LEGIONELLA - World Health Organization

of L. pneumophila were isolated from the pool (Rowbotham, 1998). In 2003, there were eight
cases and one death among passengers who had been on a cruise around Iceland. Strains of
L. pneumophila serogroup 1 that were indistinguishable by multilocus sequence typing were
isolated from the hot tub and hairdressing station, but not from anywhere else on the vessel,
and infection was epidemiologically linked with the hot tub (Lai et al., 2004). This latter
outbreak demonstrates the importance of international collaboration to investigate shipborne
outbreaks, since the cases were detected and investigated in Germany after the vessel had
docked there to disembark passengers, and it was investigated in its next port of call, in the
United Kingdom.
Air-conditioning — risk factors
There are no confirmed reports of outbreaks of Legionnaires’ disease associated with airconditioning
systems on ships, but these systems have been suspected in some outbreaks. In
1984, a large outbreak on a cruise ship occurred after the air-conditioning was turned on at
Bordeaux, France. No common source was discovered, but the epidemic curve indicated that
the air-conditioning system contributed in some way to the outbreak (Rowbotham, 1998). In
another outbreak on a cruise ship in 1984, no source was identified, but the outbreak investigation
revealed problems with the air handling units (Christenson et al., 1986). Air-conditioning
systems on ships are dry and do not have evaporative coolers; however, humidifiers (including
food display units) are often installed on ships and could generate aerosols. A study carried out by
Temeshnikova et al. (1996) identified L. pneumophila serogroup 1 in washings from air-conditioning
equipment, and in samples from the mechanical supply and exhaust ventilation equipment
on ships.
7.4 Monitoring
This section should be read in conjunction with Section 3.3.2 of Chapter 3. The steps involved
in monitoring, some of which are discussed below, are to:
• identify control measures (Section 7.4.1)
• monitor control measures (Section 7.4.2)
• validate effectiveness of the WSP.
7.4.1 Identify control measures
Since the introduction of the European Guidelines for Control and Prevention of Travel Associated
Legionnaires’ Disease in July 2002 (EWGLI, 2002, 2003), the number of hotel cases associated
with each identified cluster has reduced, indicating that control measures have been effective
in preventing further cases. In 2004, the proportion of clusters involving only two or three cases
reached almost 90%, compared with 84% in 2003 and 81% in 2002 (John Lee, Health Protection
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS