ABIM Infectious Disease common mistakes
ABIM Infectious Disease · Understand the traps and how to avoid them.
Choosing an antibiotic by matching the organism name to a remembered 'drug of choice' without first checking the local susceptibility pattern or whether the isolate is ESBL-producing, carbapenemase-producing, or otherwise resistant.
Exam stems often present a classic organism (e.g., Klebsiella, E. coli, Pseudomonas) and candidates reflexively pick the historic first-line agent, ignoring the susceptibility table embedded in the stem or the epidemiologic clues (prior carbapenem exposure, travel to a high-prevalence region).
What to do instead
Before selecting therapy, explicitly scan the stem for culture and susceptibility data, prior antibiotic exposure, recent hospitalization, and travel history; if resistance is implied, choose an agent active against the resistant phenotype (e.g., ceftazidime-avibactam or meropenem-vaborbactam for KPC, cefiderocol for metallo-beta-lactamase producers).
Treating a positive blood culture or sputum culture as automatically diagnostic of infection and starting or escalating antibiotics without assessing for contamination, colonization, or a noninfectious explanation.
Candidates conflate 'positive culture' with 'infection' and skip the pretest probability step, especially with coagulase-negative staphylococci, diphtheroids, or respiratory secretions in a patient without compatible clinical findings.
What to do instead
For each positive culture, ask whether the organism is a plausible pathogen for that site, whether multiple cultures grew it, and whether the clinical syndrome fits; when contamination is likely, repeat cultures rather than treat, and apply diagnostic stewardship principles (e.g., avoid sputum cultures in patients without pneumonia).
Missing the need to adjust antimicrobial dosing for renal or hepatic function, obesity, augmented renal clearance, or dialysis, and failing to recognize that vancomycin and aminoglycoside therapy require pharmacokinetic monitoring.
Stems bury the creatinine clearance or dialysis status in the laboratory data, and candidates focus on drug selection rather than dose optimization, or they apply standard doses to patients with severe renal impairment.
What to do instead
Calculate or estimate CrCl for every antimicrobial question and check whether the chosen agent requires dose adjustment; for vancomycin and aminoglycosides, state the monitoring plan (AUC-guided or trough monitoring, renal function checks) and consider extended-infusion beta-lactams for resistant organisms.
Failing to distinguish latent from active tuberculosis and to apply the correct interpretation of interferon-gamma release assay versus tuberculin skin test, including in BCG-vaccinated or immunocompromised patients.
Candidates memorize 'IGRA is more specific' without applying it to the specific scenario, or they treat a positive IGRA in a patient with a normal chest radiograph as active TB, or they dismiss a negative test in a patient with advanced HIV or on TNF inhibitors.
What to do instead
For each TB question, first classify as latent versus active using symptoms, chest imaging, and microbiologic data; then choose the appropriate regimen (e.g., 4R for latent TB, RIPE for active) and remember that negative IGRA/TST does not exclude active disease in immunocompromised hosts, so pursue sputum AFB smear, culture, and NAAT.
Misclassifying a fungal infection by morphology or host factor and choosing the wrong antifungal class, e.g., treating mucormycosis with voriconazole or treating invasive aspergillosis with fluconazole.
Candidates remember 'mold = voriconazole' or 'yeast = fluconazole' as blanket rules and do not link the specific host (neutropenia, diabetes with ketoacidosis, transplant) and morphology (broad nonseptate hyphae versus septate acute-angle hyphae) to the correct agent.
What to do instead
Build a two-step framework: identify host risk and morphologic pattern, then map to drug (liposomal amphotericin B plus surgical debridement for mucormycosis; voriconazole or isavuconazole for invasive aspergillosis; echinocandin first-line for candidemia). Confirm by culture or biomarker (galactomannan, beta-D-glucan) when the stem allows.
Initiating or interpreting HIV testing and antiretroviral therapy without accounting for the window period, the need for a confirmatory differentiation assay, or the risk of immune reconstitution inflammatory syndrome and drug interactions after starting ART.
Candidates treat a single reactive screening test as diagnostic, or they start ART without checking for opportunistic infections that require treatment first, or they overlook interactions (e.g., rifampin with dolutegravir, PPIs with atazanavir).
What to do instead
Follow the algorithm: fourth-generation antigen/antibody screen, then HIV-1/2 differentiation assay, with HIV RNA if acute infection is suspected; before starting ART, screen for opportunistic infections and review interactions, and anticipate IRIS in patients with low CD4 counts and high viral loads.
Missing the required post-exposure or pre-exposure prophylaxis step after a needlestick, sexual exposure, or travel-related exposure, or giving the wrong duration or agent.
Candidates focus on the exposure event and forget the protocol details (e.g., HIV PEP within 72 hours for 28 days, hepatitis B PEP depending on vaccination status, rabies PEP schedule, malaria chemoprophylaxis timing), or they omit source testing.
What to do instead
For every exposure question, list the source, the exposed person's immune status, and the time window; then apply the specific protocol (HIV PEP regimen and 28-day duration, HBIG plus vaccine for nonimmune needlestick, rabies vaccine plus immunoglobulin for category III exposures, and appropriate malaria prophylaxis by destination).
Failing to recognize when infection control precautions should change (contact, droplet, airborne) or when isolation should be discontinued, and missing the need for antimicrobial stewardship intervention such as de-escalation or discontinuation.
Candidates memorize organism-to-precation mappings but do not apply duration rules (e.g., contact precautions for MRSA or C. difficile until discharge, airborne for TB until three negative smears, droplet for influenza for 5 days) or they continue broad-spectrum therapy without a de-escalation plan.
What to do instead
For each scenario, state the transmission route and the specific precaution, then state the discontinuation criterion; for stewardship questions, identify the opportunity to narrow, stop, or switch to oral therapy based on culture data and clinical response, and document the planned duration.
Misapplying diagnostic test characteristics-treating a highly sensitive test as confirmatory, ignoring pretest probability, or ordering the wrong specimen or timing (e.g., blood cultures before antibiotics, CSF PCR versus culture, stool testing for C. difficile).
Candidates select the 'best test' by reputation rather than by the clinical question, and they forget that sensitivity and specificity translate into different predictive values depending on prevalence, or they order tests at the wrong time relative to antibiotics.
What to do instead
Before choosing a test, define the clinical question and pretest probability; obtain cultures before antibiotics whenever feasible, use NAAT for rapid pathogen detection but confirm with culture when susceptibility is needed, and avoid testing asymptomatic patients or testing without a plan to act on results.
Overlooking the immunocompromised host's specific risks-failing to provide prophylaxis (e.g., trimethoprim-sulfamethoxazole for Pneumocystis, antiviral prophylaxis after transplant), to adjust for drug interactions with immunosuppressants, or to consider atypical and opportunistic pathogens in the differential.
Candidates apply general-population differentials and standard empiric therapy to transplant, neutropenic, or biologic-treated patients, missing the need for broader coverage and prophylaxis.
What to do instead
For any immunocompromised stem, list the specific immune defect (neutropenia, T-cell deficiency, asplenia, complement deficiency), then add the corresponding prophylaxis and broaden the differential to include opportunistic pathogens; check interactions with calcineurin inhibitors and adjust antimicrobial choices accordingly.