the study of the incidence, sources and spread of disease.
Epidemiologists are responsible for collecting specimens, liasoning with laboratory, physicians, infection prevention and control practitioners, patients and public health officials. Epidemiologist play a key role in tracking and containing outbreaks of infections.