Post Lockdown Positivity: Emerging Legionella Species Data

January 2022

In July 2021 the LCA, in conjunction with HSE, PHE and Local Authorities held a webinar aimed at raising awareness of increasing legionella positivity rates post lockdown. The data demonstrated that the average positive rate in the UK had increased by around 2% following the lockdowns in response to COVID 19.

Post the webinar, questions were asked if there were particular species that could have led to an increase. This was data that we, as the LCA, had never been asked to investigate or provide previously. With this in mind we approached the three commercial laboratories in the UK (registered with the LCA) that use MALDI-ToF to confirm down to species level to see if they would share their data.

The data has now been returned by some of these LCA members and we are happy to share some of the headlines:

  • Positive results for over 70,000 samples over a 2 year period were included
  • Over 53% of the results were L. anisa
  • Over 32% of the positives were L. pneumophilia (both SeroGroup 1 and SeroGroup 2-15)
  • Nearly 1% of positives were for L. rubilucens
  • Over 6.5% of the results did not confirm a species type
  • There were over a dozen other species identified in results that accounted for <1% of the data set.

What are the implications of this dataset?

The first line clinical diagnostic tool used to confirm Legionnaire’s disease in the UK is commonly a Urinary Antigen Test (UAT) and this method looks predominantly for L. pneumophilia SG1. Given the data above we could be missing over 70% of the legionella infections in patients. 

It is important to note that both L. anisa and L. rubilucens are both confirmed Human Pathogens and thus have the ability to cause Legionnaire’s disease.

This data is in its infancy and further research needs to take place before any significant changes are considered or undertaken. However, it is clear to see from this data that the prominence of species of legionella, other than pneumophilia, should be considered when undertaking a sampling and analytical plan.