Visible soil as an indicator of bacteria concentration on farmworkers’ hands

Visible soil on farmworker hands has been assumed to indicate microbial contamination that may lead to contamination of produce and illness in the consumer. To test this assumption, we assessed the relationship of visible soil with microbial load on farmworker hands. 78 farmworkers harvested tomatoes for 30 minutes, practiced hand hygiene (hand wash, hand sanitizers) and rinsed their hands in 0.1% peptone solution. Hand rinses were analyzed for turbidity (median Absorbance600nm 0.0815 ± 0.0336 IQR) and microbial load (median log10 CFU/hand ± IQR: E. coli 1.27 ± 0, Enterococcus 3.75 ± 1.66, and coliforms 2.23 ± 1.13). After hands were photographed between hand hygiene and rinsing, they were assigned a “Visible Hand Dirtiness Score” from 0 (no visible soil) to 7 (highly visible soil) (median Score 4 ± 2 IQR). Hand score and turbidity were signi cantly correlated (rho = 0.549, P < 0.001). Hand score and Enteroccocus concentrations were weakly correlated (rho = 0.273, P = 0.015) but not coliforms (P > 0.05) or E. coli (P > 0.05). Our results suggest that while visible hand soil is a good proxy for hand rinse turbidity, visible soil is not a strong indicator for all microorganisms on farmworker hands.

Morrill, V., Aceituno, A., Bartz, F., Heredia, N., Garcia, S., Shumaker, D., ... Leon, J. S. (2018). Visible soil as an indicator of bacteria concentration on farmworkers’ hands. Food Protection Trends, 38(2), 122-128.