Infectious Disease Board Prep for Family Medicine

Five-minute daily sessions on antibiotic selection, STI treatment, TB screening, and the infections that fill a family medicine schedule.

Infectious disease is everywhere on the ABFM because it is everywhere in family medicine — the blueprint distributes infection questions across respiratory, skin, genitourinary, and pediatric content rather than fencing them into one section. What unifies them is a single tested skill: choosing the right antimicrobial, at the right dose, for the right duration — and, just as often, choosing none at all. Antimicrobial stewardship is not a garnish on this category; it is the category.

The outpatient infections are the core. Community-acquired pneumonia, acute otitis media, streptococcal pharyngitis, sinusitis, cellulitis and abscess, and urinary tract infections each carry specific first-line regimens and specific traps: the amoxicillin-clavulanate indication when otitis media comes with purulent conjunctivitis, the watchful-waiting window for sinusitis, incision and drainage as the primary therapy for abscess. Shorter courses have won in study after study, and the exam has kept pace — five days is the new ten for more conditions than most older references admit.

Sexually transmitted infections are a reliable question source because the regimens change and the exam checks whether you changed with them: ceftriaxone monotherapy at higher dosing for gonorrhea, doxycycline as preferred chlamydia therapy outside pregnancy, benzathine penicillin G for syphilis at stage-dependent dosing, and expedited partner therapy where legal. HIV prevention is now core family medicine — USPSTF gives PrEP a grade A, and screening questions treat HIV and hepatitis C testing as routine.

Round out the category with latent tuberculosis (IGRA testing and the short-course rifamycin regimens that have replaced nine months of isoniazid), tick-borne disease, influenza and COVID antiviral windows, and C. difficile — where oral vancomycin or fidaxomicin replaced metronidazole as first-line years ago and the exam still finds test-takers who missed it. Where vaccination guidance appears, current questions anchor to the specific issuing body (AAFP, AAP, ACOG) given the divergence between CDC/ACIP and specialty societies since 2026.

High-yield infectious disease topics

• Community-acquired pneumonia: outpatient triage and treatment. Use clinical judgment plus a severity score (CURB-65 or PSI) for site of care. Healthy outpatients: high-dose amoxicillin or doxycycline; macrolide monotherapy only where pneumococcal macrolide resistance is under 25 percent, which is uncommon. Comorbidities: amoxicillin-clavulanate or a cephalosporin plus a macrolide, or monotherapy with a respiratory fluoroquinolone. Five days of therapy suffices with clinical stability.
• Acute otitis media and pharyngitis in the office. AOM: high-dose amoxicillin first-line; amoxicillin-clavulanate when there is concurrent purulent conjunctivitis (nontypeable H. influenzae), amoxicillin within 30 days, or treatment failure. Observation is an option for mild unilateral disease in children over two. Pharyngitis: test before treating (Centor criteria guide testing, not empiric antibiotics); penicillin or amoxicillin remains the answer — resistance does not exist for group A strep.
• Skin and soft tissue: cellulitis versus abscess. Nonpurulent cellulitis targets streptococci: cephalexin. Purulent disease or abscess raises MRSA: incision and drainage is the primary therapy for abscess, with TMP-SMX or doxycycline added for larger abscesses, surrounding cellulitis, or systemic signs. Recognize necrotizing infection red flags — pain out of proportion, rapid progression, crepitus — as a surgical emergency.
• STI treatment per current CDC regimens. Gonorrhea: ceftriaxone 500 mg IM once (1 g at 150 kg or more) — no more dual therapy with azithromycin. Chlamydia: doxycycline 100 mg twice daily for seven days preferred; azithromycin single-dose in pregnancy. Syphilis: benzathine penicillin G 2.4 million units IM once for early syphilis, weekly times three for late latent. Test of cure for pharyngeal gonorrhea; retest all patients at three months for reinfection.
• HIV screening, PrEP, and hepatitis C. Screen everyone 15 to 65 at least once (USPSTF grade A), plus risk-based repeat testing. PrEP for people at increased risk is grade A: daily tenofovir-emtricitabine or long-acting cabotegravir, with renal monitoring and quarterly HIV testing. Hepatitis C: one-time universal screening for all adults 18 and older, and treat essentially everyone with direct-acting antivirals — cure rates exceed 95 percent.
• Latent tuberculosis: testing and short-course treatment. IGRA is preferred over tuberculin skin testing in BCG-vaccinated patients and anyone unlikely to return for reading. Rule out active disease (symptoms, chest radiograph) before treating latent infection. Preferred regimens are the short courses: three months of weekly isoniazid plus rifapentine (3HP), or four months of daily rifampin (4R) — better completion, less hepatotoxicity than nine months of isoniazid.
• Tick-borne disease and Lyme prophylaxis. Erythema migrans is a clinical diagnosis — treat with doxycycline, do not wait for serology. Single-dose doxycycline prophylaxis after a bite requires an identified deer tick attached 36 hours or more, within 72 hours of removal, in an endemic area. Doxycycline is now considered acceptable in young children for short courses. Fever plus cytopenias after tick exposure suggests anaplasmosis or ehrlichiosis — treat empirically with doxycycline.
• C. difficile and antibiotic-associated diarrhea. First episode: oral fidaxomicin preferred, oral vancomycin the accepted alternative — metronidazole is no longer first-line. Stop the inciting antibiotic. First recurrence: fidaxomicin or a tapered-pulsed vancomycin course; consider bezlotoxumab for high recurrence risk; fecal microbiota therapy after multiple recurrences. Test only symptomatic patients — treating a positive test without diarrhea is a tested error.

ABFM exam tips

Look for the conjunctivitis in the otitis stem. Otitis media plus purulent conjunctivitis is the otitis-conjunctivitis syndrome — nontypeable H. influenzae, often beta-lactamase producing — and the answer jumps from amoxicillin to amoxicillin-clavulanate. Recent amoxicillin exposure triggers the same upgrade.

Shorter is the new standard. Five days for CAP with clinical stability, five to seven for cystitis-adjacent infections and cellulitis, no antibiotics at all for bronchitis and most sinusitis. When two durations appear as answer choices and the patient is improving, the shorter one usually wins.

I&D beats antibiotics for abscess. Incision and drainage is the definitive treatment; antibiotics are the adjunct, not the substitute. A stem offering antibiotics alone for a fluctuant abscess is testing whether you reach for the scalpel first.

Know the current gonorrhea and chlamydia regimens cold. Ceftriaxone 500 mg IM alone for gonorrhea; doxycycline seven days for chlamydia except in pregnancy. Answers reflecting the old dual therapy or single-dose azithromycin default are date-stamped distractors.

Choose the short-course latent TB regimens. 3HP (12 weekly doses) or 4R (four months of rifampin) beat nine months of isoniazid on completion and hepatotoxicity. But first confirm the chest radiograph is clean — treating active TB with a latent regimen is the buried catastrophe the stem is checking for.

No antibiotics is often the tested answer. Acute bronchitis, most sinusitis inside the watchful-waiting window, viral pharyngitis with a negative strep test, asymptomatic bacteriuria — the exam heavily rewards withholding. If the vignette paints a viral picture and one answer says supportive care, take it seriously.

Common pitfalls

Do not give metronidazole first-line for C. difficile. Guidelines moved to oral fidaxomicin or vancomycin years ago; metronidazole persists only where the preferred agents are unavailable in mild disease. This is among the most common stale-knowledge traps in the category.

Do not treat a positive strep screen in a patient who was not tested appropriately — or skip testing entirely. Centor criteria select who to test; they do not justify empiric antibiotics. Conversely, do not test toddlers under three routinely or chase carriers after treatment. The sequencing — criteria, then test, then penicillin — is the answer.

Do not use fluoroquinolones as first-line for uncomplicated infections. Cystitis, sinusitis, and bronchitis-adjacent stems offering ciprofloxacin or levofloxacin are testing the FDA warnings (tendinopathy, neuropathy, aortic risk) and stewardship. Reserve fluoroquinolones for pyelonephritis, complicated infections, and true allergy corners.

Do not miss the empiric-doxycycline reflex for rickettsial disease. Fever, headache, myalgias after tick exposure — with or without rash — gets doxycycline immediately in all ages; waiting for serology in suspected Rocky Mountain spotted fever is the fatal delay the question simulates.

Do not order serology for early localized Lyme. Erythema migrans in an endemic area is treated on sight; antibody testing is insensitive in the first weeks and only muddies the stem. Serology belongs to disseminated or late presentations.

Do not screen or treat pharyngeal colonization dilemmas with the wrong follow-up. Pharyngeal gonorrhea is the one site requiring a test of cure (at 7 to 14 days). Skipping it — or applying test of cure to everything — both appear as distractors.

Do not conflate influenza and COVID antiviral windows with hopeless cases. Oseltamivir works best within 48 hours but is still indicated beyond that window for hospitalized and high-risk patients; nirmatrelvir-ritonavir requires attention to interactions (statins, tacrolimus, some anticoagulants). The interaction check is frequently the actual question.

Frequently asked questions

What infectious disease topics are most tested on the ABFM?

Outpatient antibiotic selection leads: pneumonia, otitis media, pharyngitis, sinusitis, cellulitis and abscess, and UTIs, each with stewardship angles. STI regimens, HIV screening and PrEP, hepatitis C screening, latent TB testing and short-course treatment, tick-borne disease, and C. difficile management fill out the reliable core.

How much infectious disease is on the ABFM exam?

The ABFM distributes infection questions across organ-system categories rather than reporting a single ID percentage — respiratory infections count toward respiratory, STIs toward population health and genitourinary content, and so on. Summed across systems, infection management is one of the most frequently tested skills on the exam.

What changed in STI treatment that the exam tests?

The CDC moved gonorrhea to ceftriaxone monotherapy at 500 mg IM (dropping routine azithromycin co-treatment) and made doxycycline the preferred chlamydia regimen outside pregnancy. Syphilis dosing by stage, expedited partner therapy, and the three-month reinfection retest are also current emphasis areas. Older prep materials miss all of these.

IGRA or skin test for tuberculosis screening?

IGRA is preferred for anyone BCG-vaccinated (no cross-reaction) and anyone unlikely to return within 48 to 72 hours for a skin-test reading. The skin test remains acceptable, and serial testing in healthcare settings has its own rules. Either way, a positive screen requires symptom review and chest imaging to exclude active disease before latent treatment begins.

How does the exam handle vaccination questions now?

Carefully — and so should you. Since the 2026 divergence between CDC/ACIP and the major specialty societies, well-written questions attribute recommendations to a specific body (AAFP, AAP, ACOG) rather than a generic "the schedule." PulseMD questions cite the issuing organization explicitly so the answer is defensible regardless of which body a stem invokes.

When do antibiotics actually help sinusitis?

Reserve them for persistent symptoms beyond about 10 days without improvement, severe onset (high fever with purulent discharge or facial pain for 3 or more consecutive days), or worsening after initial improvement (double sickening). First-line is amoxicillin-clavulanate. Everything milder gets analgesia, intranasal steroids, and time — the watchful-waiting answer the exam rewards.

How should I study infectious disease in five-minute daily sessions?

Build drug-bug-duration triads one infection at a time — the format maps perfectly onto spaced repetition. Then layer in the stewardship judgment questions, because half the tested skill is recognizing when the answer is no antibiotic, a shorter course, or drainage instead of a prescription. Rotating a few STI and TB regimen cards keeps the fast-changing facts current.