The FNP Review

The 4 Infectious Disease Scenarios Every FNP Student Must Master Before Boards

Infectious Disease · 3 min read · September 21, 2026

Introduction

Infectious disease questions make up a substantial portion of the AANP and ANCC family nurse practitioner certification exams. The secret to mastering this domain isn't memorizing endless lists of pathogens—it is recognizing the distinct clinical patterns, classic physical exam findings, and first-line treatments that board examiners love to test. Let us break down four high-yield infectious disease scenarios that frequently appear on the exam so you can score easy points.

1. Lyme Disease: Recognizing the Stages and Treatment

Lyme disease, caused by the spirochete Borrelia burgdorferi and transmitted by the blacklegged tick, is a board favorite. You must immediately distinguish between early localized disease and disseminated disease.

  • Early Localized: Characterized by erythema migrans (the classic "bull's-eye" rash), which appears 7 to 14 days after a tick bite. Patients may also report flu-like symptoms such as fatigue, headache, and myalgias.
  • Disseminated/Late: Neurological symptoms (like facial nerve palsy), multiple erythema migrans lesions, and migratory arthralgias or arthritis (especially in the large joints like the knee).

Board Pearl: Do not wait for serology or Western blot results to treat early localized Lyme disease. Diagnosis is clinical based on the presence of erythema migrans and a history of potential exposure in an endemic area.

First-line treatment for adults is doxycycline 100 mg BID for 10 days. If the patient is pregnant or a young child where tetracyclines are contraindicated, use amoxicillin.

2. Group A Streptococcus Pharyngitis: Centor Criteria in Action

Sore throat is a routine complaint in primary care, but board exams test your ability to differentiate viral upper respiratory infections from bacterial streptococcal pharyngitis to prevent unnecessary antibiotic use and complications like rheumatic fever.

Use the modified Centor criteria to guide your evaluation:

  • Fever over 38°C (100.4°F)
  • Tender anterior cervical adenopathy
  • Lack of a cough
  • Pharyngotonsillar exudates

If a patient scores 3 or 4, order a rapid antigen detection test (RADT) or throat culture. While a positive test confirms the diagnosis, remember that a positive RADT does not require a backup culture in adults because of its high specificity.

Board Pearl: The drug of choice for Streptococcal pharyngitis remains penicillin V potassium (or a single intramuscular dose of penicillin G benzathine). For penicillin-allergic patients, prescribe a first-generation cephalosporin (like cephalexin) if the allergy is mild, or azithromycin for severe reactions.

3. Pertussis: The Cough That Expires

Often called the "100-day cough," pertussis (Bordetella pertussis) starts with mild cold-like symptoms (catarrhal stage) before progressing to the paroxysmal stage, characterized by severe coughing fits followed by a high-pitched "whoop" and post-tussive emesis.

Board questions will often describe an adolescent or adult with a persistent cough who lives with or cares for an infant. Remember that adults lose their childhood immunity over time, making them a major reservoir for transmitting this dangerous infection to unimmunized infants.

Board Pearl: Macrolides (azithromycin, clarithromycin, or erythromycin) are the treatment of choice. They shorten the duration of shedding and reduce transmission, but they must be given during the catarrhal stage to significantly alter the clinical course of the cough itself. Post-exposure prophylaxis is indicated for all household contacts regardless of immunization status.

4. Community-Acquired Pneumonia: Empiric Outpatient Choices

When evaluating a patient with community-acquired pneumonia (CAP), board exams test your knowledge of empiric antibiotic selection for otherwise healthy adults without recent antibiotic use.

For a healthy adult with no comorbidities, first-line outpatient options include:

  • Amoxicillin (high dose)
  • Doxycycline
  • A macrolide (azithromycin) only if local macrolide resistance is less than 25%

If the patient has chronic comorbidities (such as heart, lung, liver, or renal disease, diabetes, or alcohol use disorder), you must use combination therapy or a respiratory fluoroquinolone (like levofloxacin) to cover atypical pathogens and resistant strains.

You have worked incredibly hard to reach this stage of your FNP journey. Trust your clinical intuition, lean into these high-yield patterns, and remember that every practice question brings you one step closer to your goal. Head over to the FNP Review to access our full question bank and take your board prep to the next level.