Monochloramine for controlling Legionella in biofilms: how much we know?

Prevention of Legionella in water system is a challenge especially when biofilm is present. Hospitals, in particular, deal with vulnerable population requiring additional protection against Legionella. Monochloramine (MC) has been used for small-scale hospital systems in Europe and the US only recently. This review focuses on Legionella in biofilm touching major practical challenges with water disinfection using MC. To date there are no published reviews on this topic so a critical and comprehensive update on the progress in the field was necessary. Scientific databases were reviewed for articles published between 1980 and 2013, containing the terms ‘Legionella’-‘Legionellosis’-‘Legionnaires’ Disease’ and ‘Biofilm’ and ‘Disinfection’-‘Legionella’ and ‘Monochloramine’. In total, 36 articles were considered and divided in 5 groups to evaluate: (i) MC biofilm penetration, residual concentrations, production of disinfection by-products; (ii) influence of pipe material on biofilm formation and disinfectant penetration; (iii) effect of nitrification on MC decomposition rate; (iv) MC treatment and VBNC state of L. pneumophila in biofilms; (v) influence of protozoa on MC disinfection of biofilm. Among the antimicrobial agents, MC appears more effective for decreasing Legionella within the biofilms in vitro and in plumbing systems.