Legionella is a gram negative bacterium which is commonly found in fresh water. Prior to l976 the organism had not been identified until an outbreak of acute febrile respiratory illness occurred among members of the American Legion who were attending an American Legion conference at a hotel in Philadelphia.

Retrospective documentation indicates that the organism caused human disease at least as early as 1947, and in all probability much earlier than that considering the ubiquitous nature of the bacterium. Legionella pneumophila is the particular strain of Legionella which caused the outbreak in Philadelphia in 1976, and which causes the illness which has come to be known as Legionnaire's Disease. L. pneumophila has been isolated from environmental water sources such as lakes and creeks, as well as from man-made water systems such as cooling towers, evaporative condensers, shower heads, hot water tanks, spas, and ultrasonic nebulizers. System conditions such as warm temperatures and high nutrient levels typically cause proliferation of the organism once the bacterium has "seeded" a particular water system.

Hospital cast off Legionnaire's Disease, known as nosocomial Legionella, infections, are often associated with the potable water system. Disease causing exposures have been documented from aerosols generated by running water taps and shower heads and rinsing ventilation equipment in non-sterile tap water. Further-more, fatal, extra-pulmonary infections from cleansing post-cardiovascular surgery wounds with non-sterile tap water have also been documented.

Whereas sporadic cases of Legionnaires Disease are not uncommon, and are probably under-reported, outbreaks of Legionnaire's Disease are typically associated with buildings such as hotels and particularly hospitals. The organism is an opportunistic pathogen so that exposure presents clinical symptoms almost exclusively in immuno-compromised individuals. In the wild the bacterium replicates by invading waterborne protozoa and commandeering intra-cellular macromolecules to accomplish intracellular multiplication. Following the intracellular replication phase, the organisms lyse the host cell (the protozoa) and re-invade new hosts. In immuno-compromised humans the organism is usually inhaled as an aerosol and after penetrating to the lower lung reproduces intracellularly in the alveolar macrophages finally resulting in pneumonia. Legionella pneumophila caused pneumonias can usually be effectively treated with erythromycin.

While it is probably impossible to permanently eradicate Legionella from water systems, maintenance and administrative interventions will decrease the likelihood of exposure and subsequent disease. Cooling towers must be maintained in a manner that will minimize accumulation of bio-film with its associated nutrients. While cooling towers are commonplace in Hong Kong, there are no cooling towers at HKUST.

Routine and systematic treatment of cooling tower water with biocides is recommended (chlorine being the treatment method with the best track record to date). Plastic, and particularly rubber type components within the potable water system, particularly hot or tepid systems, seem to allow multiplication of the numbers of the organism. Replacement of these components with non-plastic parts is preferred where possible. New materials which resist microbial growth are becoming available on the market.

Maintaining hot water storage temperatures at or above 1310F, and 1250F or more at the tap is recommended. Contact between hot and cold water pipes should be prevented by separation or insulation. If Legionella have colonized a potable water system and disease has been documented from exposure to this water then continuous feed chlorine injection seems to be the chemical treatment of choice. If this approach is chosen care must be given to maintain the optimum pH range for the water and ensure chlorine levels are not excessive which can damage water system components. Generally speaking, a thorough and systematic preventive maintenance program for all water systems will control Legionella populations optimally.

All servicing or maintenance of the heating, ventilating, and air-conditioning equipment (HVAC) including inspections, water testing and applications of biocide treatments must be documented. Furthermore, it is recommended to drain and mechanically clean the interior of cooling towers at least once annually. If cooling tower units are only used during the summer they should be cleaned and treated prior to the first summer start-up. For others cleaning and treatment should at least be in accordance with the manufacturers recommendations. Some success in maintaining trouble-free cooling towers has been claimed from routinely alternating types of biocides used to treat the tower water. At a minimum, cooling towers should be drained and cleaned before restarting whenever they have been out of operation for any extended period of time L> 1 0 days). Monthly total plate count sampling for heterotrophic bacteria is recommended as an indicator of water cleanliness for all cooling towers as part of the preventive maintenance program.

As far as the tap water is concerned, even though Legionella bozemanii has not been implicated as a disease causing strain of the organism efforts should be made to prevent respiratory exposure of immuno-compromised to the aerosol, since it is not clear whether or not any strains of the organism can be categorically described as non-pathogenic. It may be that the location of the tap in relation to the patient bed would preclude such an exposure. Nursing staff should never use tap water for rinsing or cleaning any respiratory therapy equipment, or for cleaning wounds, but should use sterile water for all such applications. Since the organism that caused a fatal post surgery infection was detected in the recovery room tap water it is likely that it was present throughout the system even though it was not detected in any other tap water samples. The organism was detected at a low concentration in the recovery room tap water sample so that the concentration in the whole system was probably low. The recovery room was vacant and the tap may have been unused for some time thus allowing the organism to proliferate to a detectable concentration. A remedial intervention in such a case would be to raise the temperature of the hot water system. However, if the hot water pipes are un-insulated and the cold water pipes are close enough, the cold water pipes may be heated to a point where the organism will proliferate in the cold water lines. A second option would be to install a chlorine injection system for the building water (although this can shorten the lifespan of the pipes).

(This selection has been taken from January, 1994 issue of SafetyWise)

Background
Recently, there have been several cases of human influenza which were apparently caused by an H5N1 (Hemagglutinin-5, Neuraminidase-1) influenza virus. This is a Type A influenza virus and is more commonly associated with poultry and other species of birds. Avian influenza virus can infect a wide range of birds, but during the investigation so far the H5N1 virus has only been isolated from domestic chickens. From an occupational health point of view, the fact that the HKUST Animal Care Facility houses a number of chickens raises some questions relating to safe handling procedures. Professor T.W. Wong, our Occupational Medicine Consultant from the Department of Community and Family Medicine CUHK, provided the following information:

Influenza and its Treatment
Influenza, commonly called "flu" is a highly contagious respiraory disease. The typical clinical features of influenza include fever, chills, headache, dry cough, running or stuffy nose, sore throat and muscle aches. Consult your doctor if you have any signs of the “flu” and breathing or heart problems. The most effective drugs to treat type A influenza are Amantadine and Rimantadine. They can reduce the severity and shorten the duration of the illness among healthy adults when administered within 48 hours of illness onset. Both of these drugs are only available by prescription.

Vaccination
Vaccination is recommended for groups of people at high risk of having medical complications from influenza. These include the aged group, children and teenagers, people with chronic disorders of the lungs or heart and women who will be 6 or more months pregnant or who will have just delivered during the influenza season.

Latest on H5N1 (at the time of publication)
No clinical cases of disease associated with H5N1 infection have been reported in workers contacting birds regularly, such as market workers or poultry farmers. In most of the cases of H5N1 infection there is no evidence of direct contact with poultry or other birds. At present, it is not known how the human cases became infected with the virus, and therefore the following guidelines are based on normal hygiene practices and the predicted behaviour of the virus:

1. Where possible, minimise direct contact with birds.
2. If contact with birds is unavoidable, wash hands thoroughly with soap and warm water after handling them. Disposable plastic or rubber gloves may be worn when handling bids or cleaning and handling cages. After the gloves are removed wash hands thoroughly with soap and water. (The Animal Care Facility has already implemented this protocol.)
3. When visiting poultry farms wear additional protective clothing (such as overalls or gowns) which should be removed on leaving the farm.
4. Staff handling bird carcasses or collecting samples directly from birds are advised to wear paper face masks and appropriate protective clothing.
5. Avoid working for prolonged periods in confined spaces with birds, especially if ventilation is poor.
6. If a fever or respiratory disease develops contact a doctor immediately for appropriate treatment and investigation. Inform your doctor of the history of exposure to birds.

Influenza Virus
Virions are Usually roughly spherical and about 200nm in diameter. The envelope contains rigid "spikes" of haemagglutinin and neuraminidase which from a characteristic halo of projections around negatively stained virus particles.