Domain 2.15Anatomy and Physiology

Common Infectious Diseases

Last updated June 16, 2026

Overview

Welcome to your study guide for Common Infectious Diseases. As a Medical Assistant (MA), you play a frontline role in infection control. You are often the first person to gather a patient's history, the one who collects the specimens for testing, and the professional responsible for sanitizing the room afterward to prevent spread.

Why This Matters:

  • Occupational Safety: You must understand how diseases are transmitted (bloodborne vs. droplet) to select the correct Personal Protective Equipment (PPE) and protect yourself.
  • Patient Education: You will reinforce provider instructions regarding medication compliance and preventing the spread of infection to partners or family members.
  • Public Health Reporting: Many of these diseases (like Gonorrhea, Syphilis, and HIV) are Notifiable Diseases, meaning positive results must be reported to the state health department/CDC.

This guide focuses on the specific infectious diseases most frequently tested on the CCMA exam, particularly Sexually Transmitted Infections (STIs) and bloodborne pathogens.

1. Microbiology: The Cells That Cause Disease

Not all cells in the body are human. Before diving into specific diseases, you must understand the cellular structure of pathogens. This knowledge helps you understand how antibiotics and vaccines work.

A. Bacteria (Prokaryotic Cells)

Bacteria are single-celled organisms that do not have a nucleus. They are treated with Antibiotics.

  • Classification by Shape:
    • Cocci: Round/Spherical.
    • Bacilli: Rod-shaped.
    • Spirilla/Spirochete: Spiral-shaped (e.g., Treponema pallidum causes Syphilis; Borrelia burgdorferi causes Lyme disease).
  • Classification by Arrangement:
    • Staphylo-: Clusters (like grapes). Staphylococcus = Clusters of round bacteria.
    • Strepto-: Chains. Streptococcus = Chains of round bacteria.
    • Diplo-: Pairs. Diplococci.
  • Gram Staining:
    • Gram-Positive: Stains Purple.
    • Gram-Negative: Stains Pink/Red.

B. Viruses (Non-Cellular)

Viruses are NOT cells. They are strands of genetic material (DNA or RNA) wrapped in a protein coat.

  • Obligate Intracellular Parasites: They cannot reproduce on their own; they must invade a host cell and "hijack" its machinery to replicate.
  • Treatment: Antibiotics do NOT kill viruses. Antivirals or vaccines are used.

C. Fungi

Plant-like organisms (Eukaryotic) that absorb nutrients from organic matter.

  • Yeasts: Single-celled.
  • Molds: Multi-celled.
  • Common Infection: Candida albicans (Yeast infection/Thrush).

D. The Chain of Infection

To stop a disease, you must break the chain (e.g., washing hands breaks the "Mode of Transmission").

  • Pathogen: A microorganism that causes disease.

2. Sexually Transmitted Infections (Bacterial)

Bacterial STIs are very common. The key for the exam is to differentiate their symptoms and know the complications if left untreated.

A. Chlamydia

  • Pathogen: Chlamydia trachomatis (Bacteria).
  • Overview: The most common reportable bacterial STI in the United States. It is often called the "Silent Infection" because many people have no symptoms.
  • Key Signs & Symptoms:
    • Dysuria (painful urination).
    • Abnormal discharge from the penis or vagina.
    • If untreated: Can spread to the reproductive organs.
  • Complications:
    • Pelvic Inflammatory Disease (PID) in females, which can damage the fallopian tubes and lead to infertility.
  • Diagnostic Tests: Urine sample or vaginal/urethral swab (Nucleic Acid Amplification Test - NAAT).
  • Treatment: Antibiotics (typically Azithromycin or Doxycycline).
  • MA Role: Advise patients to abstain from sexual activity until treatment is complete and to notify partners.

Exam Tip: Think "Chlamydia is Cloaked." It is often silent (asymptomatic), hiding until it causes damage like infertility.

B. Gonorrhea

  • Pathogen: Neisseria gonorrhoeae (Bacteria).
  • Overview: A bacterial infection that grows easily in warm, moist areas of the reproductive tract.
  • Key Signs & Symptoms:
    • Men: Thick, yellow-green discharge from the penis and severe dysuria.
    • Women: Increased vaginal discharge, dysuria, or bleeding between periods.
    • Can also infect the rectum, throat, and eyes.
  • Diagnostic Tests: Urine sample or swab (culture or NAAT).
  • Treatment: Antibiotics (typically an injection of Ceftriaxone).
  • MA Role: Be aware of "co-infection." Patients with Gonorrhea are frequently tested/treated for Chlamydia at the same time.

Mnemonic: Gonorrhea makes the urine feel like it's Gone through a razor blade (severe burning) and produces Green discharge.

C. Syphilis

  • Pathogen: Treponema pallidum (A Spirochete bacterium).
  • Overview: A systemic infection that progresses in distinct stages. It is known as "The Great Imitator" because its symptoms look like many other diseases.
  • Progression and Symptoms:
    1. Primary Stage: Appearance of a Chancre (a firm, round, painless sore) at the infection site.
    2. Secondary Stage: Skin rashes (often on the palms of hands and soles of feet) and mucous membrane lesions.
    3. Latent Stage: No visible signs.
    4. Tertiary Stage: Severe damage to internal organs, including the brain (Neurosyphilis), nerves, eyes, and heart.
  • Diagnostic Tests: Blood tests (VDRL or RPR) to detect antibodies.
  • Treatment: Penicillin G (usually administered as an intramuscular injection).
  • MA Role: Observe injection safety protocols. Since syphilis can be congenital (passed from mother to baby), pregnant women are routinely screened.
Infection Key Feature Pathogen Type
Chlamydia "Silent," leads to infertility/PID. Bacteria
Gonorrhea Yellow-green discharge, severe dysuria. Bacteria
Syphilis Painless Chancre, rash on palms/soles. Bacteria (Spirochete)

3. Viral Infections Affecting the Immune System

These conditions are viral, meaning antibiotics are ineffective. Management focuses on antivirals or supportive care.

A. Human Immunodeficiency Virus (HIV) and AIDS

  • Pathogen: Human Immunodeficiency Virus (Retrovirus).
  • Pathophysiology: The virus attacks the body's immune system, specifically destroying CD4 T-cells (helper T-cells). This leaves the body vulnerable to opportunistic infections.
  • Transmission: Contact with infected blood, semen, vaginal fluids, or breast milk. NOT spread by casual contact.
  • Stages:
    1. Acute Infection: Flu-like symptoms shortly after infection.
    2. Clinical Latency: Virus reproduces at low levels; patient may have no symptoms.
    3. AIDS (Acquired Immunodeficiency Syndrome): The most severe phase.
  • Key Diagnostic Findings (High Yield):
    • Screening: Antigen/Antibody immunoassays.
    • Diagnosis of AIDS: Occurs when the CD4 T-cell count drops below 200 cells/mm³.
  • Treatment: Antiretroviral Therapy (ART). This does not cure HIV but suppresses the virus to undetectable levels, preventing transmission ("Undetectable = Untransmittable").
  • MA Role: Strict adherence to Standard Precautions and HIPAA. HIV status is highly sensitive protected health information (PHI).

Exam Tip: Remember the number 200. HIV becomes AIDS when the CD4 count is < 200.

B. Mononucleosis ("Mono")

  • Pathogen: Epstein-Barr Virus (EBV).
  • Overview: Often called the "Kissing Disease."
  • Transmission: Direct contact with saliva. Common in adolescents and young adults.
  • Key Signs & Symptoms:
    • Extreme fatigue and malaise.
    • Fever and severe sore throat.
    • Swollen lymph nodes in the neck.
    • Splenomegaly: Enlarged spleen (located in the Left Upper Quadrant - LUQ).
  • Diagnostic Tests: Monospot test (blood test) to detect heterophile antibodies.
  • Treatment: Supportive care (rest, fluids, fever reducers). NO antibiotics (it is viral).
  • Critical MA/Patient Education: Patients must avoid heavy lifting and contact sports for 3-4 weeks.
    • Why? Because the spleen is enlarged and vulnerable to rupture, which is a life-threatening emergency.

4. Viral Hepatitis

Hepatitis is inflammation of the Liver (Located in the Right Upper Quadrant - RUQ). While there are several types, B and C are the most relevant for bloodborne pathogen training.

General Hepatitis Signs

  • Jaundice: Yellowing of the skin and whites of the eyes (sclera).
  • Dark Urine / Clay-Colored Stool: Indicates liver dysfunction/bile issues.
  • Lab Tests: Elevated liver enzymes (ALT and AST).

A. Hepatitis B (HBV)

  • Pathogen: Hepatitis B Virus.
  • Transmission: Contact with infectious Blood, semen, and other Body fluids. (Think B for Blood and Body fluids).
    • Can be transmitted via sexual contact, sharing needles, or from mother to baby.
  • Risk Factors: Healthcare workers (needlesticks), unprotected sex, IV drug use.
  • Treatment: Acute cases may resolve on their own. Chronic cases require antivirals.
  • Prevention (Critical for MAs):
    • The Hepatitis B Vaccine: OSHA requires employers to offer this vaccine series free of charge to any employee at risk of occupational exposure (like MAs) within 10 days of assignment.
    • The series usually consists of 3 shots.

B. Hepatitis C (HCV)

  • Pathogen: Hepatitis C Virus.
  • Transmission: Primarily through exposure to infected blood.
    • Think C for Circulation or Contaminated needles.
  • Risk Factors: Past or current injection drug use (sharing needles) is the most common risk factor. Also, blood transfusions before 1992.
  • Pathophysiology: HCV is more likely than HBV to become a chronic infection, leading to cirrhosis (scarring) or liver cancer.
  • Treatment: Unlike Hep B, there is no vaccine for Hep C. However, modern antiviral medications can now cure Hepatitis C in most people.

Comparison of Hepatitis Types

Type Transmission Vaccine Available? Mnemonic/Key Fact
Hep A Fecal-Oral (Food/Water) Yes A is for Anus (bowel movements).
Hep B Blood / Body Fluids Yes (OSHA Requirement) B is for Blood/Body fluids.
Hep C Blood (IV Drug Use) No C is for Chronic / Circulation.

5. Final Key Takeaways

  • Microbiology Basics:
    • Cocci = Round; Bacilli = Rod; Spirilla = Spiral.
    • Staphylo = Clusters; Strepto = Chains.
    • Gram-Positive = Purple; Gram-Negative = Pink.
    • Fungi = Eukaryotic (e.g., Candida).
  • Reportable Diseases: Gonorrhea, Chlamydia, Syphilis, HIV, and Hepatitis are legally required to be reported to health authorities.
  • OSHA Compliance: You must be offered the Hepatitis B vaccine free of charge by your employer.
  • Spleen Safety: A patient with Mono (EBV) has an enlarged spleen (LUQ) and must avoid contact sports to prevent rupture.
  • Syphilis Signs: Look for the keyword "Chancre" (painless sore) for primary syphilis.
  • Discharge Colors: Gonorrhea often presents with Green/Yellow discharge; Chlamydia is often asymptomatic.
  • HIV Metrics: The transition from HIV to AIDS is defined by a CD4 count < 200.
  • Liver Anatomy: Hepatitis affects the liver, found in the RUQ. Signs include Jaundice (yellow skin) and elevated ALT.
  • Treatment:
    • Bacteria (Chlamydia, Gonorrhea, Syphilis) = Antibiotics.
    • Viruses (HIV, Herpes, Mono, Hep B/C) = Antivirals or Supportive Care (Antibiotics do NOT kill viruses).