Leptospirosis
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BACKGROUND
Reason for this study at this time
In June 2001 the "Guidelines for the Control of Occupationally Acquired Leptospirosis" were published as a joint project between the Department of Labour and the Injury Prevention Division of the Accident Compensation Corporation and the Meat Industry Association. The aim of the Guidelines was to provide practical suggestions for the management of the workplace health hazard presented by the bacteria which can cause leptospirosis in humans.
It was emphasised at that stage that the prevention of leptospirosis called for a partnership between many different parties and a combined and concerted effort. With this in mind the Accident Compensation Commission (ACC) and the Department of Labour (DOL) undertook to take the lead in a collective approach to managing a disease which it was acknowledged could be costly in terms of human health and economic output.
In the period between 2001 and 2006 there were a number of reports that indicated the incidence of leptospirosis in humans could be back on the increase after a steady decline from the 1970's and that more cases were coming from the South Island. Current data capture relies on information coming from the Institute of Environmental Science and Research (ESR) and the Notifiable Occupational Disease System (NODS) but it appeared that less than 5% of reports come through these avenues and of those at least 50% arise from a combination of the meat processing and dairy industries.
Two new features were the incidence of leptospirosis being contracted by employees in "sheep only" processing plants and indications of high rates of positive tests in some deer herds. There were perceptions supporting the notion that vaccination of sheep is not cost-effective and there had been a number of the initiatives proposing research into relevant avenues of human and animal health relating to leptospirosis. However it has proved very difficult to identify sources of funding to enable these integrated research projects to be commenced.
Scope of this study - Terms of Reference
The scope of this study was as follows:
- To undertake a review of written work since 2000 on occupationally acquired leptospirosis and of current trends in the incidence of the disease and the success of present prevention methods - with the view to providing written advice to assist in identifying one or more avenues to which the Department of Labour could direct resources in order to reduce the incidence and severity of occupationally acquired leptospirosis in New Zealand.
- Separate, brief, written advice about the feasibility of delivering a one-day workshop at which the report would be presented and discussed and, if considered feasible to deliver such a workshop, advice of whom to be invited to attend and suggestions for topics to be covered at the workshop.
The research has been carried out within a framework developed by the Department of Labour's Health Advisors Team as the preferred strategy for research projects. The report endeavours to address the key research topics that are relevant for this issue.
During discussions during the final stages of drafting the report it was emphasised that the DOL was not funded to facilitate the research in the areas identified and therefore attention should be given to how initiatives being taken by the industry stakeholders could be coordinated and extended to address these needs. Accordingly this dimension is now addressed in the report.
Additionally it was suggested that the most appropriate timing for a possible workshop was after industry stakeholders had had the opportunity to study the report and time to consider possible responses and contributions to the challenges and possibilities identified for further work.
What is Leptospirosis?
Leptospirosis is an acute generalised infectious disease characterised by extensive vasculitis, caused by Leptospira species. It is primarily a disease of wild and domestic animals, and humans are infected through direct or indirect contact with infected urine. Human to human transmission is extremely rare and has not been recorded in New Zealand. Leptospirosis is the World's most common Zoonotic Disease, New Zealand's most common occupationally acquired infectious disease and its incidence in New Zealand is high in comparison with other temperate developed countries (Thornley et al 2002).
Leptospirosis is a notifiable disease in New Zealand. Public health services obtain additional case demographic and risk factor data from the notifying doctor and this information is entered into the surveillance database (EpiSurv). The disease is also under laboratory surveillance. Specimens from cases are referred for additional serological testing using the microscopic agglutination test (MAT).
This testing is carried out at ESR and a small number of other diagnostic laboratories. These laboratory and notification data are collated nationally by ESR for the New Zealand Ministry of Health (Baker et al 2004).
Leptospira spp. have been ranked as one of the most successful of vertebrate pathogens and is nominated as the world's most widespread zoonosis (Plank and Dean 2000). Leptospires possesses an impressive array of strategies which enable it to elude control, including wide antigenic variation, the ability to infect a broad range of species, sophisticated mechanisms of host-adaption including the ability to remain in hosts for long periods and continue shedding in the urine. Additionally they the exhibit the capacity to survive for long periods in temperate and moist environments, and have multiple modes of transmission and entry into hosts (Davies 2003).
There are over 200 Leptospira serovars classified into 23 serogroups (Bolin 2004). A new and alternative scheme based on genomic considerations classifies the pathogenic organism into several species. While this has interesting implications for future research for the purpose of this report serovars are written as if they were a single species e.g. Leptospira hardjo and Leptospira pomona. As recorded by Worthington in 1982, over the years since Leptospira were first identified in New Zealand in 1951 the following species have been isolated from animals in this country Leptospira borgpetersenii sv. hardjo, Leptospira interrogans sv. pomona, Leptospira balcanica, Leptospira copehageni, Leptospira borgpetersenii ballum, and Leptospira tarrasovi. There is one report (Thompson 1980) of Leptospira australis being isolated from a human.
In humans serological diagnosis indicates that five of the species endemic in farm animals infect humans with the most common being L. hardjo, L. pomona, and L. ballum - and the other two being L.tarrasovi and L. copenhageni..
L. balcanica which is associated with possums in New Zealand has not been reported in humans. Leptospira spp other than the above are classified by the Ministry of Agriculture and Forestry as "other exotic organisms" (MAF 2004).
Many of the Leptospira spp are adapted to a particular host species (known as the maintenance host), in which an almost symbiotic relationship has been formed. Species other than the maintenance host may be more resistant to infection but if infected are more susceptible to disease. L. hardjo for example infects most cattle in an endemic situation that only causes occasional cases of disease in cattle. However it has been recorded as being responsible for the majority of cases of this disease in humans (accidental hosts). In maintenance hosts post mortem examination shows that the Leptospira may localise in the kidneys. In the farm situation the animals may continue to excrete the organism in their urine for many months, if not years.
The disease is spread in water and mud contaminated with infected urine. Flooding, or irrigating, can be a significant means of spreading infected material in the pastoral situation. Infection can occur by mouth or through the skin, particularly through abrasions and wounds. It is understood that diseased animals shed more organisms and are more important sources of infection than chronic carriers of infection. In accidental hosts the incubation period may be from 2 -16 days and is followed by a period when the bacteria are present in the blood and hence able to spread to other organs in the body.
The Ministry of Agriculture and Forestry has reported that at the 2004 general session of the World Organisation for Animal Health (OIE) members voted to remove the leptospirosis chapter from the OIE Terrestrial Animal Health Code because of the ubiquity of the organism and the absence of meaningful control programmes and effective treatments in live animals (Pharo 2005)
What does it do to people?
Clinically in humans, leptospirosis ranges in severity from a mild sub-clinical illness to either a self-limited systemic illness (some 90% of cases) with most patients fully recovering within three - four months, or a severe potentially fatal condition accompanied by multi-organ failure.
The incubation period is commonly 5 - 14 days, but ranges from 2 -30 days. The onset, and the way the condition presents clinically is often of two phases, with the first acute phase lasting about a week followed by an immune phase characterised by the shedding of leptospires in the urine. Most complications are associated with the build-up of leptospires within the tissues during the immune phase and are most likely to manifest in the second week of illness.
The main organs likely to be affected are the kidneys, lungs, and liver. The predominant early clinical features are the sudden onset of headache, muscle pain and tenderness, fever, rigors, nausea, conjunctival suffusion or redness, transient skin and mucosal rash, photophobia, and other signs in which the symptoms simulate a meningitis, but in which no actual inflammation of these membranes is present. i.e. meningism. Severe cases may progress to renal and respiratory failure, as well as pulmonary complications.
Illness caused by the serovars present in New Zealand is seldom fatal, although some deaths have been recorded. Illness caused by some serovars present in other countries can result in fatalities of between 10 and 20% of those infected.
ACC's current New Zealand case definition is:
"An illness characterised by fever, headaches, chills, myalgia, conjunctival suffusion, and less frequently meningitis, jaundice, or renal insufficiency. Because the presentation of illness in anicteric (i.e. not associated with jaundice) cases is non-specific it is important to correlate the illness with exposure."(ACC Review: Leptospirosis in New Zealand July 2004)
What have been the trends in New Zealand since 1990 and since 2001?
The annual number of cases in New Zealand peaked at 875 in 1971. The annual incidence of human leptospirosis in New Zealand declined from 5.7 per 100,000 of population in 1990-92 to 2.9 per 100,000 in 1996-98 (Thornley 2002) but over the period 2001 - 03 there was an average of 118 notifications (3.2 per 100,000) and 148 laboratory identified cases (4.0 per 100,00) per year. The incidence in this period was significantly higher than in the previous three year period reversing a long-term decline in rates of this disease in New Zealand (Baker and Lopez 2004).
It would appear that this was a short term trend as in 2004 there were 102 cases (2.7 per 100,000) and this declined further in 2005 when there were 86 cases notified (2.3 per 100,000) and this increased only slightly in 2006 when 89 cases were notified.
Of the 86 notified cases in 2005, 67 were laboratory confirmed and in addition there were a further 42 cases which were laboratory reported but not notified (ESR Annual Report 2005).
No leptospirosis related deaths were reported in 2005. Of the 80 cases for which hospitalisation status was recorded, 36 (45%) were hospitalised.
- One death has been attributed to Leptospirosis - after a fisherman handling nets was exposed to rat urine.
The trends of Leptospirosis notifications in New Zealand from 1997 - 2005 are shown in Figure 1 below.
Figure 1: Leptospirosis notifications in New Zealand 1997 - 2005
Click here for Description of Figure 1
Source: New Zealand Public Health Observatory - data reported by ESR as at 16 February 2006
Occupation was recorded for 82 (95.3%) of the 86 notified cases. Of these, 75 cases (91.4%) were recorded as engaged in occupations previously identified as high risk for exposure to Leptospirosis spp in New Zealand and the proportion in high-risk occupations has changed little over the last two years being 93.1% in 2004 and 86.3% in 2003.
Of the 82 cases in 2005 with recorded occupation, 39 (47.6%) worked in the meat processing industry (as either freezing workers, butchers, meat inspectors, meat processing managers, and meat processing cleaning supervisors) and 36 (43.9%) were farmers, farm workers, or stock truck drivers. Cases in the 2005 year also included one possum hunter, one market gardener, one contractor (engaged in stock/effluent pond cleaning), one furniture manufacturer (who also had contact with animal manure), one coalmine supervisor (who also had a hobby farm) one concrete cutter, and one plumber. (ESR Annual Report 2005).
The highest age specific rates were reported in the 40 - 49 years with 30 cases (5.6 per 100,000 population) and there were 21 cases in the 50 - 59 years (5.0 per 100,000 population). Males comprised 93.0% of the cases and ethnicity was recorded for 74 of the 86 cases. Of these rates were highest for the Maori ethnic group with 16 cases or 3.0 per 100,000 population.
On the ESR's EpiSurv database serovar data was recorded for 67 of the 86 cases in 2005 with L. hardjo 46 cases (69%), L. pomona 13 cases (19%), L. ballum 6 cases (9%), and L. tarassovi 2 cases (3%).
Table 1 shows cases by District Health Board for the period 1997-98 through June 2005. Over the whole period 1997 - 2005 the District Health Boards recording the highest percentage of cases were Waikato, Hawkes Bay, Canterbury, Northland, and MidCentral.
In the period from 2000 - 2005, compared with the total period 1997 - 2005, increases in the percentage of cases have been recorded by Waikato, Hawkes Bay, MidCentral, Bay of Plenty and Southland. Decreases in this period have been recorded by Canterbury, Northland, and Taranaki.
| DHB | 1997-98* | 1998-99 | 1999-00 | 2000-01 | 2001-02 |
|---|---|---|---|---|---|
| Auckland | 2 | ||||
| Bay of Plenty | 1 | 3 | 3 | 7 | 8 |
| Canterbury | 7 | 5 | 14 | 6 | 8 |
| Capital and Coast | 2 | 2 | 2 | ||
| Counties Manukau | 3 | 1 | 2 | 1 | |
| Hawke's Bay | 13 | 7 | 7 | 10 | 23 |
| Hutt | 1 | ||||
| Lakes | 2 | 2 | 1 | 2 | 1 |
| Mid-Central | 5 | 4 | 4 | 5 | 10 |
| Nelson/Marlborough | 4 | 4 | 5 | 5 | 6 |
| Northland | 8 | 6 | 11 | 8 | 13 |
| Otago | 1 | 1 | 4 | 2 | 3 |
| South Canterbury | 1 | 1 | 4 | 7 | 7 |
| Southland | 1 | 3 | 3 | 1 | |
| Tairawhiti | 4 | 1 | 2 | 8 | 7 |
| Taranaki | 3 | 2 | 7 | 4 | 2 |
| Waikato | 9 | 13 | 11 | 22 | 20 |
| Wairarapa | 3 | 1 | 1 | ||
| Waitemata | 2 | 3 | 2 | 8 | |
| West Coast | 1 | 2 | 4 | 1 | 2 |
| Whanganui | 1 | 2 | 2 | 1 | 1 |
| Total for year | 64 | 61 | 86 | 100 | 124 |
| DHB | 2002-03 | 2003-04 | 2004-05 | Total | % |
|---|---|---|---|---|---|
| Auckland | 1 | 1 | 4 | 0.5 | |
| Bay of Plenty | 6 | 2 | 7 | 37 | 4.9 |
| Canterbury | 9 | 12 | 4 | 65 | 8.6 |
| Capital and Coast | 2 | 8 | 1.1 | ||
| Counties Manukau | 4 | 3 | 1 | 15 | 2.0 |
| Hawke's Bay | 20 | 12 | 16 | 108 | 14.2 |
| Hutt | 1 | 0.1 | |||
| Lakes | 4 | 1 | 13 | 1.7 | |
| Mid-Central | 9 | 11 | 9 | 57 | 7.5 |
| Nelson/Marlborough | 13 | 8 | 5 | 50 | 6.6 |
| Northland | 8 | 6 | 2 | 62 | 8.2 |
| Otago | 7 | 1 | 3 | 22 | 2.9 |
| South Canterbury | 4 | 1 | 1 | 26 | 3.4 |
| Southland | 2 | 15 | 5 | 30 | 4.0 |
| Tairawhiti | 4 | 6 | 3 | 35 | 4.6 |
| Taranaki | 5 | 6 | 3 | 32 | 4.2 |
| Waikato | 18 | 25 | 11 | 129 | 17.0 |
| Wairarapa | 1 | 1 | 2 | 9 | 1.2 |
| Waitemata | 4 | 1 | 20 | 2.6 | |
| West Coast | 5 | 4 | 19 | 2.5 | |
| Whanganui | 5 | 1 | 3 | 16 | 2.1 |
| Total for year | 120 | 119 | 84 | 758 | 100 |
*Year runs from 1 July to 30 June. Data extracted from ESR's EpiSurv on 5 May 2006
Data from ESR in Table 2 shows that the two most dominant occupational groupings are meat processing and farmers (including those involved with farming operations).
| Occupational Group | 1997-98* | 1998-99 | 1999-00 | 2000-01 | 2001-02 |
|---|---|---|---|---|---|
| Meat Processing | 22 | 20 | 21 | 37 | 51 |
| Farmer & related | 22 | 22 | 38 | 38 | 51 |
| Contractor/Tradesman | 3 | 2 | 3 | 2 | 3 |
| Forestry | 0 | 2 | 1 | 2 | 2 |
| Professional/Office | 4 | 1 | 7 | 2 | 2 |
| Not Employed | 4 | 4 | 1 | 4 | 5 |
| Other | 2 | 1 | 2 | 4 | 0 |
| Unknown | 7 | 9 | 13 | 11 | 10 |
| Total | 64 | 61 | 86 | 100 | 124 |
| Occupational Group | 2002-03 | 2003-04 | 2004-05 | Total | % |
|---|---|---|---|---|---|
| Meat Processing | 55 | 59 | 51 | 316 | 41.7 |
| Farmer & related | 40 | 43 | 23 | 277 | 36.5 |
| Contractor/Tradesman | 0 | 2 | 2 | 17 | 2.2 |
| Forestry | 1 | 2 | 1 | 11 | 1.5 |
| Professional/Office | 2 | 3 | 1 | 22 | 2.9 |
| Not Employed | 5 | 2 | 0 | 25 | 3.3 |
| Other | 3 | 2 | 2 | 16 | 2.1 |
| Unknown | 14 | 6 | 4 | 74 | 9.8 |
| Total | 120 | 119 | 84 | 758 | 100 |
*Year runs from 1 July to 30 June. Data extracted from ESR's EpiSurv on 8 May 2006. Preliminary data (R Pirie pers comm.) indicates that in the year to 30 June 2006 there were 89 cases - 3 more than the previous year with the distribution throughout the year being shown in Figure 2.
Figure 2: Leptospirosis cases notified July 2005 - June 2006
Click here for Description of Figure 2
Source: ESR via R Pirie pers comm. July 2006
Extract EpiSurv reports accessed through www.nzpho.org.nz state that apart from two peaks in October 2005 and in February 2006 the number of cases is in line with the 3 year average.
However in October 2005 14 leptospirosis cases were notified compared to six cases notified in the same month the previous year. The cases were notified from MidCentral (4 cases), South Canterbury (3), Northland (2), and one each from Counties Manukau, Bay of Plenty, West Coast, Canterbury, and Otago DHBs. Among the 13 cases for whom occupation was recorded, six were farmers, five worked in the meat processing industry, one was a possum hunter, and one was a furniture manufacturer. The serovar was identified for eight cases as L. hardjo (7 cases), and L. ballum (1 case).
In February 2006 13 cases of leptospirosis were notified compared to 7 notified cases in the same month of the previous year. Four (30.8%) of the cases were notified from the Hawke's Bay DHB. Occupation was recorded for 12 cases, 10 were farmers, one was a meat worker, and one was an investor. The Leptospira species and serovar was recorded for 12 of the 13 notified cases: L. pomona (7 cases), L. hardjo (3), L. ballum (1), and L. tarassovi (1).
Acceptance of claims by ACC
Data obtained from ACC on the number of claims made in the years since 1991-92 and the number of claims accepted is shown in Table 3. There are areas for further research to ascertain why such a low percentage of claims notified to ESR come through as claims to ACC and secondly why the percentage of claims lodged claims that have been accepted/covered by ACC has declined since 1998 when leptospirosis was included in ACC's Schedule 2
| Year | ACC claims lodged | ACC claims accepted | % ACC claims accepted | ESR statistics | % of ESR cases lodged ACC | % of ESR cases accepted ACC |
|---|---|---|---|---|---|---|
| 1991-92 | 133 | 92 | 69.2 | |||
| 1992-93 | 105 | 79 | 75.2 | |||
| 1993-94 | 68 | 43 | 63.2 | |||
| 1994-95 | 83 | 60 | 72.3 | |||
| 1995-96 | 67 | 49 | 73.1 | |||
| 1996-97 | 49 | 36 | 73.5 | |||
| 1997-98 | 33 | 23 | 69.7 | 64 | 51.6 | 35.9 |
| 1998-99 | 13 | 12 | 92.3 | 61 | 21.3 | 19.7 |
| 1999-2000 | 4 | 4 | 100.0 | 86 | 4.7 | 4.7 |
| 2000-01 | 40 | 23 | 57.5 | 100 | 40.0 | 23.0 |
| 2001-02 | 69 | 48 | 69.6 | 124 | 55.6 | 38.7 |
| 2002-03 | 88 | 53 | 60.2 | 120 | 73.3 | 44.2 |
| 2003-04 | 95 | 56 | 58.9 | 119 | 79.8 | 47.1 |
| 2004-05 | 101 | 54 | 53.5 | 84 | 120.2 | 64.3 |
| 2005-06 ** | 63 | 27 | 42.9 |
Notes:
Year is the financial year beginning 1 July and ending 30 June
* These are all notifications - from both employees and members of the public.
** 2005-06 is partial year commencing 1 July 2005 ending 13 May 2006
Source of ACC data is Incite 03055 Leptospirosis stats
Produced by Data Warehousing & Business Intelligence Unit
Data Warehouse load date is 13May2006
ESR data extracted from ESR's EpiSurv on 5 May 2006
Some idea of the cost to the individual and the nation
A range of difficulties are encountered when estimating the cost of leptospirosis to the individual and the nation. Some of these include:
- The perceived degree of under-reporting of the illness. This can be the result of the variety of severity of symptoms, the reluctance of the person to go to a doctor, whether or not the doctor recognises the risk of leptospirosis and asks for a blood test for leptospirosis, the accuracy of the blood tests when taken, the reluctance of the person to take time off work because of the impact of extra work load for fellow workers, or because not wanting to forego income. Estimates of the degree of under-reporting vary from a factor of 2 to a factor of 8 to 10 to "all you see is the tip of the iceberg". Implementation of an active surveillance programme in Hawaii resulted in an approximately six-fold increase in reported leptospirosis infections (Sasaki et al., 1993).
- The variability of time required to recover from the disease can be from 3 - 4 weeks away from work up to a period of 6 - 8 months. Longer periods have been recorded, in some cases.
- The percentage of people requiring hospital treatment and for different durations.
- The varying percentage of lodged claims that are accepted by the ACC for compensation.
Since the release of the Guidelines in 2001 there have been on average some 112 cases reported each year.
Data from the meat industry indicates that on average each case results in 6 weeks away from work, excluding time on alternate duties - thus 40 hours/week x $25/hour = $6,000 per person affected.
It is estimated that on average each case costs some $1,500 in direct medical costs when hospitalisation is taken into account with some 45% of those whose affected requiring hospital treatment.
There is no comprehensive data on the actual cost to those engaged in the farming sector or other occupational groupings. More details of the costs to farmers and other self-employed persons needs to be obtained. However, it can be implied that on a conservative basis the cost per person is $7,500 ($6,000 + $1,500) and hence an annual direct cost for 112 persons is of the order of $840,000 per year. The absence of comprehensive and accurate data significantly inhibits the calculation of the total costs of leptospirosis and the hence the benefits and return on various preventive strategies. Note that it is normal to regard the indirect costs of workplace injuries, illness and absence as being 4 to 8 times the direct costs.
Changes in species and/or serovars and routes of transmission.
A major development in the period 2001 to the present has been the research into the epidemiology and control of leptospirosis in New Zealand farmed deer conducted by Professor Peter Wilson and colleagues at Massey University and Colin Mackintosh at AgResearch, Invermay (Wilson et al 2005). This was one of a number of papers on this topic presented to the conference of the Deer Branch of the New Zealand Veterinary Association in 2005.
By taking some 20 blood samples from each of 113 farms in different areas throughout New Zealand the researchers established that L. hardjo was present in 65% of the herds, L. pomona in 4% and a further 14% of herds had both L. hardjo and L. pomona, - with no evidence of infection being observed on 17% of the farms. No serological evidence of serovar L. copenhageni was observed on any farm. In an earlier study in1992-1993 the prevalence of the different serovars was 70% L. hardjo, 10% L. pomona, and 1% L. copenhageni.
As far as is known there have been no recent comprehensive surveys of the occurrence of leptospirosis in dairy cattle. Discussions with the veterinarians practising in the Waikato indicate that some 90% of their clients vaccinate their dairy cattle. Since the middle 1980s the Westland Dairy Company has paid for the vaccination of dairy cattle owned and farmed by its suppliers.
The New Zealand Veterinary Association's product LeptospureTM is a farm specific risk management plan which incorporates the vaccination of all classes of stock at the appropriate times together with effective strategies for hygiene and personal care, rodent control, and waterways and effluent management. A business plan has been developed and resourced by the NZVA with the objective of expanding the uptake of the programme from the current level of some 500 farms to having 8000 dairy farms enrolled in the programme within five years. While the concept of programme is equally applicable to beef cattle, and there was an initiative to apply it to properties in the Taupo area, there has been minimal uptake by beef cattle farmers of either the LeptospureTM or any other leptospirosis vaccination programme.
Vaccination of all pigs for leptospirosis is encouraged as this has been shown to improve productivity by preventing abortion in the sows and to enhance growth rates in baconers, and porkers. Most major pig processing companies will not accept stock from properties which cannot produce a vaccination certificate.
Understanding of the proportion of sheep flocks that are infected with leptospirosis, the degree of infection, and the regional distribution of infected flocks is severely limited by the absence of any comprehensive data. Staff at Massey University are seeking funding to research the production effect of leptospirosis in lambs, and older sheep, and the efficacy of vaccination in controlling leptospirosis at the sheep farm level.
Another aspect of the proposed research initiative is to see if vaccination of all cattle and deer on the property will significantly reduce the infection in sheep on that farm? Preliminary research has confirmed that all young animals are born seronegative therefore any seropositive animals have become infected during their lifetime. While the level of infection in lambs is relatively low the degree of infection can increase very significantly with hoggets and some categories of older sheep (C Heuer pers. comm.).
Thornley observed that in the period 1996-1998 infections caused by L. ballum had overtaken those caused by L. pomona as the second most commonly recognised serovar. As L. ballum, which is maintained in rodents and occurs secondarily among livestock animals, had been tested for in New Zealand for a long period the point was made that the observed increase was not because of a change in testing schedules. Therefore the emergence of it as a more frequent cause of human infection suggested a change in the prevalence of L. ballum and the increasing exposure of people to this serovar by direct animal contact or through contaminated surface waters (Thornley 2002).
However it would appear that this was a temporary shift as the predominant serovars among laboratory reported leptospira over the 2001 - 2003 period were L. hardjo (42.7%), L. pomona (33.5%) and L. ballum (10.7%) with smaller contributions from L.tarrassovi (7.9%) and L.copenhageni (2.4%) (Baker 2004).
There is no consolidated information available on the degree of leptospira contamination of rivers and streams used for recreational purposes by kayakers, trampers, and other users. Although it has been suggested that this might be an increasingly important source of infection the information collected in the various systems lacks the specificity to justify or refute this claim.
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