# Effect of Chloramine Disinfection of Community Water System on Legionnaires’ Disease Outbreak, Minnesota, USA, 2024

## TL;DR

Chloramine disinfection of a community water system in Minnesota stopped a Legionnaires' disease outbreak by eliminating Legionella bacteria.

## Contribution

The study demonstrates that chloramine disinfection effectively halted Legionella growth in a groundwater-supplied system.

## Key findings

- Before chloramine disinfection, Legionella pneumophila was detected in premise plumbing but not consistently in the distribution system.
- After 24 weeks of chloramine disinfection, all water samples tested negative for Legionella.
- Chloramine disinfection was effective in controlling the Legionnaires' disease outbreak.

## Abstract

The Minnesota Department of Health identified an outbreak of Legionnaires’ disease in a city in northern Minnesota, USA, in April 2023 that continued until chloramine disinfection of the community water system was implemented. Before chloramine disinfection was implemented, Legionella pneumophila was detected in 1 of 16 samples from the drinking water distribution system and in 5 of 10 premise plumbing samples using both cultivation-dependent (Legiolert) and cultivation-independent (digital PCR) assays in this independent investigation. Approximately 11 weeks after disinfection was implemented, all distribution system samples tested negative; however, 1 of 6 Legiolert-tested and 3 of 6 digital PCR–tested premise plumbing samples were positive. After 24 weeks of disinfection, all samples collected from the distribution system and premise plumbing tested negative. Our results show that a community water system supplied by groundwater supported substantial growth of L. pneumophila in premise plumbing and that chloramine disinfection halted the outbreak.