Crook B, Young C, Rideout C and Smith D
Highlights:
- All Legionella species are potentially pathogenic, but L. pneumophila is usually the primary focus of testing.
- L. anisa also colonises water distribution systems, is frequently found with L. pneumophila, and could be a good indicator for increased risk of nosocomial infection.
- 565,750 water samples (July 2019- August 2021) were analysed from three commercial Legionella testing laboratories.
- Results confirmed that L. anisa commonly colonises water distribution systems, being the most frequently identified non-L. pneumophila species.
- The proportions of L. anisa and L. pneumophila generally remained similar, but increases in L. pneumophila during COVID-19 lockdown suggest static water supplies might favour its growth.
- Disinfection of hospital water systems was effective, but re-colonisation did occur, appearing to favour L. pneumophila; however, L. anisa colony numbers also increased as a proportion of the total.
- While L. pneumophila remains the main species of concern as a risk to human health, L. anisa’s role should not be underestimated, either as a potential infection risk or as an indicator of the need to intervene to control Legionella’s colonisation of water supplies.
