Risk factors for human leptospirosis following flooding: A meta-analysis of observational studies

Leptospirosis is probably the most widespread zoonotic disease in the world especially in tropical countries. There has been an increase in individual studies, which assessed the frequency of leptospirosis in flood conditions. Some studies showed contact with floods was significantly associated with the occurrence of leptospirosis while other studies reported differently. The objective of this meta-analysis was to synthesize the evidence on the risk factors which are associated with human leptospirosis following flooding. We set up the inclusion criteria and searched for the original studies, addressing leptospirosis in human with related to flood in health-related electronic databases including PubMed, Embase, Ovid Medline, google scholar and Scopus sources. We used the terms 'leptospirosis', 'flood', 'risk factor' and terms from the categories were connected with "OR" within each category and by "AND" between categories. The initial search yielded 557 citations. After the title and abstract screening, 49 full-text papers were reviewed and a final of 18 observational studies met the pre-specified inclusion criteria. Overall, the pooled estimates of 14 studies showed that the contact with flooding was a significant factor for the occurrence of leptospirosis (pooled OR: 2.19, 95% CI: 1.48-3.24, I-2 : 86%). On stratification, the strength of association was greater in the case-control studies (pooled OR: 4.01, 95% CI: 1.26-12.72, I-2 : 82%) than other designs (pooled OR: 1.77,95% CI: 1.18-2.65, I-2 : 87%). Three factors such as 'being male'(pooled OR: 2.06, 95% CI: 1.29-2.83), the exposure to livestock animals (pooled OR: 1.95, 95% CI: 1.26-2.64), the lacerated wound (pooled OR: 4.35, 95% CI: 3.07-5.64) were the risk factors significantly associated with the incidence of leptospirosis following flooding in the absence of within-study heterogeneity (I-2 : 0%). We acknowledge study limitations such as publication bias and type 2 statistical errors. We recommended flood control and other environmental modifications that are expected to reduce the risk of leptospiral infection, and a multi-sectoral effort to this aspect would have long-term benefits.