What is the appropriate treatment for a patient with acute tularemia infection indicated by a positive IgM and negative IgG serology?

Acute tularemia (IgM+, IgG–): What to do now

• Treat immediately with a 10‑day course of a bactericidal agent: ciprofloxacin 750 mg orally every 12 hours (or 400 mg IV every 8 hours) for stable, non‑severe disease; use gentamicin 6 mg/kg IV/IM every 24 hours for 10 days if severe. 1

How I’m deciding (prioritizing morbidity, mortality, and QOL)

• Most recent, highest‑quality guidance (CDC 2025) recommends fluoroquinolone (ciprofloxacin or levofloxacin) or aminoglycoside (gentamicin) for all forms; choose aminoglycoside first for severe illness due to strongest historical efficacy and experience, but oral ciprofloxacin is preferred for mild‑to‑moderate cases to speed access and adherence, improving outcomes and QOL. Delays >2 weeks increase failure and complications; bactericidal agents outperform doxycycline in delayed or severe disease 1.
• Doxycycline is alternative (14–21 days) but has higher relapse/failure versus bactericidals, so not first choice when aiming to minimize morbidity and retreatment 1.

Stepwise algorithm

1. Confirm “acute” phase: IgM positive with compatible illness (fever, ulceroglandular/oropharyngeal/pneumonic/typhoidal features) supports recent infection; do not wait for IgG seroconversion. Start therapy now to reduce complications and mortality 1.
2. Severity triage:
   • Non‑severe (hemodynamically stable, no organ dysfunction/respiratory support needs): Ciprofloxacin 750 mg PO q12h (or 400 mg IV q8h) for 10 days. Levofloxacin 750 mg PO/IV daily is an acceptable alternative for 10 days 1.
   • Severe (shock, organ dysfunction, need for respiratory support, meningitis concern): Gentamicin 6 mg/kg IV/IM q24h for 10 days; consider adding ciprofloxacin if broad empiric coverage is needed. Transition to oral fluoroquinolone once defervesced and improved. Monitor levels/renal function early in therapy 1.
3. Special situations:
   • Pregnancy: Same first‑line classes per CDC 2025 (ciprofloxacin, levofloxacin, or gentamicin). For severe disease, start an aminoglycoside if possible. Avoid doxycycline monotherapy in severe disease or when treatment delays >2 weeks have occurred 1.
   • If treatment was delayed >2 weeks, prefer bactericidal therapy (ciprofloxacin or gentamicin) and consider combination therapy; expect higher risk of nodal necrosis/abscess and need for procedures 1.
4. Duration and switch:
   • Treat 10 days with fluoroquinolone or aminoglycoside; doxycycline requires 14–21 days if used. Switch IV/IM to oral once afebrile and clinically improved; switching classes is permissible if needed 1.
5. Source control and follow‑up:
   • Assess for suppurative lymph nodes; arrange aspiration/drainage when indicated to prevent rupture and speed recovery, improving QOL. Persistent fever or abscess warrants extended therapy or class change per response 1.
6. Avoid pitfalls:
   • Do not delay therapy awaiting IgG rise; do not use doxycycline alone for severe or delayed presentations due to higher relapse; monitor for aminoglycoside nephro/ototoxicity; separate fluoroquinolones from calcium/antacids to avoid absorption failure 1.

Evidence nuances

• CDC 2025 MMWR provides the most current, comprehensive guidance and dosing (highest priority) 1.
• Aminoglycosides remain preferred in severe illness; fluoroquinolones are effective and practical for milder disease. Doxycycline carries higher relapse risk; choose only when others contraindicated or as step‑down with caution 1.