Infectious Disease High-Yield: STIs, Pneumonia, UTI, and More for FNP Boards
Clinical High-Yield · 12 min read · April 28, 2026
Infectious disease is one of the most consistently tested sections on the FNP boards, and it rewards a specific kind of preparation: knowing the classic presentation, the causative organism, and the first-line antibiotic. The boards are not testing your ability to manage sepsis in the ICU. They are testing whether you can match a clinical presentation to the right treatment in a primary care setting.
Sexually Transmitted Infections: The Complete Board Review
Chlamydia: The most common bacterial STI in the United States. Often asymptomatic. When symptomatic: urethral discharge (men), cervicitis, pelvic inflammatory disease (women). Diagnosis: NAAT (nucleic acid amplification test) from urine or swab. Treatment: azithromycin 1g PO single dose OR doxycycline 100mg BID × 7 days. Treat partners. Screen all sexually active women ≤25 years annually (USPSTF recommendation).
Gonorrhea: Caused by Neisseria gonorrhoeae. Presentation: purulent urethral discharge (men), cervicitis, PID (women), pharyngitis, proctitis. Diagnosis: NAAT. Treatment: ceftriaxone 500mg IM single dose (or 1g if weight ≥150kg). Due to increasing resistance, dual therapy with azithromycin is no longer recommended by current CDC guidelines — ceftriaxone alone is now preferred. Treat partners. Co-test for chlamydia.
Syphilis: Caused by Treponema pallidum. The stages and their presentations are high-yield:
- Primary: painless chancre (single, indurated, clean-based ulcer) at the site of inoculation
- Secondary: diffuse maculopapular rash including palms and soles, condyloma lata, mucous patches, flu-like symptoms
- Latent: asymptomatic (early latent <1 year, late latent >1 year)
- Tertiary: gummas, cardiovascular syphilis (aortitis), neurosyphilis
Diagnosis: non-treponemal tests (RPR, VDRL) for screening, confirmed with treponemal tests (FTA-ABS, TP-PA). Treatment: benzathine penicillin G IM (single dose for primary/secondary, 3 weekly doses for latent/tertiary). Penicillin allergy: doxycycline for non-pregnant patients; desensitization and penicillin for pregnant patients (no alternative is proven safe in pregnancy).
Herpes Simplex Virus (HSV): HSV-1 (oral) and HSV-2 (genital) — though either can affect either site. Presentation: painful vesicles that ulcerate, dysuria, lymphadenopathy. Diagnosis: clinical; confirmed by viral culture or PCR from lesion. Treatment: acyclovir, valacyclovir, or famciclovir. Suppressive therapy reduces recurrences and transmission risk.
Trichomonas: Caused by Trichomonas vaginalis (a protozoan). Women: frothy, yellow-green vaginal discharge, strawberry cervix, vulvar pruritus. Men: often asymptomatic. Diagnosis: NAAT (most sensitive) or wet prep (motile trichomonads). Treatment: metronidazole 2g PO single dose (or 500mg BID × 7 days). Treat partners.
Board Pearl: The boards love to test the "which STI causes a painless ulcer?" question. The answer is syphilis (primary chancre). Painful genital ulcers: herpes (most common cause in the US), chancroid (Haemophilus ducreyi — rare in the US but tested). Lymphogranuloma venereum (LGV) causes a painless ulcer that heals quickly, followed by painful inguinal lymphadenopathy (buboes).
Pneumonia: CAP vs. HAP and Antibiotic Selection
Community-Acquired Pneumonia (CAP): Presentation: fever, productive cough, pleuritic chest pain, dyspnea. Exam: decreased breath sounds, dullness to percussion, egophony, tactile fremitus. CXR: lobar consolidation (typical) or diffuse bilateral infiltrates (atypical).
Typical CAP (lobar consolidation, productive cough, high fever): caused by Streptococcus pneumoniae (most common), Haemophilus influenzae, Moraxella catarrhalis. Treatment: amoxicillin-clavulanate or a respiratory fluoroquinolone (levofloxacin, moxifloxacin) for outpatient treatment with comorbidities.
Atypical CAP ("walking pneumonia," diffuse infiltrates, dry cough, gradual onset): caused by Mycoplasma pneumoniae (most common), Chlamydophila pneumoniae, Legionella. Treatment: azithromycin or doxycycline for outpatient treatment without comorbidities.
Severity assessment: The PSI (Pneumonia Severity Index) and CURB-65 score guide hospitalization decisions. CURB-65: Confusion, Urea >7 mmol/L, Respiratory rate ≥30, Blood pressure <90/60, Age ≥65. Score 0–1: outpatient. Score 2: consider hospitalization. Score ≥3: hospitalize.
Urinary Tract Infections: Uncomplicated vs. Complicated
Uncomplicated UTI (cystitis): Dysuria, frequency, urgency, suprapubic pain in a non-pregnant, non-diabetic woman without structural abnormalities. Caused by E. coli (80%), Staphylococcus saprophyticus (young women), Klebsiella. Diagnosis: urinalysis (pyuria, bacteriuria, nitrites, leukocyte esterase). Treatment: nitrofurantoin 100mg BID × 5 days (first-line), trimethoprim-sulfamethoxazole (TMP-SMX) × 3 days, or fosfomycin 3g single dose. Fluoroquinolones are not first-line for uncomplicated UTI due to resistance concerns.
Pyelonephritis: Fever, chills, flank pain, CVA tenderness, nausea/vomiting, plus UTI symptoms. Urine culture is essential. Outpatient treatment (mild-moderate): oral fluoroquinolone (ciprofloxacin or levofloxacin) × 7 days, or TMP-SMX × 14 days. Hospitalization for severe illness, inability to tolerate oral medications, or pregnancy.
Asymptomatic bacteriuria: Treat only in pregnant women and before urological procedures. Do NOT treat in non-pregnant adults, elderly patients in long-term care, or patients with indwelling catheters — this is a high-yield board point.
HIV: Screening, Staging, and Prophylaxis
Screening: The CDC recommends HIV screening for all adults aged 15–65 at least once, and more frequently for high-risk individuals. Opt-out screening is recommended in all healthcare settings.
Diagnosis: Fourth-generation HIV-1/2 antigen/antibody combination immunoassay is the recommended initial test. Positive results are confirmed with HIV-1/HIV-2 antibody differentiation immunoassay and HIV-1 NAT (viral load).
Staging: CD4 count and viral load guide staging and treatment decisions. AIDS is defined as CD4 <200 cells/μL or the presence of an AIDS-defining illness.
Opportunistic infection prophylaxis by CD4 count:
- CD4 <200: PCP prophylaxis (TMP-SMX first-line)
- CD4 <100: Toxoplasmosis prophylaxis (TMP-SMX covers both PCP and toxo)
- CD4 <50: MAC prophylaxis (azithromycin)
PrEP (Pre-Exposure Prophylaxis): Tenofovir/emtricitabine (Truvada or generic) is indicated for HIV-negative individuals at high risk. Screen for HIV before initiating and every 3 months during use.
Lyme Disease: The Three Stages
Lyme disease is caused by Borrelia burgdorferi, transmitted by the Ixodes tick. The boards test the three stages and their presentations.
Stage 1 (Early localized): Erythema migrans (EM) — the classic "bull's-eye" rash expanding from the tick bite site, present in 70–80% of cases. Flu-like symptoms. Treatment: doxycycline 100mg BID × 10–21 days (first-line for adults and children >8 years). Amoxicillin or cefuroxime for pregnant women and children <8 years.
Stage 2 (Early disseminated): Occurs days to weeks after the bite. Multiple EM lesions, cardiac involvement (AV block — Lyme carditis), neurological involvement (Bell's palsy, meningitis, radiculopathy — Lyme neuroborreliosis). Treatment: doxycycline for mild neurological disease; IV ceftriaxone for severe neurological or cardiac disease.
Stage 3 (Late disseminated): Lyme arthritis — large joint oligoarthritis, most commonly the knee. Treatment: doxycycline or amoxicillin × 28 days.
The Bottom Line
Infectious disease on the FNP boards rewards knowing the bug-drug pairings cold. Chlamydia = azithromycin or doxycycline. Gonorrhea = ceftriaxone. Syphilis = benzathine penicillin G. Atypical pneumonia = azithromycin. Uncomplicated UTI = nitrofurantoin. HIV prophylaxis by CD4 count. Lyme disease = doxycycline. Master these and infectious disease becomes one of your strongest sections.
→ Explore the FNP Board Review Book — every infectious disease topic covered with board-focused clinical pearls.