Breathe easy - chances are you'll never catch it
Education secretary Michael Suen Ming-yeung was among 17 reported cases of legionnaires' disease last year, the seventh straight year in which case figures have hit double digits.
Legionnaires' disease, a form of pneumonia, was made a notifiable disease in Hong Kong in March 1994, but previously the number of annual cases could be counted on one hand, according to statistics from the Health Department.
Suen is believed to have contracted the illness from his private washroom at the new Tamar government headquarters, which has been found to be contaminated with bacterium that causes the disease.
Should we be worried?
'We need to be aware of the disease, but there is no reason to be overly worried about it,' says Dr Samson Wong Sai-yin, an assistant professor at the University of Hong Kong's microbiology faculty.
'The disease is not common,' says Professor Sian Griffiths, chairwoman of Hong Kong's Prevention of Legionnaires' Disease Committee and director of Chinese University's school of public health and primary care. 'Often, patients have other pathologies and usually recover.'
Further, the disease is not transmitted by person-to-person contact, eating or drinking, according to a Health Department spokesman.
Wong says the apparent increase in the number of confirmed cases reflects 'a much easier and more sensitive diagnosis' that was introduced to government laboratories in 2005.
In the past, the disease could be confirmed by only either culturing the responsible bacterium, Legionella pneumophila, from the respiratory specimens (such as phlegm) of patients, or showing an increased level of antibodies against the bacteria in the blood of patients. Both tests were rather insensitive and tedious.
The latest test, says Wong, looks for the presence of legionella antigen (certain molecules from the bacterial cells) in urine, which has been shown to be very sensitive in picking up the infection.
'Therefore, with this sensitive test, and more doctors being aware of the disease - and hence request the test more often - we are picking up more cases,' he says.
The Health Department spokesman noted that a rising trend of legionnaires' disease has been reported by a number of countries, such as the US (from 0.39 to 1.15 per 100,000 from 2000 to 2009) and Britain (from 0.31 in 2000 to 0.61 in 2009).
'The annual notification rate in Hong Kong [0.53 in 2010] is lower than countries, like the US and Britain, and all reported cases were sporadic cases without evidence of outbreak,' the spokesman says.
An outbreak in July 1976 among delegates attending an American Legion Convention in Philadelphia first brought attention to the disease. More than 200 cases were reported and 34 people died. Medical investigations identified the previously unknown bacterium, which was subsequently named Legionella pneumophila.
Wong says the bacterium is ubiquitous in the environment in fresh water, and can often be found in places such as cooling towers, potable water systems, decorative fountains and whirlpools.
Infection usually occurs when the bacterium enters a person's airways, such as inhalation of contaminated tiny water droplets while taking a shower or walking past a fountain.
The Health Department spokesman adds that infection may also occur when handling garden soil, compost and potting mixes. The bacterium grows well in water at temperatures between 25 and 40 degrees Celsius.
'Most of us will be exposed to the bacterium once in a while, but very few of us will come down with the disease,' he says. 'It's only the high-risk people who are likely to develop the disease after exposure.'
This group includes organ transplant recipients, smokers, the elderly, those with chronic lung diseases, people with suppressed immune systems (such as cancer patients), diabetics, alcoholics and renal failure patients.
Disease can manifest in two ways, Wong says. One is Pontiac fever, a flu-like illness that is self-limiting (in other words, nothing worse than diarrhoea or a cold). Unless it is part of an outbreak investigation, Wong says, most patients will not be diagnosed because the disease is rather mild and most clinicians will not specifically test for Legionella.
'The more classic disease is legionnaires' disease,' he says.
However, because its symptoms and manifestations are similar to other causes of pneumonia, Wong says the disease is not always distinguishable without further laboratory testing. It is generally believed that the disease causes a more severe form of pneumonia, resulting in death for 13 to 33 per cent of patients.
As there is no vaccine for the disease, prevention is key. Wong recommends the following:
At home, make sure that water taps and shower heads are clean and not clogged by scales. Change them if they're blocked. Ensure your building's water tanks and pipes are cleaned regularly.
High-risk individuals should take caution when using humidifiers at home. Clean and disinfect such equipment regularly. There have been cases of infection from humidifiers colonised by bacteria.
Owners of cooling towers and freshwater facilities should maintain them regularly.
Frontline health-care workers should be aware of the possibility of infection when working with a patient with pneumonia, and investigations should be performed when in doubt. This is especially important for high-risk patients so that the correct medication can be given in time.