Chapter 15 – Diagnosing Infections

Specimen Collection

Accurate diagnosis of infections begins with proper specimen collection using aseptic technique to prevent contamination and ensure reliable laboratory results.

• Aseptic Technique: Prevents contamination of specimens and ensures accuracy.

• Common Specimens & Collection Methods:

  • Urine: Clean-catch midstream sample.

  • Sputum: Deep cough into sterile container (not saliva).

  • Blood: Sterile venipuncture.

  • Skin: Swab, scraping, or biopsy depending on infection.

Antibody-Based Testing

Antibody-based tests utilize the specificity of antibodies produced by B lymphocytes to detect pathogens or immune responses.

• Antibodies: Proteins produced by B cells that bind to specific epitopes on antigens.

• Specificity: Ability of a test to correctly identify those without disease (few false positives).

• Sensitivity: Ability of a test to correctly identify those with disease (few false negatives).

Diagnostic Testing Methods

Microbial identification uses phenotypic, genotypic, and immunologic methods.

• Phenotypic Methods: Identify microbes by physical or biochemical traits.

  • Examples: Gram stain, culture, selective/differential media, biochemical tests, API strips, electron microscopy, antibiotic susceptibility tests.

• Genotypic Methods: Detect microbial DNA or RNA.

  • Examples: PCR, RT-PCR, FISH, hybridization, DNA probes, whole-genome sequencing, microarrays.

• Immunologic Methods: Use antigen-antibody reactions.

  • Examples: ELISA, indirect ELISA, Western blot, agglutination, fluorescent antibody testing, lateral flow tests, immunochromatography.

PCR vs. Antigen Tests

Comparison of nucleic acid amplification and antigen detection for viral diagnosis.

Coagulase Test

A biochemical test to differentiate Staphylococcus aureus (coagulase positive) from other staphylococci (coagulase negative).

• Positive: Staphylococcus aureus

• Negative: Staphylococcus epidermidis, Staphylococcus saprophyticus

Antibody Titers

Antibody titer is the highest dilution of serum that still yields a positive reaction, indicating antibody concentration.

• Higher titer (e.g., 1:256) = more antibodies present.

Matching Review

Chapter 16 – Infectious Diseases of the Skin & Eyes

Skin Lesions

Skin lesions are classified by appearance and content, aiding in diagnosis.

Important Skin and Eye Diseases

• Rubella: German measles; mild rash, dangerous in pregnancy.

• Ringworm (Tinea): Fungal infection (dermatophyte); circular, itchy rash.

• Impetigo: Caused by Staphylococcus aureus or Streptococcus pyogenes; honey-colored crusts.

• Cellulitis: Deep skin infection, usually Staphylococcus aureus; red, warm, swollen, painful.

• Shingles: Reactivation of varicella-zoster virus; painful, unilateral rash along a dermatome.

• Leishmaniasis: Protozoan infection via sand fly; skin ulcers.

• Smallpox: Caused by variola virus; eradicated, highly contagious, bioterrorism concern.

Clinical Scenarios

• Tree Branch Wound: Think sporotrichosis ("rose gardener's disease").

• Unilateral Facial Rash: Think shingles.

• "Slapped Cheek" Rash: Think fifth disease (parvovirus B19).

Chapter 17 – Nervous System Infections

Meningitis

Meningitis is inflammation of the meninges, presenting with fever, headache, neck stiffness, photophobia, and confusion.

• Most serious acute bacterial cause: Neisseria meningitidis

• Neonatal meningitis: Streptococcus agalactiae (Group B Strep), Escherichia coli

• Diagnosis: Lumbar puncture for CSF analysis

Poliomyelitis

• Cause: Poliovirus

• Symptoms: Muscle weakness, paralysis

Arboviruses

Arboviruses are transmitted by arthropods (e.g., mosquitoes).

• Examples: West Nile virus, Eastern Equine Encephalitis, St. Louis Encephalitis

Creutzfeldt-Jakob Disease

• Cause: Prions (infectious proteins)

• Characteristics: Rapid dementia, fatal, no inflammation

Chapter 18 – Cardiovascular & Lymphatic Diseases

Ebola Virus Disease

• Transmission: Body fluids

• Disease: Hemorrhagic fever

Important Terms

• Viremia: Virus in the bloodstream

• Bacteremia: Bacteria in the bloodstream (may be temporary)

• Septicemia: Serious bloodstream infection causing systemic illness

Diseases & Transmission

Rocky Mountain Spotted Fever

• Classic symptom: Rash begins on wrists/ankles, spreads inward

HIV Case Study

• Horizontal Transmission: Sexual contact, blood, needle sharing

• Vertical Transmission: Mother to child (pregnancy, birth, breastfeeding)

• Prevention: Safe sex, condoms, PrEP, blood screening, needle safety, antiretroviral therapy during pregnancy

Mixed Chapter Matching

Diseases & Transmission

Signs & Symptoms

Written Response Topics

Why Would a Sudden Smallpox Outbreak Be Surprising?

• Smallpox was eradicated in 1980; no natural cases exist today.

• Most people are no longer vaccinated.

• An outbreak would spread rapidly and could indicate accidental release or bioterrorism.

Salk vs. Sabin Polio Vaccines

High-Yield Memorization List

• Staphylococcus aureus → Coagulase positive

• Neisseria meningitidis → Acute bacterial meningitis

• Streptococcus agalactiae → Neonatal meningitis

• Yersinia pestis → Plague

• Francisella tularensis → Tularemia

• Brucella spp. → Brucellosis

• Bartonella henselae → Cat scratch disease

• Rickettsia rickettsii → Rocky Mountain spotted fever

• Varicella-zoster virus → Shingles

• Poliovirus → Poliomyelitis

• Variola virus → Smallpox

• Parvovirus B19 → Fifth disease ("slapped cheek")

• Leishmania spp. → Leishmaniasis

• Prions → Creutzfeldt-Jakob disease