Issue 12 July 2004
General points
- Leptospirosis is the most commonly notified zoonotic disease in New Zealand
- Leptospira organisms are carried by many mammals including domestic pets, farm animals, and rodents. These are excreted and transmitted via the urine of infected animals
- The incidence of infection is highest in males in high-risk occupations, particularly meat workers, livestock farmers and forestry related occupations
- Although the evidence regarding antibiotic effectiveness is inconclusive, there is consensus that early treatment should be given for suspected leptospirosis
Background
Leptospirosis is the most commonly notified zoonotic disease in New Zealand with between80 and 180laboratory cases reported per year in the last decade. Although approximately 230serovars have been described world-wide only seven have been isolated from human cases in New Zealand.1,2
The mode of transmission to humans is via the urine of contaminated animals either directly or in the water or soil. Leptospires gain access to the circulation through penetration of abraded skin or intact mucous membranes and ultimately penetrate various tissues, resulting in a systemic illness with a wide spectrum of clinical features.1,2
Epidemiology
The incidence of leptospirosis has gradually decreased from around 20cases per100,000 in the1970s, to 6.5cases per100,000 in the early1990s, to 3.1cases per100,000 in2003.3,4 In New Zealand around90% of reported cases are via occupational acquisition.1 In2003, the majority of the 115cases reported were male (89%) with the highest age specific rates in the40-49 and 30-39year age groups.4 No leptospirosis-related deaths were reported. However, of the 84cases for which hospitalisation data was recorded, 35(42%) were admitted.4
The average annual incidence for specific occupational groups between1990–1998 has been estimated per100,000 per year as: meat workers 165cases, livestock farmers 92cases, forestry 24cases, and other occupations 1case.3
Between 1990 and2003 the distribution of causative serovar has changed with a larger proportion of infections caused by L.borgpeterseniisvtarassovi (pigs).3 There has been little change in the proportion of cases caused by L.borgpeterseniisvhardjo (cattle, sheep, deer) and L.interroganssvpomona (pigs, cattle, sheep, deer).3
Clinical Features
The course of the disease is variable and ranges from a mild subclinical illness to either a self-limited systemic illness (90%of cases) with most patients fully recovering within three months (anicteric), or a severe (icteric) potentially fatal condition accompanied by multi-organ failure.1 The incubation period is commonly 5–14days, but ranges from 2–30days.1 The clinical presentation is biphasic with the acute phase lasting about a week followed by an immune phase, characterised by leptospiruria.2 Most complications are associated with localisation of leptospires within the tissues during the immune phase and manifest in the second week of illness.2 The main organs affected are the kidneys, lungs, and liver. The predominant early clinical features are sudden onset of headache, muscle pain and tenderness, fever, rigors, nausea, conjunctival suffusion, a transient skin and mucosal rash, photophobia and other signs of meningism. Severe cases may progress to renal and respiratory failure, as well as pulmonary complications.
Case Definition
The current New Zealand case definition is ‘An illness characterised by fever, headaches, chills, myalgia, conjunctival suffusion, and less frequently meningitis, jaundice, or renal insufficiency’.5 Because the presentation of illness in anicteric cases is non-specific it is important to correlate illness with exposure. Diagnosis is usually confirmed retrospectively with the microscopic agglutination titre (MAT) test. MAT is currently the most reliable test and can detect serum antibodies against the most common serovars.1,2 Screening tests (usually Biorad), while sensitive, are only indicative of possible infection due to a high number of false positives and inability to identify the infecting serovar. 1,2
Case classification (1)
- Probable – a clinically compatible illness with a single raised titre of ≥400 in MAT.
- Confirmed – a clinically compatible illness that is laboratory confirmed by leptospira isolation, or a fourfold or greater rise in leptospiral MAT between acute and convalescent sera, or a single high MAT ≥800.
Treatment
Treatment differs depending on the severity and duration of symptoms at the time of presentation. Patients with flu like symptoms require only symptomatic treatment, whereas those presenting with more severe symptoms may require hospitalisation. Supportive treatment is critical with particular attention to fluid and electrolyte balance, pulmonary and cardiac function.2
Evidence regarding the effectiveness of antibiotic treatment is inconclusive. However, there is consensus that early antibiotic treatment in mild conditions with doxycycline or amoxicillin should be given for suspected leptospirosis and in more severe cases penicillin G.6,7 Because leptospirosis is generally selflimiting and difficult to confirm early, clinical trials are extremely difficult to perform. A Cochrane review8 evaluating antibiotic effectiveness (in terms of reduced mortality, duration of fever and hospital stay, and leptospiruria) identified three placebo controlled randomised trials (RCTs) involving 115patients.
Two RCTs investigated IV penicillin in hospitalised patients (1.5MU every 6hours for 7days started on average 9days into illness, 2MU every six hours for 5days), and oneRCT doxycycline (100mg BD for 7days, started within 48hours of illness) in anicteric patients. The authors concluded, due to the low methodological quality and small samples of the RCTs, that evidence of effectiveness is inconclusive and more well-designed RCTs are required.7 It is worth noting however, that in all three RCTs antibiotics either prevented or reduced the duration of leptospiruria.
A second Cochrane review9 of two RCTs involving 1,022patients (predominantly soldiers) has concluded that doxycycline may achieve prophylaxis in travellers to endemic areas.
Issues Relevant to ACC
Patients who have laboratory confirmed leptospirosis as a result of their employment are eligible for ACC cover.
References
- ESR. Leptospirosis in New Zealand: epidemiology and diagnosis. ESR Lab link. 2001; 8(2): 17-18.
- Levett, PN. Leptospirosis. Clinical Microbiology Review. 2001;296-326.
- Thornley CN. Human leptospirosis in New Zealand: surveillance, epidemiology and prevention, in Public Health Medicine. 2000, University of Otago: Wellington.
- ESR. Notifiable and other diseases in New Zealand. Annual Report 2003. 2004; 26-27.
- Communicable disease control manual. Wellington: Public Health Group Ministry of Health, 1998.
- Ajay R, et al. Leptospirosis: a zoonotic disease of global importance. The Lancet Infectious Diseases. 2003;3(12).
- Long SS, et al. Principles and Practice of Pediatric Infectious Diseases. 2nd ed. 2002. London: Churchill Livingstone.
- Guidugli, F et al. Antibiotics for leptospirosis. The Cochrane Library. 2004;Vol 2.
- Guidugli, F et al. Antibiotics for preventing leptospirosis. The Cochrane Library. 2004;Vol 2.