Leptospirosis in Aotearoa New Zealand: Protocol for a Nationwide Case-Control Study (Preprint)

BACKGROUND In Aotearoa New Zealand, 90% of cases with notified leptospirosis (a zoonotic bacterial disease) have been men working in agricultural industries. However, since 2008, the epidemiology of notified cases has gradually changed i.e., more women are affected, there are more cases associated with occupations traditionally not considered high-risk in New Zealand, infecting serovars have changed and many patients suffer long after infection. We hypothesise that there is a shift in leptospirosis transmission patterns with a significant burden on affected patients and their families. OBJECTIVE To describe the protocols used to conduct: 1) a nationwide case-control study to update leptospirosis risk factors; and 2) follow-up studies to assess the burden and sources of leptospirosis in New Zealand. METHODS The study used a mixed methods approach, comprising a case-control study, and four sub-studies that involved cases only. Cases were recruited nationwide, and controls were frequency matched by sex and rurality. All participants were administered a case-control questionnaire (Study 1), with cases being interviewed again at least 6 months after the initial survey (Study 2). A subset of cases from high-risk occupations i.e., farmers and abattoir workers, were further engaged in a semi-structured interview (Study 3). Some cases with regular animal exposure had their in-contact animals (livestock for blood and urine and wildlife for kidney) and environment (soil, mud, and water) sampled (Study 4). Patients from selected health clinics suspected of leptospirosis also had blood and urine samples taken (Study 5). Study 4 and 5 blood samples were tested with the microscopic agglutination test (MAT) to test for antibody titres against Leptospira serovars Hardjo type bovis, Ballum, Tarassovi, Pomona and Copenhageni. All blood, urine and environmental samples were also tested with polymerase chain reaction (PCR) analysis for the detection of pathogenic Leptospira DNA. RESULTS Participants were recruited between 22 July 2019 and 31 January 2022 and data collection for the study has concluded. Ninety-six cases and 300 controls were recruited and interviewed for the case control study, 92 cases participated in the follow-up interviews, 13 cases participated in the semi-structured interviews and 4 cases had their in-contact animals and environment sampled. Data analysis for the case-control study and the 6-month follow-up interviews are underway. CONCLUSIONS The methods used in this study may provide a basis for future epidemiological studies for infectious disease. CLINICALTRIAL N/A