Ch. 6: Transmission of Infection, the Compromised Host, and Epidemiology

• Contact (direct, indirect, and droplet)
• Vehicle
• Vector

• Transmitted directly from person to person through touching, kissing, sexual interation, etc.
• Diseases: Hepatitis A, Smallpox, Staphylococcal infections, Mononucleosis, Sexually transmitted diseases.

• Takes place through intermediates that are usually non-living articles
• For example: Tissues, Handkerchiefs, Towels Bedding, Contaminated needles (the latter easily transferring HIV and hepatitis B).
• - Non-living intermediates that act as agents of transmission in indirect contact are referred to as fomites.

• Example are sneezing, coughing etc.
• Droplets spread 3 to 6 feet

• Vehicle transmission involves pathogens riding along on supposedly clean components.
• Examples of vehicles include: Air, Food, Water, Blood, Bodily fluids, Drugs
• The “vehicle” is usually air, can also be a fomite
• When food transmits pathogens as a vehicle and it makes us sick, this is what we think of as food poisoning.
• Dust (which contains HUGE numbers of microbes) uses the air to travel from host to host.

• Pathogens are transmitted by carriers (usually associated with some disease), and usually arthropods like Fleas, Ticks, Flies, Lice, Mosquitoes
• There are two types of vector transmission: mechanical and biological

• Pathogens are on vector’s body parts and are passively brushed off and onto the host
• An example of this is house flies who commonly frequent fecal material, get the pathogens on their feet, wings, etc, and pass it to a host by when they land on them or their food.

• Pathogens are within the vector and transmission to the host is through a bite
• Example: mosquitoes carrying plasmodium (malaria organism) and the West Nile virus.

• Age: The elderly have decreased immunity making them more susceptible to disease
• Gender: Men are more susceptible to pneumonia, women are more susceptible to UTIs due to structural features
• Lifestyle
• Occupation: organisms you are exposed to at work (ex- daycare workers, nurses, etc are going to be exposed to a larger variety of pathogens)
• Emotional State: Having high stress can weaken your immune system making you more susceptible to disease
• Climate: Different bacteria thrive in different climates

• Neutropenia is a lower than normal number of neutrophils in the blood
• Neutrophils are a form of primary phagocytic defense and an important component of a host’s innate immune response.
• The most common cause of profound neutropenia is the administration of cytotoxic chemotherapy for the treatment of malignant tumors seen in cancer.
• Neutropenia usually disappears when chemotherapy ends
• In neutropenia, because there aren’t enough neutrophils to fight off infections, bacterial and fungal infections develop.
• Neutropenic patients are also at risk with any invasive surgical procedure and whenever an indwelling catheter is necessary
• Gram-negative bacteria from either the patient’s colon or the nvironment cna cause life-threatening issues in neutropenic patients.
• Gram-positive pathogens like staph and strep can cause infections originating in either blood stream or central venous catheter.

Bacterial infections can begin to develop as soon as the neutorophil level decreases.

Fungal infections ocurr only in people who have been neutropenic for long periods.

Burn patients are more at risk because they have lost large portions of their primary level of defense (the skin)

• The number one bacterial concern is pseudomonas aeruginosa because this organism is very resistant to methods used to control bacterial growth, such as antiseptics and disinfectants.
• Burn patients are also very susceptible to fungal infections

• The urinary tract
• The respiratory tract
• Surgical wounds

• IV application
• Invasive tests
• Surgery
• Catherization

The most common pathogen for nosocomial infections is staphlococcus aureus. After that is just generally other pathogens and after that is E. Coli. These organisms are always in hospitals and are easily moved from place to place. Alot of organisms that cause nosocomial infections are now resistant to antibiotics such as MRSA and VRSA

• These pathogens can be part of the normal flora in our bodies.
• Pathogens move from their “normal home” to somewhere else in the body.
• Pathogens expand their numbers beyond a “safe” amount
• This can happen in response to antibiotics. Example: Antibiotics can kill bacteria in the intestines, leaving a lot of room. If there’s a little bacteria which could be harmful but is considered normal flora when its in its appropriate small amount and it grows (because it has all this space) it can become infectious, taking advantage of its opportunity.

The number of new cases contracted within a set population in a specific period. This info provides us with a reliable indication of the spread of a particular disease.

Defined as the total number of people infected within a population at any given time. Prevalence data can be used to measure how seriously and for how long a particular disease affects the population

The number of individuals affected by the disease during a set period divided by the total population.

The number of deaths due to a specific disease during a specific period divided by the total population.

Occuring in random manner; no threat to public health

Diseases that are constantly in the population

Incidence of a disease suddenly higher than expected, morbidity and mortality rates may increase, this may become a more widespread public health problem.

World-wide epidemic

• It arises from contact with contaminated substances, most commonly water contaminated with fecal material or improperly prepared food.
• It affects a large numbers of people.
• It subsides quickly when the contamination is dealt with.

• It is amplified by person to person contact
• It remains in the population for a long time
• It is more difficult to deal with than a common source outbreak.

The study of the factors and mechanisms involved in the frequency and spread of diseases or other health-related problems, and is an important part of our understanding of the disease.