A yet-to-be-released survey carried out by the health directorate gives a worrying picture of the spread of Aedes mosquito -- carrier of the virus responsible for dengue fever -- in Dhaka city.

The survey, conducted on 3,150 houses in 98 wards of the two city corporations between June 18 and 27, has found presence of Aedes mosquito larvae in 20 percent of houses under the Dhaka North City Corporation and 15 percent of houses under the Dhaka South City Corporation.

The larvae of Aedes mosquito were found in 549 of the total houses surveyed. Of them, over 43 percent are multi-storeyed apartment buildings and 21.41 percent are houses, according to the survey of the Directorate General of Health Services (DGHS).

"This is a matter of concern. The authorities concerned should immediately identify the breeding grounds and conduct drives," entomologist Kabirul Bashar of Jahangirnagar University told The Daily Star.

The survey comes at a time when deaths from dengue have been reported almost every day since June.

In the last 24 hours, four dengue patients died and 436 others were hospitalised, according to the DGHS.

Till yesterday morning this year, the total number of deaths in dengue rose to 56 while the total number of cases jumped to 9,193.

Of the total deaths, 34 people died in June.

According to a DGHS analysis on 50 dengue deaths, 62 percent of them are female and 38 percent are male. The age group that saw the highest -- 60.80 percent -- number of deaths is between 19 and 50 years.

The DGHS analysis has also found that 80 percent of the deaths happened within three days after the patients were admitted to a hospital.

Stagnant water collected in any container or place is the breeding ground for Aedes mosquito.

Dr Md Ekramul Haque, deputy programme manager of malaria and ATD control programme at the DGHS, said the health directorate issued letters to all the hospitals across the country to take preparation for dengue management.

Referring to the survey, he said the Average Breteau Index (BI) was found to be over 20 in over 40 wards of the two city corporations, which means those wards are most at risk.

The BI is defined as the number of mosquito-positive containers found in every 100 houses inspected in a given area. The BI of an area over 20 means the area is at high risk of dengue infection.

Among the positive wet containers which are found in the houses, the highest 14.54 percent are found in buildings where stagnant water is collected due to rain or other reasons, 9.28 percent in plastic buckets and 8.73 percent in plastic drums, said Haque.

Putting stress on awareness building, entomologist Kabirul Bashar said the dwellers should play a vital role in destroying breeding sources of Aedes mosquito in their homes and adjoining places.

The authorities concerned should involve local people in conducting drives to eliminate Aedes breeding grounds, he said.

About the deaths from dengue, HM Nazmul Ahsan, associate professor at Shaheed Suhrawardy Medical College Hospital, said delayed admission is the main cause for the increasing number of deaths this year.

Citing an example of late admission, he said, "We received a critical patient on Sunday who was first admitted to a hospital in Savar before being shifted to another. When the condition of patients becomes critical, those hospital authorities send them to government hospitals."

Many private hospitals do not follow the national guidelines which are mandatory to treat dengue patients, Nazmul added.

Last year, the total number of dengue deaths was 281 while the total number of cases was 62,382, according to the DGHS.

Meanwhile, the DNCC yesterday cancelled leave of all the employees and officials, until further notice, who contribute directly to controlling spread of Aedes mosquito in their respective areas.

The DNCC mayor at a programme yesterday said leave of employees was cancelled so that dengue cannot spread to the whole city.

He also said people's awareness is very important as the Aedes mosquito breeds in clean water.

The DSCC will also start a three-day special operation in 25 of its wards. The drive will start from the Boldha Garden at 10:00am today.