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Asthma Prevalence Related to the Environment

Asthma is the commonest chronic childhood disease and a major reason for the admission of children to

hospital. There are approximately 120,000 children in Hong Kong with varying levels of asthma. Forty per cent of them need to visit specialty outpatient clinics from time to time. Those who are subsequently hospitalized make up 15 per cent of all children admitted to hospital. In recent years, the prevalence of asthma has been on the rise. Research at the University shows its prevalence in 1989 to be 4.8 per cent, and the figure rose to 11.2 per cent in 1995.

Higher Incidence Caused by the Environment

Prof. Gary Wong of the Department of Paediatrics pointed out that genetic alterations and environmental factors are the two main causes of asthma. But genes do not undergo major alterations within a period of six years, and while childhood asthma in Hong Kong is less prevalent than that in the West, it is far more prevalent than that on the mainland, which has a similar gene pool. All this indicates that the environment is the main reason for the drastic increase in childhood asthma prevalence in the territory in recent years. Statistics in the UK and Australia also show that childhood asthma has doubled in the past 10 years or so, which further confirms the environmental influence.

Prof. Wong said, ‘Environmental asthma allergens are very complex. There have been very few studies on asthma in Chinese children in the past, especially large-scale studies. In 1994 he conducted a small study comparing the prevalence of childhood asthma in Beijing, Guangzhou, and Hong Kong. The results show that the prevalence of the condition in Hong Kong is three times that in Guangzhou. This study triggered a large-scale comparative study in 1996 to investigate the role played by environmental risk factors. The project was supported by a grant of HK$692,000 from the Research Grants Council and led by Prof. Wong. The other team members included Prof. Fok Tai-fai of the Department of Paediatrics and Prof. Dr. Joseph Lau of the Centre for Clinical Trials and Epidemiological Research.

A Large-scale Comprehensive Study

The study, a collaboration with the Capital Institute of Beijing and the Guangzhou Institute of Respiratory Disease, covered 11,000 children aged 9 to 11 from the three cities. ‘The subjects, who come from different areas of the three places, were selected by random sampling. We asked their parents to give details about the children’s living environment since birth and their allergic reactions, including eye, skin, and nose allergies, whether there is rash and coughing, whether exercise and climate change cause wheezing, etc. The questionnaire is recognized internationally as a reliable tool for measuring childhood asthma, Prof. Wong remarked.

The research team then selected 1,000 participants from each of the three cities for a skin-prick test to observe their response to different allergens. Finally 200 children from each city were arranged to be given an airway sensitivity test. As the two tests were expensive and time-consuming, they could only be administered on a smaller sample. The researchers also conducted an environmental investigation into the homes of these children using standardized appraisal methods. They took samples of house dust from the bed, and the floors of the bedroom, living room, and kitchen, and measured the concentration of allergens using an immunity test.

Prof. Wong explained why no outdoor environmental data were gathered: ‘International asthma research has shown that air quality has no effect on asthma. For example, Chongqing is more polluted than Hong Kong, but the prevalence of childhood asthma there is only a fifth of that in Hong Kong.’

Hong Kong’s Asthmatic Children Double Those in
Beijing and Guangzhou

The study found that the number of local asthmatic children is double that of Beijing and Guangzhou (Figure 1). Factors identified as ‘high-risk’ include home smoking, maternal smoking, use of synthetic pillow and bedding, and use of gas as cooking fuel. ‘A baby whose mother smokes during pregnancy will have a narrower bronchial tube. If it continues to inhale second-hand smoke after birth, its bronchial tube will narrow even further, making it prone to infections and wheezing. Synthetic bedding and pillow contain oil ingredients which slowly release infection-causing and dust-attracting chemical gas. Cooking gas releases carbon monoxide and carbon dioxide, which trigger asthma symptoms, because some of the gases are not completely burnt in the process,’ Prof. Wong explained.

The prevalence of asthma is found to be lower among children who were breast-fed (the longer the better), have siblings in the home, and attend day care centres early on. Exposure to different viruses has been shown to boost their immune system.

Research conducted overseas have shown house dust and cats to be the most common allergens. Over 20 per cent of Guangzhou children are found to be allergic to house dust, compared to only 7 per cent for Beijing (Figure 2). Given the similar prevalence of asthma in the two cities, one can conclude that while house dust is an allergen in China, it is not as significant as in the West. The study also finds that children who are allergic to dust and cats have a three to four times greater chance of suffering from asthma than the normal person. Prof. Wong pointed out, however, that this only shows that these allergens may trigger an attack in asthma-sufferers but not that they cause asthma.

In conclusion, Prof. Wong said, ‘Asthma patients are a heavy burden on Hong Kong’s medical services. If they can learn to avoid certain risk factors in the environment, we can reduce its prevalence more effectively. We will continue to examine the link between environmental factors and asthma so as to find better preventive measures.’

The general misunderstanding that asthma is incurable or uncontrollable has led to neglect in management. Prof. Wong pointed out that although there is still inadequate knowledge of the causes of asthma, medical practitioners are able to treat it. Advances in technology have also raised the efficacy of medication.

Ten years ago, the rate of hospitalization of Hong Kong’s asthmatic children was 25 per cent, but it has now gone down to 10 to 15 per cent.

Prof. Wong said that the condition very often improves as the child grows up, but improper management over an extended period of time can cause permanent damage to the airway. The research team designed an education programme to explain to patients the underlying and precipitating causes of asthma, the rationale of different types of medication, and the proper use of treatment devices. Although there is no lasting cure for asthma yet, the disease can be put under good control with the right medication, which, if administered properly, will have no serious side effects and is not addictive. The condition of patients who have participated in the programme has been shown to have improved significantly, both in the recurrence rate and symptom manifestation. With proper treatment, asthmatic children can live normal and healthy lives.

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