The association between antibiotic use in hospitals and residual antibiotic concentrations in hospital effluents: a pilot study.

Objective: To analyse the possible association between hospital antibiotic use and residual antibiotic concentrations in wastewater effluents, with the aim of evaluating wastewater surveillance as a potential alternative antimicrobial use monitoring system (AlAUMS).

Methods: The study was conducted at a Regional Hospital in South Africa and followed an observational, quantitative and correlational design. The hospital use of selected antibiotics was determined using consumption data as a proxy and calculated using the WHO Anatomic Therapeutic Chemical (ATC) and DDD methodology. Selected antibiotics in the hospital effluent were analysed by solid-phase extraction (SPE) and quantified by GC-MS. Spearman's rank correlation coefficient and P values were calculated to determine the possible association between antibiotic use and residual antibiotic concentrations as an AlAUMS.

Findings: The highest mean antibiotic use in the hospital was for oral sulfamethoxazole (6.71 DDD/100 bed days), followed by parenteral cefazolin (3.15 DDD/100 bed days). The highest mean antibiotic concentration in the hospital effluent was for sulfamethoxazole (34.57 μg/L) followed by cefazolin (25.32 μg/L). A strong positive correlation was observed for sulfamethoxazole (Rs = 0.86) and a moderate positive correlation for cefazolin (Rs = 0.50). However, none were statistically significant.

Conclusions: The positive correlation displayed between the use of cefazolin and sulfamethoxazole and their concentrations in wastewater indicates a potential association between antibiotic use and residual antibiotic concentrations in hospital settings suggesting that wastewater surveillance is a promising proxy for conventional antibiotic use surveillance. Further studies are necessary to validate these results before wastewater surveillance can be implemented as an AlAUMS.