How the ongoing global pandemic drives Legionella concerns

Even before COVID-19, Legionella had the distinction of being one of the leading water- borne disease agents in the USA, with reported cases growing more than 5-fold from 2000-2017 (CDC). But now, as COVID-19 and stagnant water due to building closures collide, the threat increases.

What is Legionella?

Legionella bacteria occur naturally in warm, freshwater environments, like lakes and streams. They become problematic to health when they grow in plumbing systems, particularly where biofilm has developed on pipe walls, and then spread as water is distributed throughout the building. To cause infection, Legionella must be aspirated making showerheads, water fountains, cooling towers, and, less commonly, taps and drinking fountains points of contamination. In high risk populations, Legionella infection can cause a serious type of pneumonia. The simplest way to prevent infections is to keep Legionella out of building water systems.

Ultraviolet (UV) disinfection is a proven solution for preventing Legionella contamination of building water systems, and is suitable for:

  • Hospitals and healthcare facilities
  • Schools
  • Office and commercial buildings
  • Homes

We're here to help. Ask us what kind of UV system is best for your needs.

UV can be applied at the point-of-entry as a complementary disinfection barrier for the whole building or at point-of-use for high risk areas within a plumbing system. Different species of Legionella require different UV dose levels for inactivation. However, in general, required doses are low and well within the operating parameters of our range of UV systems.

Legionella Species 3-log 4-log 5-log
Legionella Bozemanii 3.5 mJ/cm2 4.7 mJ/cm2 5.83 mJ/cm2
Legionella dumoffi 5.5 mJ/cm2 7.33 mJ/cm2 9.17 mJ/cm2
Legionella gormanii 4.9 mJ/cm2 6.55 mJ/cm2 8.17 mJ/cm2
Legionella micdadei 3.1 mJ/cm2 4.13 mJ/cm2 5.17 mJ/cm2
Legionella longbeachae
(found in potting soil)
2.9 mJ/cm2
Legionella pneumophila
(legionnaires disease)
3.8 mJ/cm2 5.1 mJ/cm2 6.33 mJ/cm2
Legionella interrogans
(infectious jaundice)
6.0 mJ/cm2

Controlling Legionella

Routine Legionella testing is not common in the operation and maintenance of many building water systems, with the exception of hospitals and healthcare facilities. But, given the extensive shutdowns and low-level use and occupancy of so many buildings, including schools and offices, testing is strongly encouraged. Where Legionella is detected, the corrective actions include disinfection (thermal or hyper-chlorination) and flushing, followed by repeat testing. UV disinfection can then be employed to avoid re-inoculation of the plumbing system.


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