Incidence and distribution of human leptospirosis in the Western Cape Province, South Africa, (2010-2019): A retrospective study

Abstract Background Leptospirosis is an emerging zoonosis of global importance. In South Africa, the infection is an underreported public health concern, with limited information on its incidence and distribution. This study aimed to determine the incidence of human leptospirosis from 2010 to 2019 in Western Cape Province (WPC), and to compare the incidence based on seasonal and demographic factors. Methods A retrospective study was conducted with data on leptospirosis diagnoses by sex, age, season, and year in WCP obtained from the National Health Laboratory Services. With the provincial population sizes as the denominator, the incidence of leptospirosis was estimated and expressed as cases per 100,000 population. Negative binomial regression was used to estimate the effect of sex, season, and year on the incidence of leptospirosis. Results A total of 254 cases of leptospirosis were reported between 2010 and 2019, with the highest number of cases being in 2015. The annual incidence ranged between 0.15 and 0.66/100,000 population with a 10-year average incidence of 0.40/100,000 population. The incidence was higher among males than in females (0.55 vs. 0.25/100,000 population; incidence rate ratio (IRR) 2.2, 95% CI: 1.66,3.03). The 18-44 age cohort and had the highest average incidence (0.56/100,000 population), while the ≤17age cohort had the lowest incidence (0.07/100,000 population). The 18-44 (IRR 8.0, 95% CI: 4.65,15.15) and ≥45 (IRR 7.4, 95% CI: 4.17,14.17) age cohorts were more at risk of infection compared to ≤17age cohort. The average incidence of the infection was similar among seasons and there was no significant association between season and incidence of leptospirosis. Conclusions The results highlight that leptospirosis is an important zoonosis within the province disproportionately affecting males and the productive age demographic groups. These findings should enhance targeted prevention and provoke further investigation on the importance of environmental and socioeconomic factors on leptospirosis burden. Author Summary Leptospirosis is an emerging zoonotic bacterial disease of global importance. Despite its wide distribution, the disease is largely underestimated because its clinical manifestations mimic certain commonly known febrile illnesses such as malaria, influenza, hepatitis, and yellow fever. Leptospirosis burden in South Africa has been suggested to be moderately high however studies on the burden of the infection are lacking. This study sought to determine the incidence and trends of leptospirosis in the Western Cape Province, South Africa between 2010 and 2019. Overall, leptospirosis average incidence was 0.4 cases per 100,000 population (ranging from 0.15 to 0.66 cases per 100,000 population). Leptospirosis incidence was highest among male individuals and among those who were aged 18-years and above, however, the incidence did not differ by seasons. These estimates highlight that leptospirosis is an important zoonotic disease within the province and potentially disproportionately affecting males and productive age demographic groups. Therefore, this indicates the need for an all-encompassing One Health Approach to obtain all relevant information concerning leptospirosis distribution and risk factors in South Africa and in Africa at large to effectively enhance leptospirosis prevention strategies.