Leptospirosis

March

• Case definition – reformatted to include new subsections and align with the new structure.
• Laboratory testing guidelines section – new section including removal of antigen testing.

For an overview of all updates made to the Communicable Disease Control Manual, refer to Updates to the Communicable Disease Control Manual – Health New Zealand | Te Whatu Ora .

The annual number of leptospirosis notifications fell dramatically between 1980 and 2000 and has fluctuated since.

Sources of infection can include contact with animals or with soil and water contaminated by animals. Leptospirosis is endemic worldwide with higher incidence in tropical countries. Travellers participating in recreational water activities such as rafting or kayaking are at higher risk of the disease, especially after heavy rainfall, which facilitates the spread of organisms.

Most cases in New Zealand have worked in the meat-processing industry or have had recent farm contact. Human leptospirosis is less likely to be seen where animals have been vaccinated.

Isolates seen in New Zealand include Leptospira borgpetersenii serovar hardjo, L. interrogans serovar Pomona, and L. tarassovi. The two most common serovars seen worldwide, canicola and icterohaemorrhagiae, are not considered endemic in New Zealand.

More detailed epidemiological information is available on the New Zealand institute for Public Health and Forensic Science Limited (PHF Science) surveillance website (external link).

Leptospirosis can infect all farm animals —cattle, pigs, goats, deer and dogs. Rats can also spread the disease. Serovars are adapted to one or more animal species such as:

• L. interrogans serovars Copenhageni and Icterohaemorrhagiae – rats
• L. interrogans serovar Hardjo and Pomona – cattle, sheep
• L. interrogans serovar Canicola – dogs.

Usually 10 days, with a range of 2–30 days.

Animals are the primary hosts and excrete leptospires in their urine. The organisms contaminate groundwater, soil and vegetation. Meat-processing staff may be exposed by direct contact with animal urine or organs of the renal tract. Leptospires enter humans through mucous membranes and skin (especially when abraded).

Person-to-person transmission is very rare.

Animals may excrete leptospires in urine for months to years. The organisms may remain viable for weeks in groundwater and moist soil.

Confirmed: A person who has a clinically compatible illness and has laboratory definitive evidence.

Probable: A person who has a clinically compatible illness and has laboratory suggestive evidence.

Under investigation: A person who has been notified to the medical officer of health, but information is not yet available to classify them further.

Not a case: A person who has been investigated and subsequently found not to meet the case definition.

An acute illness characterised by fever, chills, headache, myalgia, nausea, diarrhoea, abdominal pain, meningitis, cough and conjunctival suffusion (intense redness and swelling of the conjunctiva that occurs without discharge; a classic early sign of leptospirosis).

Manifestations of severe disease can include jaundice, renal failure, haemorrhage, pneumonitis and haemodynamic collapse. 

There are no epidemiological criteria for leptospirosis.

Laboratory definitive evidence

Requires at least one of the following.

• Detection of leptospiral nucleic acid by polymerase chain reaction testing.
• A 4-fold or higher increase in leptospiral microscopic agglutination titre between acute and convalescent sera.
• A single leptospiral microscopic agglutination titre of 400 or above.

Laboratory suggestive evidence

A single leptospiral microscopic agglutination titre of above 25 and below 400.

OR

A positive IgM screen for Leptospira.

Refer to Appendix 4: Direct laboratory notification of communicable diseases flowcharts for the direct laboratory notification process for Leptospirosis.

Testing may be carried out for the following reasons.

• To confirm or exclude a diagnosis of leptospirosis in a suspected case.
• To support public health services in their response to a leptospirosis outbreak by:
  • identifying and tracking transmission pathways
  • investigating the source of infection for individuals. 
• To identify exotic serovars that are notifiable to the Ministry for Primary Industries.

If leptospirosis is suspected, the following information should be obtained and included on the laboratory test request form.

• Symptoms including onset date and duration of symptoms.
• History of:
  • occupational or other contact with farm animals
  • recreational water activities
  • overseas travel.
• Any known links to another case or outbreak.

Serology is the primary diagnostic tool by either microscopic agglutination test (MAT) or immunoglobulin M enzyme-linked Immunosorbent assay (IgM ELISA).

Refer to Laboratory criteria and case classifications for confirmed and probable case definitions.

The diagnosis of leptospirosis is confirmed by a positive polymerase chain reaction (PCR) or a confirmatory serologic test. The diagnosis is not ruled out by a negative test result, because the sensitivity of Leptospira testing is suboptimal.

It is recommended that both PCR and serological testing should be undertaken to optimise sensitivity. MAT is the current gold standard serological test and is used to identify the probable causative serovar/serogroup. PHF Science is the national reference laboratory for MAT testing. 

Polymerase chain reaction (PCR)

PCR testing is used to detect leptospires in blood during the acute leptospiraemic phase of the disease typically before an antibody response is mounted. A positive blood PCR result indicates the disease in the acute phase.

PCR can also be used to detect leptospires in urine during the second week of illness; although leptospires can be excreted intermittently in the urine and shedding may be prolonged or intermittent.

A negative urine PCR result in the context of a compatible clinical illness cannot exclude the diagnosis of leptospirosis. In cases of high clinical suspicion, a second urine sample should be submitted if the initial specimen tested negative by PCR.

Serology

Immunoglobulin M (IgM) is detectable within the first week of illness and can persist for months. IgG seroconversion can take up to 3 weeks from the onset of symptoms. IgM is useful as a screening test but not a confirmatory test because of potential cross-reactivity with other diseases. For confirmatory testing, acute and convalescent samples need to be tested in parallel by MAT. There should be a minimum of 2 weeks between collection of acute and convalescent sera.

A 4-fold rise in MAT titre, or a single titre of 400 or greater, in a suggestive clinical setting is strong evidence of infection.

Microagglutination serology and surveillance

Microagglutination serology is a valuable tool for identifying the serovar likely responsible for infection. This information is critical for both clinical management and public health surveillance.

• Serovar-specific microscopic agglutination test should be performed on the clinical case’s serum to ensure accurate identification.
• Determining the infecting serovar can assist in tracing the source of infection, particularly in zoonotic cases and/or cases with overseas travel.
• Exotic serovars detected in animals are notifiable to the Ministry for Primary Industries (MPI) under the Biosecurity Act 1993 (external link).
• MPI can provide support in investigating potential animal sources of infection and implementing appropriate biosecurity measures.

Attending medical practitioners or laboratories must immediately notify the local medical officer of health of suspected cases. Notification should not await confirmation. 

All confirmed cases the Medical Officer of Health reasonably believes to have arisen from work should be referred to WorkSafe New Zealand, for occupational investigation. See ‘Reporting’ section for detail. 

See Appendix 5: Escalation pathways for more information

Obtain a history of occupational or other contact with farm animals, recreational water activities and travel. Ensure serovar-specific MATs are tested on the case’s serum.

Information on serovars can assist in investigating the source of infection. Exotic serovars in animals are notifiable to the Ministry for Primary Industries under the Biosecurity Act 1993. The Ministry for Primary Industries can assist with the investigation of animal sources.

Nil.

Advise the case of the nature of the infection and its mode of transmission.

A contact is any person who has experienced similar exposures to the case within the preceding 10 days.

Nil.

Advise all contacts to seek early medical attention if symptoms develop.

Check for other cases among contacts.

All confirmed cases should be referred to WorkSafe New Zealand, for occupational investigation. (Refer: ‘Notification procedure (external link)’ above).

In the case of a recreational water source, all swimming pools should comply with the New Zealand Standard for Pool Water Quality (NZS 5826:2010 (external link)) S 5.

Articles soiled with urine should be cleaned and disinfected.

Educate the public to avoid swimming or wading in potentially contaminated waters.

Ensure complete case information is entered into EpiSurv (external link). 

Medical officers of health are responsible for investigating a cluster of cases. 

If a cluster of cases occurs, notify the national protection clinical team (use Appendix 5: Escalation pathways for pathways for notification for awareness, or for escalation), and outbreak liaison staff at PHF Science, and complete the Outbreak Report Form. 

All confirmed cases the Medical Officer of Health reasonably believes to have arisen from work should be referred to WorkSafe New Zealand, for occupational investigation.  The following information must be provided under section 199 of the Health and Safety at Work Act 2015 (external link) 

• the name of the person who suffers or suffered from the notifiable disease  
• the nature of the disease 
  

The case must give their consent, which may be verbal, for any further information to be shared. A Worksafe inspector will investigate and enforce prevention and control.

• OSH and ACC. 2001. Guidelines for the Control of Occupationally Acquired Leptospirosis. Wellington: Occupational Safety and Health Service, Department of Labour.
• OSH. 2001. Leptospirosis: Facts for meat processing workers. Wellington: Occupational Safety and Health Service, Department of Labour.