9
Presentation
Legionellosis-especially Legionnaires’ disease—is a leading cause of
disease,disabilityanddeath indevelopedcountries.
Legionella
,apathogenic
bacterium, was identified in 1977 as the causative agent of legionellosis.
Premiseplumbing,includingbothpotableandnon-potable(utility)building
water systems, isnow recognized as theprimary sourceof legionellosis.
Buildingwatersystemshavecharacteristicsthatmakethemparticularly
susceptible tomicrobial colonization.Complexnetworksof relatively small
diameter pipes provide high surface-to-volume ratios, where water can
stagnate for long periods. Water heaters and other necessary processing
equipment furthercomplicatebuildingwatersystemsandcanchangewater
inways that affect
Legionella
.
Legionella
contamination of building water systems is primarily
a function of natural biofilms, the complex heterogeneous microbial
ecosystems thatdeveloponvirtuallyall surfaces incontactwithnon-sterile
water.
Legionella
from colonized plumbing can enter the environment
when pieces of biofilm exit the system through a tap and are broadcast in
bio-aerosols.
Legionella
-parasitizedprotozoamaybe similarly releasedand
disseminated.When theairborne, virulentparticlesenterdeep into thegas-
exchange regionsof the respiratory systemof a susceptiblehost, they infect
and replicatewithin alveolarmacrophages, causingLegionnaires’ disease.
Nearly40yearsofresearchon
Legionella
and legionellosishasexpanded
our understanding, and there are a number of aspects for which there is
broad scientific consensus.
• Parasitized protozoa that graze on biofilm play a defining role in
Legionella
virulence, amplification and transmission.
