Leptospira Species - Leptospirosis

Human leptospirosis is an acute febrile illness that presents with many manifestations and is found worldwide. A severe form, which includes jaundice, kidney failure, and bleeding, is called Weil disease. Laboratory studies can confirm the diagnosis and determine the extent of organ involvement. Testing may include culture and/or serology.


Indications for Testing

  • Fever >3 days with severe myalgia in patients with
    • Contact with infected animals or
    • Contact with water or soil contaminated with urine of infected animal

Laboratory Testing

  • Darkfield microscopic exam of peripheral blood smear during first few days may demonstrate leptospires
    • Low sensitivity and specificity
    • May also use urine or cerebrospinal fluid (CSF) specimens
    • 1x104 leptospires/mL necessary to observe 1 cell/field
  • Antibody testing
    • IgM testing in acute phase
      • Low sensitivity in first week of illness
      • Methods include microscopic agglutination (MAT), enzyme-linked immunosorbent assay (ELISA), indirect hemagglutination antibody (IHA) – MAT has highest specificity
      • Titer >1:200 and compatible symptoms are suggestive of human infection
    • IgG testing in convalescent phase
      • ≥2 weeks after initial testing
      • 4-fold increase in titer confirms human infection
  • Molecular testing – polymerase chain reaction (PCR)
    • Sensitive and rapid but not widely available
    • First 7 days of illness only
  • Culture – gold standard, but not often used in diagnosis
    • 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
    • Urine preferable after 10 days

Differential Diagnosis



  • 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) – primary natural reservoir
      • Domestic animals (dogs, cattle, swine, horses) – major source 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 infected animals
      • 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

  • Occupational exposure – farmers, ranchers, trappers, lab workers
  • Recreational exposure – canoeing, kayaking, rafting, swimming, wading
  • Household exposure – livestock, pets, rodents
  • Other – flooding, walking barefoot through surface water

Clinical Presentation

  • Variable clinical course
    • Subclinical – only detectable by serologic means (~90% of infections)
    • Self-limiting influenza-like illness
      • Fever, chills, rigor, myalgia, abdominal pain, vomiting, and diarrhea
      • Coincides with leptospiremia following a 2-day to 4-week (CDC, 2017) incubation period
    • Severe, life-threatening multiorgan failure – often follows influenza-like stage and transient reduction in severity of symptoms (immune phase)
  • Leptospiral meningitis – accounts for 5-13% of sporadic lymphocytic meningitis cases
  • Renal involvement common
    • 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 case

ARUP Laboratory Tests

Aid in the detection of acute leptospirosis

Antibodies may not be present during early disease; confirmation 2-3 weeks later is recommended

May provide definitive diagnosis, but sensitivity is low and culture may take several weeks to yield result

Time-sensitive test


Additional Resources

Medical Experts



Marc Roger Couturier, PhD, D(ABMM)
Professor of Pathology (Clinical), University of Utah
Medical Director, Emerging Public Health Crises, Parasitology/Fecal Testing, and Infectious Disease Antigen Testing, ARUP Laboratories


Mark A. Fisher, PhD, D(ABMM)
Associate Professor of Pathology (Clinical), University of Utah
Medical Director, Bacteriology, Special Microbiology, and Antimicrobial Susceptibility Testing, ARUP Laboratories