# Catching the Mardi Gras fever: Quantifying the impact of mass gathering tourism on local bacterial prevalence and community diversity in municipal wastewater

## TL;DR

The study shows how mass gatherings like Mardi Gras impact local bacterial diversity in wastewater, with increased human pathogens and microbiota.

## Contribution

This is the first study to quantify the effect of mass gathering tourism on wastewater bacterial communities using 16S metagenomic analysis.

## Key findings

- Bacterial species turnover was significantly higher in New Orleans during Mardi Gras compared to a control site.
- Alpha diversity in wastewater peaked 2-3 weeks after Mardi Gras Day, with increases up to 1967%.
- Human pathogens like S. enterica and E. coli showed wastewater abundance changes matching clinical isolate data.

## Abstract

We employed 16S metagenomic analysis to measure the impact of Mardi Gras tourism on the bacterial ecology found in New Orleans’ municipal wastewater. Throughout the peak of the 2023 Carnivale season, species turnover was significantly higher in New Orleans than it was in our control site. Alpha diversity metrics peaked 2-to-3 weeks after Mardi Gras Day, increasing between 65% and 1967% over Carnivale. We also found that human pathogens and microbiota had significantly stronger, more positive correlations with the rise in Mardi Gras tourism than did environmental control species. These changes in wastewater abundance for two species – S. enterica and E. coli – mirrored the concurrent clinical isolate data from the same region for Salmonella spp. and STEC. We also found that multiple alpha and beta diversity measures correlated strongly with increases in tourism during the peak of Carnivale season.