Crowded cage homes and partitioned flats have made Sham Shui Po the district with the highest incidence of tuberculosis, experts warned.
Although fewer people are contracting the once-deadly disease, the latest government figures show the patient-population ratio in Sham Shui Po has been the highest of the 18 districts in the past five years.
About 109 out of every 100,000 people in the district suffer tuberculosis, according to the Health Department, much higher than all other districts, including Yau Tsim Mong and Wong Tai Sin, which were second and third with incidence rates of 97.5 and 97.4 respectively.
The president of the Public Doctors' Association, Dr Loletta So Kit-ying, a specialist in respiratory medicine, said crowded environments spread contagion.
'The living space for each individual is not enough,' she said. 'Some people may not know that they should cover their mouth when coughing. This will also facilitate the spreading of germs.'
She said most tuberculosis patients were either senior citizens, who had weaker immunity, or recent migrants.
'Vaccination is not available on the mainland, and so it is much easier to be exposed to the bacteria.'
Community organiser Sze Lai-shan, of the Society for Community Organisation, who focuses on helping Sham Shui Po cage-home dwellers, said residents faced a high risk of infectious diseases.
'Health is a big issue in these cubicles. Ventilation is poor and residents have to share toilets and kitchens.'
She said most tuberculosis patients she knew were elderly people. 'They often have difficulty in walking and need our help to take drugs in public clinics.'
Sze added that besides tuberculosis, dwellers were also prone to develop skin infections and asthma.
The society estimates that about 100,000 Hongkongers live in cage homes or partitioned flats. A typical cubicle has no air-conditioning and is about 50 sq ft, just enough space for a small bunk bed, a tiny desk and a small television.
The latest survey by the society showed that the average temperature inside cage homes or cubicles was 3.9 degrees Celsius higher than outdoors, and could be as high as 41 degrees.
However, the total number of tuberculosis cases in the city has continued to decline. Some 7,673 cases were recorded in 1998 and 5,766 in 2006. Last year, the number dropped to a new low of 5,132.
But So said the city needed to remain vigilant, particularly as more people arrived from the mainland.
The number of new tuberculosis cases among mainland migrants has stood below 100 in the past five years, but the number was rising steadily.
In 2006, there was a record low of 58 cases reported among those who had lived in Hong Kong for less than seven years. But last year, the figure rose back to 80.
Sze said the government should offer better housing for the children of Sham Shui Po, so they could grow up in a healthier environment.
She said that of more than 100 applications the society submitted for public housing on compassionate grounds each year, only a dozen were successful.
'Only those who are very old or very sick would be allowed to move to public housing estates. You have to be literally on the verge of death.'
She said while the government should build more public housing in the long run, it should also offer rent subsidies to the underprivileged in the meantime.
About 152,000 people were on the waiting list for public housing as of March this year, a sharp increase from 129,000 in the same period last year.
The government said it would build 75,000 flats for low-income families in the coming five years.