Considering the ‘known unknowns’

Dr Nick Hill, technical director of the Water Hygiene Centre, examined some of the continuing areas of uncertainty over the characteristics and properties of different Legionella serogroups, the colonisation levels necessary to cause illness in individuals of varying susceptibility, potential sources, and the materials most likely to harbour the bacterium, and discussed effective methods for killing the organism, and preventing its spread. HEJ editor, Jonathan Baillie, reports.

Dr Hill, who is also the chair of IHEEM’s Water Technical Platform, was the opening speaker at a wellattended seminar held in late July at the Mary Ward Centre in Great Turnstile, close to London’s High Holborn. The London event, which followed an IHEEM seminar focusing on the same issues, and featuring many of the same speakers, held in Leeds earlier the same week, was chaired by public health consultant, and well-known expert on waterborne illnesses and pathogens, David Harper. In the day’s opening presentation, Dr Hill examined in some detail what he dubbed ‘the known unknowns’ in the water hygiene and safety sphere, with a particular focus on Legionella. Clarifying what he actually meant by ‘known unknowns’, he referred to a well-known saying from former US Defence Secretary, Donald Rumsfeld, who apparently famously once opined: “As we know, there are ‘known knowns’ – the things that we know we know, and there are also ‘known unknowns’ – that is to say there are some things we know we don’t know, but there are also ‘unknown unknowns’ – the ones we don’t know that we don’t know.” The Water Hygiene Centre technical director’s presentation would, he explained, focus on the second – the ‘known unknowns’, and how they could best be dealt with in the context of a ‘typical’ hospital water system.

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