A systematic review of the influence of occupational organophosphate pesticides exposure on neurological impairment

OBJECTIVE: The aim of this study was to conduct a systematic review of the published literature and to estimate whether or not there is a causal relationship between occupational exposure to organophosphate pesticides (OPs) and either neurological impairment or depressive symptoms. DATA SOURCES: EMBASE, MEDLINE, Global Health and PsycINFO (1980 to April 2014). SETTING: Observational studies (cross-sectional, cohort and case–control studies) with exposed and unexposed groups. PARTICIPANTS: People who occupationally use OPs for more than 1 month and their family. PRIMARY OUTCOME: Results of neurological core test batteries or depressive symptoms such as headaches, anxiety and dizziness. STUDY APPRAISAL AND SYNTHESIS METHODS: After an extensive search of various literature databases, one author screened titles and abstracts, searched the relevant publications manually and conducted data extraction. All extracted data from the selected articles were synthesised for analysis. Quality appraisal was conducted using the Newcastle Ottawa Scale. RESULTS: Of the 1024 articles retrieved by database search, 24 studies that met the inclusion and exclusion criteria were selected for analysis. Of the selected studies, 17 were cross-sectional and the remaining 7 were cohort and nested case–control studies. The geographical areas included in the studies were the USA (10 studies), the UK (4 studies), Africa (4 studies), Asia (3 studies), Europe (2 studies) and South America (1 study). Each of the included studies used different exposure and outcome assessments such as neurological scores and depressive symptoms, making it difficult to compare the results exactly. Most studies showed that exposed groups had poorer results than unexposed groups; however, owing to the inconsistent neurological test batteries, there was not enough pooling evidence to conduct a meta-analysis. CONCLUSIONS: The findings of this literature review indicate that it is necessary to standardise the neurological or neuropsychological test battery and methods of measuring exposure to OPs.