The burden of city’s pain treatment – a longitudinal one year study of two cities via wastewater-based epidemiology

This paper explores Wastewater-Based Epidemiology (WBE) as a tool enabling understanding of city’s pain treatment in an intercity longitudinal study. An intensive 13-month monitoring programme was undertaken in two adjacent urban areas in South-West England: a small commuter town Keynsham and the city of Bath. The study has shown a great potential of using triangulated WBE and National health Service (NHS) prescription data in understanding pain treatment in two contrasting communities with strong apparent seasonal patterns of short pain medications vs chronic pain treatment as well as the type of treatment used (e.g. oral vs topical). Community-wide usage of NSAIDs and paracetamol in the intercity study is population size and season driven with the highest usage recorded in winter months. This contrasts with other pain pharmaceuticals, especially those used for chronic pain, where no/limited seasonal usage was recorded. Unmetabolized NSAIDs are, to a large extent, directly disposed of into the sewerage system bypassing metabolism due to their preferred topical application. This is particularly apparent in winter months with naproxen showing the highest seasonal variability. Pharma/met analysis allows for tracking topical (non-metabolic) application/down-the-drain disposal of pharmaceuticals with frequent instances of direct disposal of NSAIDs into the sewerage system observed. Normalisation of pharma markers to population size shows comparable estimates of pharma usage in the two cities confirming population as the main driver of pharma loads in wastewater. Variable application patterns of pain pharmaceuticals make back-calculation of intake more convoluted. Intake calculated using percentage of urinary/faecal excretion of metabolites or parent compounds as consumption markers leads to likely underestimation of NSAIDs usage due their both oral and topical application. Prescription data indicates cumulative internal and topical usage.