Investigation and response to an outbreak of leptospirosis among raspberry workers in Australia, 2018

Abstract

Background In 2018, an outbreak of leptospirosis was identified among raspberry workers from a mixed‐berry farm in New South Wales, Australia. Initial testing had not revealed a cause, but eventually leptospirosis was detected via polymerase chain reaction (PCR). Further serological testing detected Leptospira borgpetersenii serovar Arborea, of which rodents are the predominant reservoir. Leptospirosis is rare in Australia, with outbreaks usually related to flooding. We conducted an investigation to identify risk factors for infection, to inform control measures. Methods Cases were detected through laboratory notifications, hospital‐based syndromic surveillance, awareness‐raising among farm employees and clinician alerts. Confirmed cases had a four‐fold rise in antibody titre or single titre ≥400 on microscopic agglutination test, and a positive IgM. Probable cases had a positive Leptospira PCR or IgM, and possible cases had a clinically compatible illness. We conducted a case–control study among raspberry workers on the farm and compared reported exposures between cases and seronegative controls. We assessed environmental risks on‐site and tested rodents for leptospirosis. Results We identified 84 cases over a 5‐month period (50 confirmed, 19 probable and 15 possible). Compared with controls, cases were less likely to wear gloves and more recently employed. Cases also more commonly reported always having scratched hands, likely from the thorns on raspberry plants. We observed evidence of rodent activity around raspberry plants and three of thirteen trapped mice tested positive for Leptospira Arborea. Control measures included enhanced glove use, doxycycline prophylaxis and rodent control. Conclusions This is the largest known outbreak of leptospirosis in Australia. Workers were likely exposed through scratches inflicted during harvesting, which became contaminated with environmental leptospires from mice. Leptospirosis should be considered an occupational risk for raspberry workers, requiring protective measures. Chemoprophylaxis may assist in controlling outbreaks. PCR assists in the early diagnosis and detection of leptospirosis and should be included in surveillance case definitions.

Emerging canine leptospirosis in Sydney and the role of population demographics

“…Other serovars reported in this survey included Canicola, Ballum, Medanensis, Panama, Zanoni, Robinsoni, Javanica and Arborea (Zwijnenberg et al, 2008). In the Sydney outbreak (2017∓2020), the majority of cases and it was also detected amongst rodents (Mus musculus) in the region (Katelaris et al, 2019). This serovar has been previously reported in Australian dogs (Zwijnenberg et al, 2008), but not in those dogs tested from the recent Sydney outbreak (Griebsch et al, 2022).…”

Leptospira Infection in African Green Monkeys in an Endemic Area: An Opportunity for Comparative Studies in a Natural Environment

“…At a given time point, the magnitude of contamination and the potential risk of transmission can be proportionally high, even when a low number of animals are shedding. The handling of contaminated crops has resulted in recent Leptospirosis outbreaks in agriculture workers in Europe and Australia [19,20]. A similar zoonotic threat may exist in this island, warranting biosecurity measures in controlling contamination of agriculture products with AGM urine.…”

Leptospirosis is an emerging infectious disease of pig-hunting dogs and humans in North Queensland

“…All the dogs in this study were considered clinically normal at the time of venepuncture based on an unremarkable physical examination. There is established doctrine in human leptospirosis diagnostic criteria that one titre of >1/400 for a pathogenic serovar is considered diagnostically positive for leptospirosis [16,37]. However, this doctrine hasn't been established in dogs.…”

“…At more than 1.7 million square kilometres, it is roughly 4.8 times bigger than Germany and annually records the highest number of human leptospirosis cases in the country. Although leptospirosis is considered an occupational risk for farmers, veterinarians, meat workers and military personnel, it is increasingly recognised as a risk for campers, white water rafters and those who participate in sport or other outdoor activities in potentially contaminated areas [16]. It is a notifiable disease for human patients in Qld, but not for companion or production animal species [16,17].…”