Keeping a killer in check
Mariana Wan looks at just how big a threat tuberculosis is to our community
The Encyclopaedia Britannica once described tuberculosis (TB) as 'the most serious menace to health in Hong Kong'. Author John Bunyan called the disease the 'captain of all the men of death'.
More than 100 years since Robert Koch identified the bacterium that causes TB, it is still the world's top infectious killer and in recent weeks has become a nightmare haunting many a parent in Hong Kong.
Although the disease has long ceased to be the territory's top killer, 310 people died of it last year.
When four children and a female helper at Fuk Loi Estate Kindergarten in Tsuen Wan were diagnosed with the disease, parents were duly alarmed. The TB 'crisis' escalated when another 12 students from Morning Sun Nursery in Tsuen King Circuit tested positive in a skin test. Parents rushed their children for a check-up. Others demanded that the kindergarten be closed and that children be kept away.
Are such precautions necessary? The rod-shaped bacterium that causes TB can lodge in the lungs (pulmonary TB) or affect organs such as the lymph nodes, bones, joints, kidneys, intestines or abdomen.
Foreign studies show these extra-pulmonary diseases occur in about 25 per cent of children younger than 15 with TB. Of all the infections, tuberculous meningitis (inflammation of the coverings of the brain and spinal cords) is 'undoubtedly' the most devastating if left untreated, said a group of local doctors in a recently published paper. It is also very difficult to diagnose. 'You need to be a wine taster to taste this one,' said a paediatrician.
The development of multi-drug resistant TB - due to poor compliance of patients when it comes to taking their medication - is cited as one reason why the disease with a 6,000-year history is still deadly today.
But figures compiled by the Department of Health show that in 1952, when the incidence of the disease reached its peak, the notification rate by doctors to the Department of Health was 697.2 cases per 100,000 of the population. In 1992, the rate was 112.43 and in 1994, 104.25.
The death rates from TB also show a dramatic fall over the years, from 168.1 per 100,000 in 1952 to 7.1 in 1992 and 6.7 in 1994.
From 1988 to 1993, the average incidence of tuberculous meningitis among the one-to-nine-age group was three per year, 1.3 per year among the 10-to-19-year age group and only one reported case in the under one-year age group. Although no upward trend was detected, the group of doctors led by Kwong Wah Hospital's Dr Daniel Ng, in a recent journal, stressed the importance of early diagnosis 'especially . . . in Hong Kong where we still have a high incidence of pulmonary tuberculosis because of continuous influx of immigrants from China'.
Dr William Chen, chief of service of the respiratory medicine department of Kowloon Hospital, said although Hong Kong did not have a sudden increase in TB cases, the rate of decrease has slowed in the past decade, which he attributed partly to less publicity about the disease.
He stressed the importance of looking after the elderly - the only population sector suffering a rise in the disease.
Professor Lau Yu-lung, president of the Hong Kong Paediatric Society and top paediatrician with the University of Hong Kong, said rather than blaming immigrants from China, the public should be taught the importance of personal hygiene.
'We used to read in primary textbooks that we should not be spitting everywhere . . . That message seems to have been lost in our society.' But he added that the public should realise that not all forms of TB were infectious. 'Those who are infected may be immunologically healthy so their infection may not necessarily progress to disease.' Transmission of TB is most often via the respiratory tract, by inhalation of the bacterium from the sputum of persons with pulmonary TB. Therefore, patients who do not have symptoms of coughing or sneezing are unlikely to infect others.
Infants or children who are exposed to adults with TB affecting the lungs are at risk.
Professor Lau said that the bacterium was a slow-growing micro-organism. This means treatment could take as long as one year in the case of tuberculous meningitis, leading to poor compliance with medication.
Dr Chen said the Government did not invest enough in dealing with patients with a poor compliance to treatment, such as drug addicts.
The fact that a patient had to take his medications for months did not mean he was infectious throughout the course of his treatment, said Professor Lau.
Most adult and adolescent patients are considered to be non-infectious within a few weeks of starting appropriate therapy. Children with pulmonary TB are usually not contagious because their lesions are small, discharge of bacteria is minimal and the cough is minimal or non-existent.
The Department of Health, in handling the Fuk Loi case, has followed international protocol in its pledge to 'trace the source'. Close contacts of the infected children have been investigated.
Since children with pulmonary TB are usually not contagious, the source is almost definitely an adult. It is often vital that children who may have come in contact with the adult source are tested so that preventive therapy can begin.
Professor Lau said that local infants and children who have tuberculosis infection without disease are usually prescribed two to three different kinds of drugs as preventive treatment.
He also warned that although Hong Kong vaccinated all its newborns and school entrants with bacillus Calmette-Guerin (BCG), it did not guarantee immunisation.