Jump to the beginning of content

LCQ4: Legionnaires' Disease

Following is a question by the Hon Tam Yiu-chung and a reply by the Secretary for the Environment, Transport and Works, Dr Sarah Liao, in the Legislative Council meeting today (May 2) :


It has been reported that, among some 3 000 water samples taken from cooling tower systems of buildings and tested by the Hong Kong Productivity Council's laboratory since 2004, nearly 30% were found to have Legionella pneumophila. In this connection, will the Government inform this Council:

(a) of the respective numbers of persons infected with Legionnaires' Disease ("LD") and died as a result in each of the past three years;

(b) whether it had regularly taken and tested water samples from cooling tower systems of buildings in the past three years; if it had, of the annual number of water samples taken for testing, and the number of cooling towers the water samples from which were found to have Legionella pneumophila in excess of the prescribed standard; and

(c) whether it has plans to take measures to enhance the prevention of LD (including taking and testing more water samples from cooling tower systems of buildings for testing, enacting legislation to require owners of such systems to cleanse and disinfect their facilities on a regular basis, etc), so as to safeguard public health?


Madam President,

Legionnaires' disease (LD) is caused by bacteria Legionella pneumophila, which is found in the natural environment, such as lakes, rivers, ponds and soil.  It also exists in water supply systems such as cold and hot water systems and cooling towers. LD is mainly acquired by inhalation of airborne droplets and mist contaminated by the bacteria but the infection rate is very low. There is currently no evidence that LD is transmitted by person-to-person contact or by eating or drinking.  However, patients who are immunocompromised, smokers, alcoholics, the elderly (aged over 50) and males are more susceptible to this disease.

(a) The number of diagnosed and reported LD cases and the number of consequent deaths in each of the past three years are as follows:

Year    No. of cases of infection       No. of deaths
----            -------------------------               -------------
2004               3                                   0
2005              11                                  1
2006              16                                  3
2007*              2                                  1
*As at April 23, 2007

(b) The Electrical and Mechanical Services Department (EMSD) launched a cooling tower inspection programme in Hong Kong in 2001 with a view to collecting information on and taking water samples from cooling towers throughout the territory to find out their operating conditions. The programme was completed in 2005.  During the programme period, the EMSD collected information on some 12,000 cooling towers and some 10,000 water samples (Note 1) for testing their bacterial content. The number of water samples taken throughout the programme and the number of water samples exceeding acceptable level (Note 2) in terms of their bacterial content are as follows:

                                 No. of water samples
                               excedding the acceptable
                 No. of        level in terms of their
Year    water samples    bacterial content
----             -------------    ------------------------
2001           74                   1
2002        4,587                 426
2003        2,966                 310
2004        1,130                 101
2005        1,300                  54
Total      10,057                 892

Among the 10,057 water samples taken from the cooling towers, 892 (Note 3) of them exceeded the acceptable level in terms of their bacterial content. The cooling towers in question were cleansed and disinfected immediately. The EMSD also notified all the persons-in-charge of the cooling towers of the test results and asked them to pay attention to the operation and maintenance of the cooling towers.

(c) LD is a statutory notifiable disease in Hong Kong. The Centre for Health Protection (CHP) of the Department of Health conducts detailed epidemiological investigations on every LD case. The CHP also conducts joint visits with the EMSD to the places where a patient has stayed before the onset of LD, including his home, workplace and the shops he has patronized, to trace the suspected source of infection and collect environmental specimens for analysis.

It is well documented that cooling towers were sources of LD outbreaks overseas. However, the reported cases of LD in Hong Kong were sporadic which made it very difficult to confirm the sources of infection. The Government has no plan to enact legislation that requires the owners of cooling towers to cleanse and disinfect the facilities regularly. The EMSD will collect water samples from cooling towers to find out their operating conditions.

Regarding the prevention of LD, the Government set up the Prevention of Legionnaires' Disease Committee in 1985. The Committee published the first edition of the Code of Practice for the Prevention of Legionnaires' Disease in 1994 to provide reference to the industry on LD prevention. Subsequent reviews or revisions have been carried out from time to time and the updating of the latest edition will complete at the end of 2007. The Committee also organises seminars and discussions to attract local and foreign experts on LD prevention to deliver subject talks while its members frequently attend seminars held in other regions to exchange views with overseas experts. In 2006, the EMSD published a code of practice on the use of evaporative cooling towers, in addition to organising talks, to help the industry design, operate and maintain cooling tower systems properly.

To safeguard public health, the EMSD writes to owners of cooling towers regularly to remind them to pay attention to the operation and maintenance of the cooling towers.

(1) As some of the cooling towers were installed on externals walls or canopies, or had ceased to be used, water samples could not be taken for laboratory testing.

(2) It is recommended in the technical guidelines of the Occupational Safety and Health Administration of the U.S. Department of Labor, that cooling towers have to be cleansed and disinfected when the concentration of Legionella pneumophila exceed 1,000/ml.

(3) The EMSD and the Hong Kong Productivity Council (HKPC) presented in a different way the discovery of Legionella pneumophila in water samples taken from cooling towers. The HKPC published the number of all water samples containing Legionella pneumophila whilst the EMSD considered that only water samples with Legionella pneumophila concentration exceeding 1,000/ml should be regarded as exceeding the acceptable level. This resulted in the disparity in their findings.

Ends/Wednesday, May 2, 2007