Leptospirosis Prophylaxis
Doxycycline 200 mg orally as a single dose after high-risk flood water exposure is the recommended prophylaxis for leptospirosis, while weekly doxycycline prophylaxis should be reserved only for settings with documented attack rates exceeding 10 cases per 100 person-years. 1
Primary Prevention Strategies
The first line of defense against leptospirosis is avoiding exposure rather than relying on chemoprophylaxis:
- Avoid contact with contaminated water, especially during floods, particularly if you have cuts or abrasions 1
- Use protective equipment such as boots and gloves during high-risk agricultural or occupational activities 1
- Implement rodent control measures in endemic areas as an alternative to prophylaxis 1
When to Use Doxycycline Prophylaxis
Post-Exposure Prophylaxis (Preferred Approach)
For flood victims with unavoidable water exposure:
- Single dose of 200 mg doxycycline orally provides 76.8% protective efficacy against leptospiral infection and 86.3% efficacy against clinical leptospirosis 1
- Efficacy increases significantly for those with laceration wounds 1
- This regimen can be implemented in mass prophylaxis campaigns following severe flooding with documented high attack rates 1
A pilot study in São Paulo demonstrated a protective association (RR = 2.3) for confirmed cases with single-dose doxycycline after high-risk exposure, though the sample size was limited 2. More robust evidence from a Cochrane review showed doxycycline reduced symptomatic verified leptospirosis from 4.9% to 0.6% (NNT = 24) 3.
Pre-Exposure Prophylaxis (Limited Indications)
Weekly doxycycline 200 mg should only be used when:
- Attack rates exceed 10 cases per 100 person-years 1
- Military training exercises occur in highly endemic areas with documented attack rates 1
- Short-term occupational exposures involve unavoidable prolonged water contact 1
Important caveat: A 2018 outbreak among US Marines in Okinawa demonstrated that weekly doxycycline prophylaxis failed to prevent disease (attack rate 33.9%), with no statistical difference between those who took pre- or post-exposure doxycycline 4. This challenges the traditional weekly prophylaxis approach and suggests it may not be effective in all high-exposure scenarios.
The classic 1984 Panama study showed 95% efficacy with weekly doxycycline (attack rate 0.2% vs 4.2% with placebo) 5, but more recent meta-analysis data show weekly 200 mg doxycycline does not demonstrate statistically significant benefit versus placebo (OR 0.20; 95% CI 0.02-1.87; p = 0.16) 6.
Contraindications and Special Populations
Children Under 8 Years
- Doxycycline is contraindicated in children under 8 years due to risk of permanent tooth discoloration and enamel hypoplasia 1
- Do not prescribe tetracyclines for any indication related to flood exposure in this age group 1
- For this population, focus exclusively on exposure avoidance strategies
Adverse Effects
Doxycycline prophylaxis carries a 3% adverse event rate compared to 0.2% with placebo (NNH = 39) 3. Common adverse effects are generally mild and self-limited.
Clinical Algorithm for Prophylaxis Decision-Making
Step 1: Assess exposure risk
- High-risk: Flood victims with unavoidable water contact, especially with open wounds
- Moderate-risk: Occupational exposure in endemic areas
- Low-risk: Minimal water contact, protective equipment available
Step 2: Determine prophylaxis approach
- Post-exposure (flood victims): Single dose 200 mg doxycycline orally 1
- Pre-exposure (military/occupational): Only if attack rate >10 per 100 person-years; consider weekly 200 mg doxycycline, but recognize limited efficacy data 1, 4
- All scenarios: Prioritize exposure avoidance over chemoprophylaxis 1
Step 3: Screen for contraindications
- Age <8 years: Do not use doxycycline 1
- Pregnancy: Avoid tetracyclines
- Known hypersensitivity to doxycycline