The 4 Infectious Disease Gold Standard Diagnoses Every FNP Student Must Know for Boards
Infectious Disease · 4 min read · October 19, 2026
Introduction
Infectious diseases show up everywhere on the AANP and ANCC board exams. From respiratory bugs to tick-borne illnesses, exam writers love to test whether you can connect a constellation of symptoms to the right diagnostic test and first-line treatment. Let us break down four high-yield infectious disease concepts you are guaranteed to see on test day, stripped of the fluff and focused purely on what matters for your boards and your future clinical practice.
1. Lyme Disease: Spotting the Bullseye and Knowing Your Tests
Lyme disease, caused by the spirochete Borrelia burgdorferi and transmitted by the blacklegged tick, is a board favorite. The hallmark sign is erythema migrans—the classic "bullseye" rash—which typically appears 7 to 14 days after a tick bite.
Board exams will test you extensively on the two-step serological testing protocol:
- Step 1: Perform an Enzyme Immunoassay (EIA) or Immunofluorescence Assay (IFA).
- Step 2: If the EIA or IFA is positive or equivocal, follow up with a Western blot test.
Clinical Pearl: Do not wait for lab results to treat a patient presenting with an early erythema migrans rash and a history of exposure in an endemic area. Serology can be falsely negative in the first few weeks because antibodies take time to develop. Treatment is clinical: Doxycycline 100 mg BID for 10 to 21 days is the gold standard for adults and children over 8 years old. (Remember: alternatives for pregnant women or children under 8 include amoxicillin).
2. Group A Streptococcal Pharyngitis: Centor Criteria and Preventing Complications
When a patient walks in with a sore throat, your clinical brain must immediately shift to ruling out Group A Streptococcus (Streptococcus pyogenes). Board questions will often give you a clinical scenario and ask whether you should test, treat, or both.
Use the Modified Centor Criteria to guide your decision-making:
- Tonsillar exudates or asymmetry
- Tender anterior cervical adenopathy
- History of fever
- Absence of cough
Clinical Pearl: Never treat strep throat empirically based on symptoms alone; always confirm with a rapid antigen detection test (RADT) or throat culture. The gold standard treatment is Penicillin V potassium or a single intramuscular dose of Benzathine penicillin G. If your patient has a non-anaphylactic penicillin allergy, cephalexin is a great alternative. Treating strep effectively is not just about relieving symptoms today—it is about preventing acute rheumatic fever, a severe delayed complication.
3. Pertussis: The Cough That Persists
Often called the "100-day cough," pertussis is caused by the gram-negative bacterium Bordetella pertussis. It progresses through three distinct stages: catarrhal (mild cold-like symptoms), paroxysmal (severe coughing fits followed by an inspiratory "whoop"), and convalescent.
When boards test pertussis, they are usually looking to see if you can identify the paroxysmal stage and know the treatment window. Antibiotics do not drastically shorten the course of illness once the paroxysmal stage is well underway, but they are critical for eradicating the bacteria and stopping transmission to vulnerable populations like infants.
Clinical Pearl: The treatment of choice is a macrolide, such as azithromycin, clarithromycin, or erythromycin. Remember that close contacts of a confirmed pertussis case require post-exposure prophylaxis with a macrolide regardless of their vaccination status.
4. Community-Acquired Pneumonia: Outpatient Empiric Management
Community-acquired pneumonia (CAP) is a staple of primary care and board exams alike. When evaluating a patient with a productive cough, fever, pleuritic chest pain, and focal crackles on lung auscultation, a chest X-ray showing lobar consolidation confirms the diagnosis.
The key to passing board questions on CAP is knowing how to select empiric antibiotic therapy for a previously healthy adult with no recent antibiotic use:
- First-line choice: Amoxicillin high dose, doxycycline, or a macrolide (only if local pneumococcal resistance is less than 25%).
- If comorbidities are present (chronic heart, lung, liver, or renal disease, diabetes, or immunosuppression): Use a respiratory fluoroquinolone (e.g., levofloxacin) or combination therapy with a beta-lactam plus a macrolide or doxycycline.
Clinical Pearl: Always check for recent antibiotic exposure in the past 90 days. If your patient took an antibiotic recently, you must select a drug from a different class to avoid treatment failure due to resistant strains.
You have got what it takes to master these concepts and crush your board exam. Keep showing up for your studies every single day, trust your clinical instincts, and remember that every practice question brings you one step closer to your nurse practitioner cap. Head over to thefnpreview.com to access thousands of high-yield board review questions and take your preparation to the next level.