Leptospira Species


Indications for Testing

  • Fever >3 days with severe myalgia, usually after contact with animals or contaminated water/soil, or in person with recent travel history

Laboratory Testing

  • Darkfield microscopic exam of peripheral blood smear during first few days may demonstrate leptospires but with low sensitivity (~40%) and specificity (~60%)
    • May also use urine or CSF specimens
    • 1x104 leptospires/mL necessary to observe 1 cell/field
  • Antibody testing
    • Leptospira antibody testing for IgM in acute phase
      • Low sensitivity in first week of illness
      • Methods include microscopic agglutination (MAT), ELISA, IHA
        • MAT has highest specificity
      • Titer >1:200 and compatible symptoms are suggestive of human infection
    • Convalescent IgG – ≥2 weeks after IgM
      • Fourfold increase in titer when run in parallel with acute sample confirms human case
  • Molecular testing – PCR
    • Sensitive and rapid but not widely available
    • Useful only in first 7 days of illness
  • Culture – organism is fastidious and slow growing, occasionally requiring weeks to grow
    • May be isolated from blood, CSF and peritoneal dialysate within first 10 days of illness; thereafter, urine preferable
    • Gold standard, but not often used in diagnosis

Differential Diagnosis

Clinical Background

Human leptospirosis, an acute febrile illness that presents with many manifestations, is found worldwide.


  • Incidence – ~100-200 cases annually in U.S. (approximately half in Hawaii)
  • Transmission
    • Zoonotic disease caused by the spirochete Leptospira interrogans
      • Wild mammals (eg, rodents) serve as a primary natural reservoir, but domestic animals (dogs, cattle, swine, horses) serve as major sources of human infection
    • ~50% of infections occur from July to October
    • Transmission to humans – most often indirect by human contact with soil, food or water contaminated by urine from an infected animal
      • Common sources include contaminated well water, spring water, and food preparation surfaces
      • Transmission also occurs by swimming, rafting, or kayaking in water sources where livestock have been pastured
      • Certain occupational groups (agriculture, sewer, construction, veterinarians, and livestock/farm workers) are at higher risk for leptospirosis


  • Spirochete
    • Member of the family Spirochaetaceae – also includes Treponema and Borrelia

Risk Factors

  • Contact with contaminated water (kayaking and rafting)
  • Poor sanitation
  • Livestock/farm work
  • Meat processing work

Clinical Presentation

  • Infection has variable clinical course; usually presents as one of the following
    • Subclinical – only detectable by serologic means (~90% of infections)
    • Influenza-like febrile illness with fever, chills, rigor, myalgia, abdominal pain, vomiting and diarrhea; coincides with leptospiremia following an 8-12 day incubation period (septicemic phase)
    • Severe, life-threatening multi-organ failure; often follows influenza-like stage and transient reduction in severity of symptoms (immune phase)
  • Jaundice occurs infrequently in the U.S.
  • Leptospiral meningitis – occurs more frequently, accounting for 5-13% of sporadic lymphocytic meningitis cases
  • Kidneys are invariably involved – urine analysis demonstrates mild proteinuria, leukocytes, casts and variable hematuria
    • Jaundice with nephritis – Weil disease
      • May also have pulmonary dysfunction, hemorrhagic disease
      • Mortality 5-40% in severe cases


  • Treat with antimicrobials
  • Jarisch-Herxheimer reaction (fever, myalgias, headache, tachycardia, hypotension) may occur with initiation of treatment for all spirochetal diseases

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
Leptospira Antibody, IgM by Dot Blot 0055233
Method: Qualitative Immunoblot
Detect the presence of serum IgM to Leptospira biflexa, serovar Patoc 1, which is genetically similar to disease-causing members of the genus Leptospira

Not sensitive in first week of illness

May require convalescent IgG to confirm human infection

Leptospira Antibody 0050786
Method: Semi-Quantitative Indirect Hemagglutination

Detect Leptospira-specific IgG and IgM in serum or plasma samples in which Leptospira infection is suspected

Cannot be used to predict the point of IgM appearance or cessation in patients, nor can it be used to distinguish a current or recent leptospirosis infection from a past infection or reinfection with another serotype

Less sensitive than IgM by Dot Blot

Leptospira Culture 0060158
Method: Culture

Gold standard for Leptospira identification

Time-sensitive test

Recommend obtaining acute serology testing concurrently because test takes up to 6 weeks for evaluation

CSF should be collected within first week of illness; after first week of illness, urine should be collected