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

Gizamba, Jacob Mugoya

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

Master Thesis

2022

Abstract

Background Leptospirosis is an emerging zoonotic infection of global importance. Among humans, the infection is associated with varying clinical manifestations ranging from mild selflimiting febrile illness to severe illness mainly characterized by pulmonary hemorrhagic syndrome and acute kidney injury due to Weil's disease. In addition, leptospirosis presents with symptoms that mimic commonly known infections that cause febrile illnesses such as malaria, influenza, hepatitis, yellow fever, and viral hemorrhagic diseases. This has consequently, led to under-estimation of the burden of leptospirosis hence contributing to it neglected status. The burden of leptospirosis is reported to be substantially high in tropical regions and resource limited settings. In Africa, few countries have data and reports on human leptospirosis and research studies are scarce. In South Africa, the infection is an important underreported public health concern however information on the incidence trend and distribution of the infection is lacking. Yet such epidemiological description is essential for effective prevention of the infection. This study aimed at determining the incidence of Human Leptospirosis from 2010 to 2019, and to compare the incidence based on seasonal and demographic factors in Western Cape Province (WCP), South Africa. Methods The study was a retrospective secondary analysis of all data on ELISA IgM tests that were positive for leptospirosis between January 2010 and December 2019 in WCP, South Africa. Data was obtained from the National Health Laboratory Services (NHLS), where all serological tests on serum samples of patients who are clinically suspected to be having a leptospirosis infection are conducted. All leptospirosis positive results were grouped, and the incidence proportion of leptospirosis estimated according to sex, age, season, and year of occurrence. The provincial population sizes were used as the denominator when estimating the incidence and it was expressed as leptospirosis cases per 100,000 population. Negative binomial regression was used to estimate the effect of sex, year of occurrence and season on the incidence of human leptospirosis over the study period. The results were presented as incidence rate ratios (IRR) with 95% confidence intervals (CI). Results A total of 254 cases of human leptospirosis were recorded by the NHLS in the WCP, South Africa between 2010 and 2019. The highest number of cases was recorded in 2015 (42 cases, 16.5%) and lowest in 2012 (9 cases, 3.5%). The incidence of leptospirosis fluctuated widely across all the 10 years with the annual incidence ranging between 0.15 and 0.66 per 100,000 population and an average annual incidence of 0.40 per 100,000 population. The incidence was significantly higher among males compared to females (0.55 and 0.25 per 100,000 population respectively; incidence rate ratio (IRR) 2.2, 95% CI: 1.66,3.03) and the overall male to female ratio was 2.14:1. The average incidence of leptospirosis was highest among the 18-44-year-old age cohort (0.56 cases per 100,000 population), and lowest among the ≤17-year-old age cohort (0.07 cases per 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 incidence proportion in fall, summer and spring seasons were slightly higher compared to what was observed in winter season. However, and there was no significant association between season and incidence of leptospirosis. Conclusions The incidence of leptospirosis widely fluctuated between 2010 and 2019, with males and those above 18 years of age substantially at risk of infection. The results show that leptospirosis is an important zoonotic disease within the province and potentially disproportionately affecting males and the productive age demographic groups. These findings emphasize the need to enhance targeted prevention strategies and provoke further investigation on the importance of environmental and socioeconomic factors on the occurrence of leptospirosis within Western Cape Province and South Africa at large.

Keywords

Public Health

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