Leptospirosis

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 Institute of Environmental Science and Research (ESR) surveillance website.

An acute illness characterised by fever, chills, headache, myalgia, nausea, diarrhoea, abdominal pain, meningitis, cough and conjunctival suffusion. Manifestations of severe disease can include jaundice, renal failure, haemorrhage, pneumonitis and haemodynamic collapse.

Laboratory definitive evidence for a confirmed case requires at least one of the following:

• isolation of leptospires from a clinical specimen
• detection of leptospiral nucleic acid from a clinical specimen
• a four-fold or greater rise in leptospiral microscopic agglutination titre (MAT) between acute and convalescent sera
• single high antibody titre of ≥ 400 in the MAT.

Laboratory suggestive evidence for a probable case requires single raised agglutination titre by MAT of < 400.

It is recommended that both nucleic acid testing (NAT) and MAT testing be undertaken to improve diagnostic accuracy. MAT is the current gold standard serological test and is used to identify the probable causative serovar/serogroup. ESR-NCBID is the national reference laboratory for MAT.

Serology

IgM can be detectable within the first week of illness and can persist for months. 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.

Nucleic acid testing (for example, polymerase chain reaction – PCR)

NAT is highly sensitivity for diagnosis of leptospirosis. NAT can be used to detect leptospires in blood during the acute leptospiraemic phase of the disease typically before an antibody response is mounted. NAT can also be used to detect leptospires in urine during the second week of illness; shedding may be prolonged and intermittent.

Leptospires can be excreted intermittently in the urine. Therefore, a negative 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 NAT.

• Under investigation: A case that has been notified, but information is not yet available to classify it as probable or confirmed.
• Probable: A clinically compatible illness with laboratory suggestive evidence.
• Confirmed: A clinically compatible illness with laboratory definitive evidence.
• Not a case: A case that has been investigated and subsequently found not to meet the case definition.

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.

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. 

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’ 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) 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. 

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

If a cluster of cases occurs, contact 0800GETMOH - CD option, and outbreak liaison staff at ESR, 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 

• 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.