LEGIONELLA - World Health Organization

The target levels defined in Box 6.1 are seen as the best way to minimize the risk. The alert
level is designed to ensure that relevant people are informed, and that corrective actions (e.g. a
review of the procedure for maintenance, or new controls) are instigated. When the maximum
level is reached, disinfection of the water distribution system must be organized and the
procedure for maintenance revised. Additionally, an independent body (e.g. local sanitary
authorities) should carry out a new inspection before authorization for reuse is given.
Operationally, control measures, such as temperature, disinfectant residual and pH should be
monitored on line, as discussed in Chapters 4 and 5.
Every case of nosocomial legionellosis constitutes an alert, meaning that other cases may have
occurred or could occur in the future in the health-care facility (which would constitute an
outbreak; see Box 6.2). Where there is a possibility of a nosocomial case, it should always be
investigated.
Box 6.2 Definition of a nosocomial outbreak
A nosocomial outbreak is defined as two or more confirmed cases of legionellosis in the
same hospital or residential institution within a six-month period.
Location of the outbreak is defined in terms of geographical proximity of the cases and
requires a certain level of judgement.
The WSP and system assessment for control of Legionella in the hospital and the maintenance
records must be reviewed by the following people, working together:
• the incident and outbreak management control team
• the person responsible for Legionella control
• the appropriate hospital engineer
• the infection control physician (hospital hygienist).
The aim of the review is to ensure that the preventive procedures identified as necessary to
prevent proliferation of and exposure to Legionella are followed. Any deficiency in the control
procedures should be remedied as soon as possible. Sampling should be undertaken, followed
by precautionary disinfection of parts of the water system, if this is considered to be justified.
The incident and outbreak control management team should always include an expert in
environmental monitoring of Legionella. Researchers should not be confined to the index case;
it is important to also look for other previously undetected cases of legionellosis. The search
should look for other confirmed or presumptive cases of Legionnaires’ disease associated with
the hospital or community, unexplained cases of nosocomial pneumonia in patients (especially
those with impaired immunity), and pneumonia in hospital staff.
00 LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS