Leptospirosis

Infectious Agent

Leptospirosis is caused by infection with Leptospira species which are helical Gram-negative aerobic bacteria. Leptospira spp. are comprised of both pathogenic and saprophytic species, the former causing disease in humans (and animals), that are further subdivided into serogroups and further still into serovars.⁽¹⁾ Pathogenic Leptospira are targeted by diagnostic confirmatory testing methods.

Case Definitions and Notification Criteria

Only confirmed cases should be notified.⁽²⁾

Confirmed case

A confirmed case requires laboratory definitive evidence only.

Laboratory definitive evidence

Isolation of pathogenic Leptospira species

OR

Detection of pathogenic Leptospira species DNA from a clinical specimen by nucleic acid testing (NAT)

OR

A fourfold or greater rise in Leptospira agglutination titre by Microscopic Agglutination Test (MAT) between acute and convalescent phase sera obtained ideally at least two weeks apart

OR

A single Leptospira agglutination titre (by MAT) greater than or equal to 400.

Laboratory suggestive criteria*

Detection of IgM antibodies against Leptospira by serology (e.g. Immunoglobulin M (IgM) enzyme-immunoassay (EIA)

*While the Public Health Laboratory Network (PHLN) (Leptospirosis – Laboratory case definition | Australian Centre for Disease Control) includes suggestive criteria in their laboratory case definition, it is not part of the CDNA surveillance case definition, nor is it notifiable. Positive IgM results are notifiable to the Notifiable Conditions System (NoCS); however, it is at the Public Health Unit’s discretion to follow-up according to capacity and local policy.

Outbreak criteria

Two or more epidemiologically linked (in time and place) cases with a local source of exposure e.g. community or workplace.

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Notification Procedure

Pathology Laboratories

To notify on pathological confirmation, by usual means.

Lab Aspects

Appropriate specimen collection for suspected leptospirosis cases should be informed by the timeline below, and should include:

• If presenting less than 10 days from symptoms onset:
  • A blood specimen for NAT (serum preferred)
  • Blood for culture⁽¹⁾
• If presenting more than 7 days since symptom onset:
  • Serum for EIA IgM and acute MAT

ALL suspected leptospirosis cases are recommended to also have:

• Convalescent MAT⁽²⁾ (ideally taken 14 to 28 days after the acute MAT or NAT)

^{(1) Culture is a complementary definitive test for the acute phase diagnosis of Leptospirosis, however, can take up to 6 weeks. Isolation of Leptospira spp. through culture supports identification of the infecting serovar which is of particular importance for public health surveillance and outbreak detection. Contact your local microbiology/pathology laboratory for further information on culture collection options.
(2) Convalescent MAT testing supports identification of the infecting serovar which is of particular importance for public health surveillance and outbreak detection.}

Specimen collection for leptospirosis cases

Collection Notes:

A combination of blood culture and NAT is recommended for acute (Leptospiraemic) phase diagnosis.

*Blood Culture: Uncoagulated whole blood. Heparin (green top tube) and EDTA (purple top tube) suitable. Where possible add 2 and 5 drops of whole blood directly into EMJH semi solid media for referral. EMJH is specialised media supplied by the QLD Leptospirosis Reference Laboratory upon request. Refer to QIS: 26605 for Guidelines for the Culture of Blood for Leptospira.

Objects of surveillance

To monitor the epidemiology of leptospirosis in Queensland and inform public health initiatives.

Public Health Significance and Occurrence

Leptospirosis occurs worldwide (except the polar regions), but is most common in tropical and subtropical areas, like Queensland.^(3,4)

Leptospirosis is predominantly a disease reported in males, linked to occupation.  Occupations reported as high risk include those in agriculture, such as the banana industry, meatworkers and dairy farmers.^(4,5) The disease is also a recreational hazard for bathers, campers and sports people exposed to contaminated waters.^(3,6) There have been several cases reported among white water rafters in Far North Queensland.⁽⁷⁾ Outbreaks can occur among those exposed to river, stream, canal and lake water contaminated by the urine and tissues of infected domestic and wild animals. Clusters have been associated with domestic and workplace rodent infestations.⁽⁸⁾

High rainfall and flooding likely contribute to the survival, growth and environmental contamination of Leptospira in water and soil, and is a major risk factor for transmission.^(4,9,10) Leptospirosis appears to be increasing globally due to the combined effects of climate change ⁽¹¹⁾, flooding, urban population growth and agricultural intensification.^(3,12)

Notifications of leptospirosis in Queensland

During the period 2021 to 2025, notifications^{^} of leptospirosis in Queensland ranged from 76 to 151, annually. Approximately 40 percent of these cases occurred in Cairns and Hinterland Hospital and Health Service.⁽¹³⁾

In 2024-2025, the notification rate was fivefold greater in males than in females and twofold greater in Aboriginal and Torres Strait Islander Queenslanders.

Notifications of leptospirosis in Queensland: 2021-2025^{^}

* Number of notifications especially in most recent periods are subject to change due to the dynamic nature of the surveillance system. For up-to-date weekly and annual notification data, see Notifiable conditions reports | Queensland Health.
# Notification rates were calculated based on Estimated Resident Population.
^ Both confirmed and probable cases were reported during this period. On 1 January 2026, the CDNA surveillance case definition changed with only confirmed cases being notifiable.

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Clinical Features

Leptospirosis is a zoonotic bacterial disease with varying manifestations. It is usually self-limiting and often clinically unapparent. Clinical illness lasts from a few days to three weeks or longer. Generally, there are 2 phases in the illness: (i) the leptospiraemic or acute phase during the first 7–14 days of illness, followed by (ii) the convalescent or immune phase. Recovery in untreated cases can take several months.

The early phase of the illness is characterised by fever with sudden onset, headache, chills, and severe myalgia (calves and thighs). Other symptoms may include nausea, vomiting, abdominal pain, diarrhoea, cough, photophobia, and rash. Conjunctival suffusion occurs in about 30% of cases.^(3,14)

Weil’s disease is often used to describe severe leptospirosis illness, although Weil’s disease more accurately refers to a syndrome of jaundice, renal impairment, and haemorrhagic manifestations such as pulmonary haemorrhage. Between 5 to 10% of clinical cases progress to severe late-phase manifestations with up to 50% of these requiring ICU admission.⁽¹⁵⁾ These include:

• prolonged fever
• jaundice
• renal failure
• bleeding
• shortness of breath (with or without haemoptysis)
• hypotension
• myocarditis
• aseptic meningitis
• confusion
• depression.⁽³⁾

The case fatality rate of severe leptospirosis is estimated to be between 5–50% and is associated with older age and multiple comorbidities. Acute respiratory distress syndrome, pulmonary haemorrhage, renal impairment and hypotension are manifestations associated with poor outcomes.^(3,16)

Cases are often under-recognised or misdiagnosed as dengue, malaria or influenza.⁽³⁾

Reservoir

Pathogenic Leptospira colonise the renal tubules of wild and domestic animals and can survive in the environment for weeks.⁽¹²⁾ Infected animals may excrete leptospires intermittently or persistently for months, years, or over their lifetime.⁽³⁾ Leptospira have been isolated from virtually all mammalian species. Cattle, pigs, and dogs serve as major reservoir hosts.

Serovars generally vary depending on the animal they infect. Rats are a common source for several serovars, including Arborea, Zanoni and Australis. Refer to appendix A for further information on serovars and animal hosts.

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Mode of Transmission

Leptospirosis is transmitted by direct contact with the urine or tissues of infected animals. Humans may also contract the infection through exposure to water, soil or environments contaminated with infected urine. This can occur during activities such as swimming, wading or white-water rafting in rivers, lakes and dams or by ingesting contaminated water. The bacteria enter through cuts in the skin, through mucous membranes, or by inhalation of aerosols from contaminated fluids.

While human-to-human transmission can occur vertically, and is theoretically possible through sexual contact or breastfeeding, reported cases are extremely rare.⁽¹⁷⁾

Incubation Period

Usually 5-14 days, with a range of 2-30 days.⁽³⁾

Period of Communicability

Leptospires may be excreted in the urine, usually for one month, although prolonged excretion has been observed in humans and in animals for months, even years, after recovering from the illness.⁽⁴⁾

Susceptibility

Following infection, immunity is likely for the specific serovar if antibody titres are sufficient, but may not protect against infection with another serovar.⁽³⁾

Vaccines for human disease are currently unavailable in Australia as they provide only short term immunity and limited protection against the most common serovars.^(18,19) Some vaccines may be appropriate for animals, depending on the serovar.

Management

Cases

Investigation

Public Health follow-up is recommended for all cases within 5 working days of notification.

See Laboratory Aspects section above for advice on specimen collection and timing.

The principles of investigation are:

1. Confirm the diagnosis. When diagnosis is not yet confirmed, recommend additional testing if still appropriate (see testing timeline in figure above). Note: some cases that are clinically diagnosed and treated may not meet surveillance case definitions in the absence of convalescent testing.
2. Identify likely source of infection. For confirmed cases, and in consultation with the treating medical practitioner, attempt to identify the source of infection such as exposure to urine or tissues of infected animals or contaminated water sources. Where appropriate, identify and follow up any co-exposed individuals.
3. Identify the serovar. If necessary, an appropriately timed MAT is recommended to identify the serovar and support serovar surveillance.
4. Refer for further investigation (if appropriate). If occupational exposure is suspected, obtain patient consent to notify WorkSafe Queensland. Notifications to WorkSafe Queensland can be made by calling 1300 362 128.

Restriction

Nil; use standard precautions in healthcare settings.

Counselling

The case should be advised of the nature of the infection and its mode of transmission.

Treatment

Treatment is the responsibility of the treating clinician. Treatment is most effective when given early in the illness and according to recommendations in the current edition of Therapeutic Guidelines. Doxycycline is the preferred antibiotic for empirical therapy because it also treats rickettsial infections that present similarly to leptospirosis.

Contact Tracing

Contact tracing is not routinely required for sporadic cases but may be indicated for recreational events and shared exposures to inform others of potential risk. Examples include rafting, swimming or fishing in freshwater creeks, rivers or other water sources where a case was likely exposed, or a shared exposure in a workplace.

Management

Advise co-exposed to seek medical advice and testing if symptoms develop.

Prophylaxis

Nil for contacts of sporadic cases.

Counselling

Contacts should be advised of the nature of the infection and its mode of transmission, and to seek medical advice early if symptoms develop.

Outbreaks

Investigation should include identifying a common source of exposure. Consideration for both potential community and occupational exposures is necessary and where workplace exposures are identified, notify WorkSafe Queensland with the case’s consent.

Consider appropriate preventative measures to minimise infection risk and environmental contamination (see below).

Community outbreaks of leptospirosis in Queensland have historically been associated with extreme weather events, such as floods and cyclones. The public health response focuses on raising awareness among health care providers (e.g. clinician alerts for GPs and EDs), delivering public health messaging to minimise exposure risks - such as promoting appropriate clothing and footwear during disaster response and recovery. Surveillance is also conducted to detect cases and identify outbreaks.

Chemoprophylaxis with medications such as doxycycline may be considered in clusters in specific occupational settings. There is very limited evidence supporting antibiotic chemoprophylaxis for leptospirosis ⁽¹⁶⁾ and the logistical challenge of providing medication to large numbers of people during disasters renders community chemoprophylaxis unfeasible in most instances.^(9,20–22)

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Preventive Measures

Prevention measures should be targeted at reducing exposure to infected animals and contaminated environments. Relevant measures for individuals, animals and the broader community include:

Individual

• Promote public awareness of possible transmission risk when undertaking recreational water-based activities including wading, swimming, and white-water rafting in potentially contaminated waters, especially after heavy rainfall and flooding.
• Recommend staff who work with animals and those at risk of exposure from contaminated water, mud or soil, to wear appropriate protective equipment (e.g. boots, gloves, protective eyewear) and cover wounds or cuts with waterproof dressings.
• Encourage frequent hand washing, especially prior to ‘hand-to-mouth’ activities (e.g. eating and smoking), or after handling animals.

Priority groups

• Target risk communication to priority groups, for example, casual labourers working on farms or overseas born people working through labour mobility schemes. These groups may be unaware of risk factors for leptospirosis and could benefit from language specific communication.

Workplaces

• Workplaces at risk of leptospirosis exposure (e.g. banana farms) should ensure provision of appropriate protective equipment and education (language specific) to all staff.
• Public Health Units should liaise with WorkSafe Australia.^(23,24)

Community, public health and environment health

• Clean and disinfect surfaces and equipment that may have been contaminated by flood waters or infected animal urine or tissues (leptospires are rapidly killed by disinfectants and desiccation).
• Alert the public in risk areas and distribute clinician alerts during periods of flooding.
• Ensure sanitation and infrastructure is maintained and repaired as soon as possible.
• Where possible, responsible parties should minimise flooding risks and respond to identified contaminated water bodies appropriately (e.g. by draining or restricting access).

Animals

• Control rodents in homes and recreational areas. Rodent infestations can be reduced with regular rubbish removal and adequate sanitation.
• Segregate infected domestic animals from others to reduce transmission risk.
• Vaccination of dogs and cattle against leptospirosis may be considered in situations where there is an elevated risk profile and where vaccination is likely to be effective.^(25–28)

References

1. Queensland Health. What is leptospirosis - Coronial and Public Health Sciences [Internet]. 2025 [cited 2026 Jun 5]. Available from: https://www.health.qld.gov.au/public-health/forensic-and-scientific-services/testing-analysis/disease-investigation-and-analysis/leptospirosis-reference-laboratory/what-is-leptospirosis
2. Australian Centre for Disease Control. Leptospirosis – Surveillance case definition [text] [Internet]. Australian Centre for Disease Control; 2026 [cited 2026 Jun 5]. Available from: https://www.cdc.gov.au/resources/publications/surveillance-case-definition-leptospirosis
3. Lau C, Craig S, Staples M, Prior S, McKay D. Leptospirosis - Control of Communicable Diseases Manual. In: Control of Communicable Disease Manual [Internet]. [cited 2026 Jun 5]. Available from: https://ccdm.aphapublications.org/doi/full/10.2105/CCDM.2745.090
4. Lau CL, Skelly C, Dohnt M, Smythe LD. The emergence of Leptospira borgpetersenii serovar Arborea in Queensland, Australia, 2001 to 2013. BMC Infect Dis. 2015 Jun 14;15:230. doi:10.1186/s12879-015-0982-0 PubMed PMID: 26072306; PubMed Central PMCID: PMC4465322.
5. Taunton C, Hayek CE, Field E, Rubenach S, Esmonde J, Smith S, et al. Undetected serovars: leptospirosis cases in the Cairns region during the 2021 wet season. Commun Dis Intell (2018). 2022 Nov 17;46. doi:10.33321/cdi.2022.46.70
6. Cunningham S, Marquardt T, Moodley N. Leptospirosis Cluster Following Recreational 4-Wheel Driving and Vehicle Recovery Exposure. International Journal of Infectious Diseases. 2022 Mar 1;Abstracts from the Eighth International Meeting on Emerging Diseases and Surveillance, IMED 2021116:S72–3. doi:10.1016/j.ijid.2021.12.171
7. Smythe L, Dohnt M, Symonds M, Barnett L, Moore M, Brookes D, et al. Review of leptospirosis notifications in Queensland and Australia: January 1998 – June 1999. Commun Dis Intell. 2000;24(6):153–7. doi:10.33321/cdi.2000.24.23
8. Katelaris AL, Glasgow K, Lawrence K, Corben P, Zheng A, Sumithra S, et al. Investigation and response to an outbreak of leptospirosis among raspberry workers in Australia, 2018. Zoonoses Public Health. 2020 Feb;67(1):35–43. doi:10.1111/zph.12652 PubMed PMID: 31550083.
9. Smith JKG, Young MM, Wilson KL, Craig SB. Leptospirosis following a major flood in Central Queensland, Australia. Epidemiol Infect. 2013 Mar;141(3):585–90. doi:10.1017/S0950268812001021 PubMed PMID: 22625176; PubMed Central PMCID: PMC9151845.
10. Wright H, Goot K, Rogers B. Spirochaetes and sunshine: leptospirosis in the aftermath of the Queensland floods - Wright - 2012 - Medical Journal of Australia - Wiley Online Library. Medical Journal of Australia. 2012; 196:500–2.
11. Epps J, Massey PD, Ranmuthugala G, Colvin A, Usher K, Heal C, et al. A One Health approach to leptospirosis: Current serosurveillance practices and climate change leave Australia at increasing risk. Australian and New Zealand Journal of Public Health. 2026 Feb 1;50(1):100297. doi:10.1016/j.anzjph.2025.100297
12. Lau CL, Townell N, Stephenson E, van den Berg D, Craig SB. Leptospirosis: An important zoonosis acquired through work, play and travel. Aust J Gen Pract. 2018 Mar;47(3):105–10. doi:10.31128/AFP-07-17-4286 PubMed PMID: 29621837.
13. Queensland Health. Queensland Health [Text] [Internet]. corporateName=The State of Queensland; jurisdiction=Queensland; 2023 [cited 2026 Jun 5]. Notifiable conditions reports. Available from: https://www.health.qld.gov.au/clinical-practice/guidelines-procedures/diseases-infection/surveillance/reports/notifiable
14. Rajapakse S. Leptospirosis: clinical aspects. Clin Med (Lond). 2022 Jan;22(1):14–7. doi:10.7861/clinmed.2021-0784 PubMed PMID: 35078790; PubMed Central PMCID: PMC8813018.
15. Stratton H, Rosengren P, Kinneally T, Prideaux L, Smith S, Hanson J. Presentation and Clinical Course of Leptospirosis in a Referral Hospital in Far North Queensland, Tropical Australia. Pathogens. 2025 Jun 28;14(7):643. doi:10.3390/pathogens14070643 PubMed PMID: 40732691; PubMed Central PMCID: PMC12300820.
16. Smith S, Liu YH, Carter A, Kennedy BJ, Dermedgoglou A, Poulgrain SS, et al. Severe leptospirosis in tropical Australia: Optimising intensive care unit management to reduce mortality. PLoS Negl Trop Dis. 2019 Dec;13(12). doi:10.1371/journal.pntd.0007929 PubMed PMID: 31790405; PubMed Central PMCID: PMC6907868.
17. Stolberg K, Richter M, Windahl U, Pyskun O, Lindahl J. Human-to-human transmission of leptospirosis: A global systematic review | medRxiv [Internet]. 2025 Sep. doi:10.1101/2025.09.02.25334635
18. Teixeira AF, Fernandes LGV, Cavenague MF, Takahashi MB, Santos JC, Passalia FJ, et al. Adjuvanted leptospiral vaccines: Challenges and future development of new leptospirosis vaccines. Vaccine. 2019 Jul 9;37(30):3961–73. doi:10.1016/j.vaccine.2019.05.087
19. Day N. UpToDate [Internet]. 2025 [cited 2026 Jun 5]. Leptospirosis: Treatment and prevention - UpToDate. Available from: https://www.uptodate.com/contents/leptospirosis-treatment-and-prevention/print
20. Win TZ, Perinpanathan T, Mukadi P, Smith C, Edwards T, Han SM, et al. Antibiotic prophylaxis for leptospirosis. Cochrane Database Syst Rev. 2024 Mar 14;3(3):CD014959. doi:10.1002/14651858.CD014959.pub2 PubMed PMID: 38483067; PubMed Central PMCID: PMC10938880.
21. Schneider MC, Velasco-Hernandez J, Min K duk, Leonel DG, Baca-Carrasco D, Gompper ME, et al. The Use of Chemoprophylaxis after Floods to Reduce the Occurrence and Impact of Leptospirosis Outbreaks. Int J Environ Res Public Health. 2017 Jun;14(6):594. doi:10.3390/ijerph14060594 PubMed PMID: 28587195; PubMed Central PMCID: PMC5486280.
22. Petersen K, Maranich A. Antibiotic Chemoprophylaxis for Leptospirosis: Previous Shortcomings and Future Needs. Trop Med Infect Dis [Internet]. [cited 2026 Jun 5];9(7). Available from: https://www.mdpi.com/2414-6366/9/7/148
23. WorkSafe Queensland. Leptospirosis cases on the rise on banana farms [Internet]. [cited 2026 Jun 5]. Available from: https://www.worksafe.qld.gov.au/news-and-events/newsletters/esafe-newsletters/esafe-editions/esafe-rural/may-2024/leptospirosis-cases-on-the-rise-on-banana-farms
24. SafeWork NSW. SafeWork NSW [Web page] [Internet]. SafeWork NSW; 2019 [cited 2026 Jun 5]. Leptospirosis. Located at: New South Wales, Australia. Available from: https://www.safework.nsw.gov.au/hazards-a-z/biological-hazards-and-diseases/leptospirosis
25. Brown DR, Peiris R, Waller C, Stedman EM, Fitzpatrick SE, Krause VL, et al. An outbreak of leptospirosis associated with cattle workers during the wet season, in the Northern Territory of Australia, 2021. Commun Dis Intell (2018). 2022 Apr 26;46. doi:10.33321/cdi.2022.46.23
26. Orr B, Westman ME, Malik R, Purdie A, Craig SB, Norris JM. Leptospirosis is an emerging infectious disease of pig-hunting dogs and humans in North Queensland. PLOS Neglected Tropical Diseases. 2022 Jan 18;16(1):e0010100. doi:10.1371/journal.pntd.0010100
27. Meat & Livestock Australia. Leptospirosis [Internet]. 2026 [cited 2026 Jun 5]. Available from: https://www.mla.com.au/research-and-development/animal-health-welfare-and-biosecurity/diseases/reproductive/leptospirosis
28. Queensland Government. Business Queensland [Internet]. [cited 2026 Jun 5]. Leptospirosis. Available from: https://www.business.qld.gov.au/industries/farms-fishing-forestry/agriculture/biosecurity/animals/diseases/guide/leptospirosis

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Appendix A: Microscopic Agglutination Test (MAT) serovar panel and commonly recognised animal hosts