VietNamNet Bridge – Nguyen Thi To Tam and her husband live in Binh Hung Hoa A Ward, a densely populated area in Binh Tan District with some of the highest rates of dengue fever in the city.

One of places in Binh Hung Hoa A Ward, a densely populated area in Binh Tan District with some of the highest rates of dengue fever in the city.— Photo congan

"There are so many mosquitoes everywhere inside and outside my house," she said.

Her house is near vacant housing plots piled with household waste thrown away by local residents, a perfect breeding ground for mosquitoes.

Tam and her husband, who contracted dengue fever about two years ago, said they wanted to move but they cannot afford to live elsewhere.

Like Tam, Nguyen Huu Nghia, who also lives in the ward, is worried about the prevalence of dengue fever in the area.

His house is near the 60-hectare Binh Hung Hoa A Cemetery, which has become a breeding ground for mosquitoes.

"Although the ward's health officials have sprayed chemicals or put salt into flower pots in the cemetery, they still appear about 10 days later in litter like food containers, tin cans and plastic bags, as well as standing water," he said.

The cemetery, which has 80,000 graves, is also home to more than 300,000 residents, most of them migrants from other provinces and cities.

Next year, all of the graves as well as the families who live on the cemetery grounds will be relocated by the city to make way for a residential area and park to be built on the site.

The ward, which was established in 2003, has 106,308 residents, the highest number of any ward in HCM City. More than half of the residents moved from other provinces and cities.

With a population density of 22,862 inhabitants per kilometre, the third-highest in the district, the ward is listed as a high-risk area for dengue fever by the Disease Prevention Centre.

From January to May, the ward reported 44 cases of dengue fever, the highest in the district, according to the centre.

For the entire district, a total of 272 people contracted dengue fever during the same period, the highest number of any district in the city. (Binh Tan District's population density is 11,718 per kilometre in 2011).

The lowest number of dengue fever cases was in Can Gio District, with a population density of 100 per kilometre. It had only 10 cases from January to May.

Besides Binh Tan, other districts with high population density and incomplete infrastructure include District 8 and districts Thu Duc, Tan Phu and Binh Chanh. They are all listed as high-risk areas for dengue fever.

Infographic on dengue fever in HCM City.

Phan Trong Lan, head of the city's Pasteur Institute, said that residents who had moved from other provinces were more susceptible to the dengue fever strains common to HCM City, which differ from the other strains in other parts of the country.

Thus, the residents have not built up immunity against the strains more common in HCM City. (There are four dengue fever strains, and the second incidence of dengue fever in an individual who has had the disease before can be more severe, if the strain is different from the first).

Lan said that more and more adults aged 15 and above in the city were contracting dengue fever.

The Preventive Medicine Centre showed that the rate of adult dengue-fever cases in the city had increased from 12.14 per cent in 1997 to 28.27 per cent in 2002.

Three studies in Asia using surveillance data showed that the rate was increasing in those areas as well.

In Singapore, for example, surveillance data showed the median age had shifted from 14 years in 1973 to 27 years in 1996, according to a study on re-emerging infectious diseases, conducted by Singapore's National Ministry of the Environment's Quarantine and Epidemiology Department.

Surveillance data from 1975 to 1984 also showed an increase among adults in Jakarta and other provinces in Indonesia.

Prevention

"Mosquito vector control by spraying chemicals and clearing out water containers is the best dengue fever prevention for now," Lan added.

Households should spend 10 minutes each spring to clear out water containers, he added.

Truong Thi Tuyen, head of the Health Prevention Division at Thu Duc District's peri-urban Linh Xuan Ward, said the high-risk areas in the ward were sprayed twice a month, and once a month in other parts of the ward.

Disease-prevention activities have been carried out in wards, but only a few of the residents have attended, she said.

Moreover, migrants move more often, making it more difficult to educate people about prevention and limit disease outbreaks.

Tuyen said Linh Xuan Ward had 43 dengue fever cases for the first five months of the year, an increase of seven compared to the same period last year.

High mobility and crowded living conditions were partly to blame for disease transmission.

Thu Duc District's Preventive Medicine Centre said that the number of measles (31) as well as hand, foot and mouth cases (15) was high for the first five months of the year.

A study by the East West Center based in Honolulu, Hawaii, which analysed the H5N1 outbreaks of 2004 and 2005 in Viet Nam, showed that peri-urban areas had a 40 per cent higher chance of outbreaks compared to rural areas and 14 per cent compared to urban areas.

Poultry density, flock-size diversity (small and large flocks of animals in one area) and land-use diversity (agricultural land and built-up land areas of equal proportion) were found to be high in these areas, the study said.

VNS/VNN