Chapter 13. Infections and Disease

Causes of Disease

Infection (pathogen invasion and growth), genetics, environmental factors, and abnormal immune responses.

Infection

Invasion and multiplication of pathogens within the body.

Signs

Objective findings that can be measured by a healthcare professional.

Examples of signs

Body temperature, blood pressure, heart rate, and respiratory rate.

Symptoms

Subjective experiences reported by the patient that cannot be directly measured.

Examples of symptoms

Nausea, pain, and loss of appetite.

Can symptom severity be rated?

Yes, patients may rate symptoms (1-10), but this remains subjective rather than an objective measurement.

Normal body temperature

37°C (98.6°F).

Normal heart rate

60-100 beats per minute (BPM).

Normal respiratory rate

12-18 breaths per minute.

Normal blood pressure

90/60 to 120/80 mm Hg.

Why are vital signs important?

Changes from normal may indicate disease.

Syndrome

A recognizable collection of signs and symptoms that consistently occur together and indicate a specific disease or condition.

Communicable disease

A disease that spreads from one person to another.

Examples of communicable diseases

COVID-19, influenza, malaria.

Contagious disease

A disease that spreads easily from person to person.

Difference between communicable and contagious

Communicable means transmissible; contagious means easily transmissible.

Infectious disease

A disease caused by a pathogen.

Examples of infectious disease agents

Viruses, bacteria, fungi, and parasites.

Iatrogenic disease

Disease caused by a medical procedure or treatment.

Example of an iatrogenic disease

Surgical complication resulting in infection.

Nosocomial disease

An infection acquired in a healthcare facility that was not present upon admission.

Example of a nosocomial disease

Surgical site infection after hospitalization.

Zoonotic disease

An infectious disease transmitted from animals to humans.

Examples of zoonotic diseases

Rabies, Salmonella infections, and parasitic diseases.

Noncommunicable disease

A disease that cannot spread from person to person.

Examples of noncommunicable diseases

Diabetes, heart disease, cancer, asthma, and Alzheimer's disease.

Five periods of disease

Incubation, prodromal, illness, decline, and convalescence.

Incubation period

Pathogen enters and multiplies while the patient has no symptoms.

Prodromal period

Early, mild signs and symptoms appear as the pathogen multiplies.

Illness period

Signs and symptoms become most severe.

Decline period

Pathogen numbers decrease and symptoms begin to improve.

Convalescence

Recovery period when normal body function returns.

What affects the length of illness?

Pathogen type, immune response, and treatment.

Acute disease

A disease with rapid onset and short duration.

Example of an acute disease

Influenza.

Latent disease

A disease in which the pathogen remains dormant before reactivating.

Examples of latent diseases

Chickenpox (varicella-zoster), Epstein-Barr virus, and herpes simplex virus.

Koch's postulates

Principles stating that a specific pathogen causes a specific disease.

Pathogenicity

The ability of a microorganism to cause disease.

Virulence

The degree or severity of a pathogen's ability to cause disease.

High-virulence pathogen

A pathogen capable of causing severe disease, even in healthy individuals.

Examples of highly virulent pathogens

Ebola virus and Bacillus anthracis.

Median infectious dose (ID50)

The number of pathogen cells required to infect 50% of exposed hosts.

Primary pathogen

A pathogen capable of causing disease in healthy individuals.

Example of a primary pathogen

Certain strains of Escherichia coli.

Opportunistic pathogen

A pathogen that causes disease when host defenses are weakened.

Examples of opportunistic pathogens

Staphylococcus epidermidis and Candida albicans.

Stages of pathogenesis

Exposure, colonization, invasion, and infection.

Exposure stage

Microbes contact and adhere to body surfaces.

Colonization stage

Microbes establish themselves on body surfaces.

Invasion stage

Pathogens cross body defenses and enter sterile tissues.

Infection stage

Pathogens multiply within tissues.

Microbiota

Normal microorganisms that live on or in the body without causing disease.

Major ports of entry for pathogens

Respiratory tract, gastrointestinal tract, and genitourinary tract.

Focal infection

A localized infection that spreads microorganisms or toxins to another body site.

Example of a focal infection

A skin infection spreading into the bloodstream.

Systemic infection

An infection that spreads throughout the entire body.

Ports of exit

Skin, respiratory tract, gastrointestinal tract, and genitourinary tract.

Examples of pathogen exit

Sweat, coughing, sneezing, urination, and defecation.

Etiology

The study of the causes or origins of disease.

Epidemiology

The study of disease distribution, transmission, and control within populations.

Main goal of epidemiology

Recognize and control disease outbreaks.

Morbidity

The number or rate of people affected by a disease.

Prevalence

The total number or proportion of existing cases of a disease at a specific time.

Incidence

The number of new cases occurring during a specified time period.

Mortality rate

The percentage or number of deaths caused by a disease in a population.

Endemic disease

A disease constantly present within a specific geographic region.

Epidemic disease

A disease occurring in higher-than-normal numbers within a region.

Pandemic disease

An epidemic that spreads worldwide.

Passive carrier

A person who carries pathogens without being infected and can transmit them.

Example of a passive carrier

A healthcare worker transferring bacteria between patients on contaminated gloves.

Active carrier

An infected individual capable of transmitting disease to others.

Asymptomatic carrier

An infected person who spreads disease without showing symptoms.

Vertical transmission

Direct transmission from mother to child during pregnancy, childbirth, or breastfeeding.

Example of vertical transmission

HIV transmission from mother to infant.

Indirect contact transmission

Disease spread through contaminated objects (fomites).

Fomite

An inanimate object capable of transmitting pathogens.

Vehicle transmission

Disease spread through contaminated food, water, or air.

Mechanical transmission

Pathogen carried by a vector without the vector becoming infected.

Biological transmission

Pathogen carried by a vector that becomes infected before transmitting the pathogen.