Final Exam Key Concepts: Infections, Immunity, and Epidemiology
Superinfections and the Human Microbiome
What are superinfections?
A secondary infection that occurs when the normal microbiota are disrupted, allowing opportunistic pathogens to establish infection.
What is the human microbiome? How does it affect overall health?
The community of microbes (bacteria, fungi, viruses) living on and inside the human body.
Influences health by modulating immunity, metabolism, and barrier defenses; contributes to homeostasis and resistance to colonization.
Ways in which we acquire microbes that become part of our 'normal biota'
Direct and close contact with people or animals
Environmental exposure (surfaces, shared environments)
Birth and early life colonization
Diet and ongoing exposure over time
Repeated exposures leading to stable colonization
Areas of the body where microbes are known to be present
Skin and its folds; eyes; oral cavity; upper and lower respiratory tract; gastrointestinal tract; genitourinary tract; external ear canal; other mucosal surfaces.
Difference between infection and disease
Infection: invasion and multiplication of microbes in the host.
Disease: the host's tissue damage or dysfunction resulting from infection (symptoms and signs).
Why polymicrobial infections are concerning
Involve multiple pathogens, increasing virulence and complexity.
Can complicate diagnosis and treatment; potential for synergistic damage and increased resistance.
The 5 steps leading to infection and disease
Portal of entry
Attaching to host cell/tissue
Surviving host defenses
Causing disease (pathogenesis)
Portal of exit
Virulence, pathogenicity, and pathogenesis
Virulence: degree of damage a pathogen can inflict on the host; how severe disease can be.
Pathogenicity: ability of an organism to cause disease.
Pathogenesis: the mechanism by which a disease develops.
Endotoxin vs exotoxin
Endotoxin: a component (lipopolysaccharide) of the outer membrane of gram-negative bacteria; often associated with fever and shock.
Exotoxin: a toxin secreted by bacteria (often gram-positive); can have high specificity and potent effects.
Patterns of infection (table 11.3) and related concepts
Key ideas include latency and sequelae (long-term consequences after infection).
Patterns may include acute, chronic, latent, persistent, or recurrent infections depending on organism and host.
Definition of sign, symptom, syndrome, subclinical/asymptomatic
Sign: objective evidence of disease (observed by clinician).
Symptom: subjective experience reported by the patient.
Syndrome: a group of signs and symptoms that occur together and characterize a condition.
Subclinical/Asymptomatic: infection or disease without noticeable symptoms.
The course of infection: the stages
Incubation period
Prodromal stage
Acute phase
Convalescent period
Continuation period
Reservoir, transmitter, and carrier definitions
Reservoir: any person, animal, or environmental source where a pathogen resides and multiplies.
Transmitter: an agent that conveys a pathogen from reservoir to host.
Carrier: a person who harbors and can transmit a pathogen without symptoms.
What is zoonosis?
An infection that is naturally transmitted from animals to humans.
Modes of transmission of infections/diseases
Direct transmission: person-to-person contact (e.g., touching, kissing, sexual contact).
Indirect transmission: via a vehicle (fomites, food, water) or via an intermediate host.
Mechanical transmission: transmission by a nonbiological vector (e.g., contaminated hands, clothing).
Biological transmission: transmission via an arthropod or other vector in which the pathogen completes part of its life cycle.
Nosocomial Infections, Epidemiology, and Core Concepts
What are nosocomial infections? What are the top 3 nosocomial infections?
Infections acquired in a hospital or healthcare setting.
Common top ones include urinary tract infections, surgical site infections, and pneumonia (ventilator-associated or hospital-acquired).
Koch's postulates: purpose and steps
Purpose: establish a causal relationship between a microbe and a disease.
Steps:
1) Find the microorganism in all cases of the disease but not in healthy hosts.
2) Isolate the microorganism in culture.
3) Reproduce the disease when a susceptible host is inoculated with the organism.
4) Re-isolate the microorganism from the experimental host.
Prevalence vs incidence in epidemiology
Incidence: rate of new cases in a defined population over a period of time.
Prevalence: total number of existing cases (new and old) in a defined population at a given time.
Definitions: epidemiology, epidemic, endemic, sporadic, pandemic
Epidemiology: study of the distribution and determinants of diseases in populations.
Epidemic: a sudden increase in cases above what is normally expected in a population.
Endemic: disease consistently present but at a relatively stable level in a population.
Sporadic: occasional cases at irregular intervals.
Pandemic: an epidemic that spreads across a large geographic area, often worldwide.
Immunity and Host Defenses (referenced material in Module 5)
Overview: immunity and host defenses basics are provided in two summary documents.
For each organ-system disease chapter, know:
Basic anatomy and physiology
Host defenses and microbiota (if any)
For each listed disease, know cause, signs/symptoms, transmission, epidemiology, prevention, and treatment as per Disease Tables.
Chapter 16: Diseases of the Skin and Eyes (Key Disease Profiles)
MRSA (Methicillin-resistant Staphylococcus aureus)
Cause: MRSA strains of Staphylococcus aureus
Signs & symptoms: skin infections that may appear as boils, abscesses, or cellulitis; may be resistant to beta-lactam antibiotics
Transmission & epidemiology: direct contact, healthcare or community settings; high concern due to resistance
Prevention & treatment: hygiene measures; targeted antibiotics based on susceptibility; decolonization strategies as appropriate
Measles
Cause: Measles virus
Signs & symptoms: fever, cough, conjunctivitis, Koplik spots, generalized rash
Transmission & epidemiology: highly contagious; airborne transmission
Prevention & treatment: vaccination (MMR); supportive care; vitamin A in some cases
Impetigo
Causes: Staphylococcus aureus and/or Streptococcus pyogenes
Signs & symptoms: vesicles, pustules that crust; contagions common in children
Pathogenesis & virulence: skin barrier breach with superficial infection
Transmission & epidemiology: contact transmission; common in crowded settings
Prevention & treatment: topical/systemic antibiotics; hygiene
Chickenpox/Shingles (Varicella-Zoster Virus)
Cause: Varicella-zoster virus (VZV)
Signs & symptoms: varicella (rash with lesions in various stages); herpes zoster (painful dermatomal rash)
Transmission & epidemiology: airborne and direct contact with lesions
Prevention & treatment: vaccination; antiviral therapy in some cases; symptom management
Ringworms (Tinea infections)
Overview: fungal infections of skin/hair/nails; common species vary by site
Note: common Tinea infections are listed in Table 16.1; reviewing that table suffices
Conjunctivitis
Causes: bacterial or viral etiologies
Signs & symptoms: redness, discharge, irritation
Transmission & epidemiology: contact/transmission via contaminated hands or objects
Prevention & treatment: hygiene, targeted antimicrobial therapy depending on etiology
Chapter 17: Diseases of the Nervous System
Meningitis
Cause: primarily Neisseria meningitidis (also other bacteria/viruses present in broader contexts)
Signs & symptoms: acute onset of fever, headache, neck stiffness, photophobia; altered mental status
Culture & Table 17.1: diagnostic and epidemiologic details provided in Table 17.1
Diagnosis, transmission & epidemiology, prevention & treatment: per table guidelines; vaccination and antibiotics as indicated
Neonatal Meningitis
Causes, signs & symptoms, culture & diagnosis, transmission & epidemiology, prevention & treatment: per Disease Table 17.2
Acute vs Subacute Encephalitis
Causes, signs & symptoms, transmission & epidemiology, prevention & treatment: refer to Tables 17.6 and 17.7
Rabies
Cause, signs & symptoms, transmission & epidemiology, prevention & treatment: refer to Table 17.8
Tetanus
Cause, signs & symptoms, transmission & epidemiology, prevention & treatment: refer to Table 17.9
Botulism
Know the 3 types: per Table 17.2 (foodborne, wound, infant)
Chapter 18: Systemic Infections
Malaria
Causes, signs & symptoms, transmission & epidemiology, prevention & treatment: per Disease Table 18.1
Sepsis
Causes, signs & symptoms, transmission & epidemiology, prevention & treatment: per Disease Table 18.4
Lyme Disease
Cause, signs & symptoms, transmission & epidemiology, prevention & treatment, sequelae: per Disease Table 18.7
Chapter 19: Respiratory and Related Infections
Pharyngitis
Causes, signs & symptoms, pathogenesis, culture & diagnosis, transmission & epidemiology, prevention & treatment: per Table 19.1
Acute Otitis Media
Causes, signs & symptoms, transmission & epidemiology, prevention & treatment: per Table 19.4
Community-Acquired vs Hospital-Associated Pneumonia
Causes, signs & symptoms, transmission & epidemiology, prevention & treatment: per Tables 19.5 and 19.6
Respiratory Syncytial Virus (RSV)
Cause, signs & symptoms, transmission & epidemiology, prevention & treatment: per Table 19.9
Tuberculosis
Cause, signs & symptoms, diagnosis, pathogenesis, transmission & epidemiology, prevention & treatment
Differences to know: primary, secondary, and extrapulmonary TB
Chapter 20: Digestive System Infections
Acute Diarrhea
Causes: primarily Campylobacter jejuni and Clostridioides difficile (C. difficile) [truncated reference in transcript]
Signs & symptoms, transmission & epidemiology, prevention & treatment: per Table 20.1
Chronic Diarrhea
Causes: primarily Escherichia coli
Signs & symptoms, transmission & epidemiology, prevention & treatment: per Table 20.3
Gastritis and Gastric Ulcers
Cause, signs & symptoms, transmission & epidemiology, prevention & treatment: per Table 20.7
Hepatitis (A, B, C, D, E)
Cause, signs & symptoms, transmission & epidemiology, prevention & treatment: per Table 20.8
Also know which ones have the highest prevalence associated with liver cancer in the United States versus worldwide
Chapter 21: Genitourinary and Reproductive Infections
Urinary Tract Infections (UTIs)
Cause, signs & symptoms, transmission & epidemiology, prevention & treatment: per Table 21.1
Discharge Disorders (Gonorrhea and Chlamydia)
Cause, signs & symptoms, transmission & epidemiology, prevention & treatment: per Table 21.3
Trichomoniasis
Cause (Trichomonas vaginalis), signs & symptoms, transmission & epidemiology, prevention & treatment: per Table 21.4
Syphilis
Primary, secondary, latent/tertiary, congenital
Cause, signs & symptoms, transmission & epidemiology, prevention & treatment: per Table 21.6
Notes and study tips
Review the two immunity summary documents in module 5 for a consolidated overview of host defenses.
For chapters 16–21, use the Disease Tables as the primary reference for disease-specific details (cause, signs & symptoms, transmission, epidemiology, prevention, treatment).
Understand the distinctions among infection, colonization, latency, and sequelae, and how each affects clinical outcomes and epidemiology.
Be able to explain how antibiotic use can influence superinfections and microbiome balance, and why nosocomial infections require stringent infection-control practices.
Be prepared to differentiate direct vs indirect, mechanical vs biological transmission, and to apply Koch’s postulates to hypothetical scenarios.
Understand how prevalence and incidence inform public health assessments and resource allocation.
Be able to discuss ethical and practical implications of infectious disease control, vaccination programs, antibiotic stewardship, and patient education.
Date reference: 8/28/25