Nine percent of the Dhaka city dwellers have already been infected with coronavirus and 78 percent of them had no symptoms, according to a study.
The first-ever cross-sectional study indicates that many undetected carriers have been spreading the deadly virus, experts said.
"The study proves the number of infected people is more than what we thought. The transmission is going on extensively in an unknown and uncontrolled way," Prof Ridwanur Rahman, an infectious disease specialist, told The Daily Star yesterday.
A total of 3,227 households were surveyed across the capital between April 18 and July 5, jointly by the Institute of Epidemiology, Disease Control and Research (IEDCR) and the International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b).
Of the households, five percent had one or more family members who had Covid-19 symptoms.
In these households, 211 individuals were found symptomatic and of them, 199 were tested with RT-PCR tests.
Of them, 30 percent were tested positive for Covid-19.
Meantime, 201 individuals from these symptomatic households were selected for RT-PCR tests and 14 percent of them tested positive.
On the contrary, 538 individuals from those households which had no symptomatic members were tested.
Of them, eight percent tested positive.
Additionally, 720 households in six slums in Dhaka city were also surveyed and six percent individuals under the study were found to be infected.
Overall, nine percent among all individuals in Dhaka city was estimated as RT-PCR positive, according to the preliminary study.
The authorities have not shared the study details yet.
"We will sit to discuss [the study outcome] soon and then we will plan the next step. We will inform you everything," Prof ABM Khurshid Alam, acting director general of the health directorate, told The Daily Star yesterday.
According to the health directorate testing data, the transmission of Covid-19 appeared to have stabilised across the country throughout the month of July.
However, from August 5, numbers of new patients seem to have an increasing trend.
In Dhaka city, around 1,000 new patients were being added to the daily tally. Between July 19 and 29, the total number of confirmed cases rose to 48,322 from 38,324, which is about a 10,000 rise in 10 days.
Yesterday, the number of confirmed cases in Dhaka reached 67,135, nearly a 19,000 rise in 13 days since July 29.
"We are observing that the confirmed cases are rising by more than 50 a day in at least 38 districts. In Dhaka and other big cities, this number is higher. It proves that the transmission has started to increase again after seven days of Eid-ul-Azha," Mushtuq Hussain, consultant of the IEDCR, told The Daily Star yesterday.
"The transmission may continue to increase in the days to come, I think," he added.
About the IEDCR's study, he said, "It can be assumed that people carrying the virus are everywhere. So, making sure masks are used is urgent, along with case detection and isolation."
Echoing him, Prof Ridwanur said, "The virus transmission will not stop by itself. Active intervention is a must."
During the last one month, the every day positivity rate has increased. Positivity rate is the percentage of infections of the people tested.
On July 5, the positivity rate was 19.57 percent which reached 25.23 percent on July 15 and has stayed over 20 percent since then.
Yesterday, this rate was 20.22 percent.
Experts said case detection and isolation was the key to control transmission and there was no alternative to antibody testing.
"It is not possible to bring all people under RT-PCR testing as it is costly and time- consuming. On the contrary, antibody tests can identify which people have developed antibodies within a minute. The government should permit the use of antibody test kits immediately," said Prof Ridwanur.
The immediate past DGHS DG Prof Abul Kalam Azad had also said they were planning to permit antibody testing.
The national technical advisory committee on Covid-19 also recommended antibody and the antigen-based rapid tests.
In yesterday's briefing, Prof Nasima Sultana, additional director general of the DGHS, said that more 33 Covid-19 patients died in the 24 hours until 8:30am.
With this, the death toll reached 3,471, around 1.32 percent of all the 2,63,503 confirmed cases.
Some 2,996 people of 14,820 tested were found infected during the same period.