LEGIONELLA - World Health Organization

10.4.6 Outbreak investigation and notification of disease
Inclusion of specific regulations to deal with responses to outbreaks should be considered. Such
regulations could include provisions for investigations and inspections of devices and documentation
by surveillance agencies; they could also include provisions for additional testing and remedial
(or even precautionary) decontamination of devices.
A number of countries and regions have established mandatory or voluntary systems for
notification of legionellosis, as described in Chapter 9. Such notification can be provided by
clinicians or testing laboratories. In Europe, a notification and surveillance scheme has been
developed to facilitate detection and investigation of travel-associated infections (EWGLINET,
2003; see Chapter 9).
The International Health Regulations (IHR) (WHO, 2005) are a legal instrument designed to
provide security against the international spread of infectious diseases. The regulations incorporate
provisions for notification and public health responses to events of international significance.
Legionellosis is not incorporated in the lists of diseases cited in the IHR (WHO, 2005);
however, any disease event that meets the criteria described in Annex 2 of the regulations
(Serious public health impact, unexpected, likely to spread internationally or likely to result in travel or
trade restrictions) must be notified to WHO following the entry into force of the IHR (2005)
in June 2007. The IHR (2005) also introduces new requirements for the inspection of ships
and the issuing of a ship sanitation certificate which will be relevant to outbreaks associated
with ships (see Chapter 7), when these and other provisions in the regulations could be applied.
Notification systems allow prompt investigation of outbreaks or even single cases. Such investigations
can lead to the identification of sources of illness, implementation of remedial action and
provision of public health advice. As a result, the size of outbreaks and the likelihood of
recurrence can be reduced. In some jurisdictions or circumstances, single cases are investigated,
on the basis that they may be the first reported case of an outbreak. Investigations of nosocomial
cases are considered to be of high importance because of the potential risk to immunocompromised
patients (Lee & Joseph, 2002).
10.5 Outbreak impact and economic consequences
Since the first recognized outbreak of Legionnaires’ disease in Philadelphia, USA (Fraser et al.,
1977), many outbreaks have been reported, often involving health-care facilities (see Chapter 6).
During outbreak investigations and the associated media interest, a more complete picture of
the true number of cases is possible than at other times, because during an outbreak clinicians
tend to do more diagnostic tests, and reporting of cases is more complete. In Europe, the number
of clusters reported to the European Working Group for Legionella Infections (EWGLI) is
also increasing (see Figure 10.1).
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS