Focus: Understanding disease terminology and how diseases impact health.
Subsections:
Terminology in epidemiology and disease classification
Pathogenesis: Mechanisms of how diseases cause illness
Normal Microbiota
Definition: Microorganisms that normally inhabit various body sites without causing disease.
Development:
Normal microbiota begins to establish at birth and is typically well-established by age three.
High concentration of normal microbiota is found in the colon, primarily like E. coli and species from the Enterobacteriaceae family (e.g., Klebsiella, Enterobacter).
Other examples include Clostridium species, including C. difficile.
Gastrointestinal Tract Normal Microbiota
Increased numbers transitioning from the small intestine to the colon.
Different bacteria types are prevalent in the colon:
Obligate anaerobes (e.g., Bacteroides)
Facultative anaerobes (e.g., E. coli)
Other body sites include:
Genital and urinary tract:
Bladder: Sterile; normal microbiota present at the urethra.
Common microorganisms:
Women: Lactobacillus, Streptococcus, Candida
Men: Mycobacterium smegmatis
Skin and eyes: Staphylococcus and Malassezia (a filamentous fungus).
Areas Considered Sterile
Accessory gastrointestinal organs: liver, gallbladder, pancreas (should be sterile).
Brain and related tissues are also considered sterile.
Opportunistic Infections
Definition: Situations where normal microbiota become pathogenic.
Shift in location or overpopulation causes infections:
Example 1: Streptococcus pneumoniae from oral cavity to alveoli causes typical pneumonia.
Example 2: E. coli present in the gut leading to a bladder infection when it moves into the urinary tract.
Overgrowth scenarios:
Changing location within the body (common).
Immunocompromised states (e.g., steroid inhalers leading to oral thrush).
Alteration in the environment, such as antibiotic use leading to C. difficile overgrowth due to the elimination of competition.
Epidemiology Terms
Endemic: Disease consistently present in a specific location, e.g., Lyme disease in Maryland.
Epidemic: Occurrence of disease above normal/expected levels in a specific area, e.g., seasonal flu outbreaks, scarlet fever epidemic.
Pandemic: Epidemic that has spread globally, e.g., COVID-19 and H1N1 (swine flu).
Basics of Epidemiology
Definition: Study of distribution and determinants of health-related states in specified populations.
Tools: Maps, statistics, modeling, and door-to-door data collection.
Example of Epidemiological Work
John Snow's cholera map (1854) was a critical development in public health.
Observed cholera cases concentrated around a pump on Broad Street; identified it as a source of infection leading to public health interventions.
Reportable Diseases
Healthcare providers must report certain diseases to state health departments and the CDC.
Categories include:
Communicable and contagious diseases like measles, chickenpox, mumps, HIV/AIDS, and syphilis.
Variability in notification is based on the disease's public health significance.
Key Terminology in Infectious Diseases
Acute Disease: Rapid onset and severe symptoms; usually resolves quickly or leads to death.
Chronic Disease: Develops slowly with mild symptoms, persist over time.
Asymptomatic: Infected but showing no symptoms, can still transmit the disease temporarily.
Communicable: Disease that can be transmitted between individuals.
Contagious: A subset of communicable diseases that spread easily between individuals.
Primary Infection: First instance of infection, e.g., chickenpox.
Secondary Infection: Follows a primary infection; usually involves normal microbiota taking advantage of a weakened immune system, e.g., sinusitis after a cold.