Jakarta. Tangerang, a city in Banten province with two million inhabitants on the outskirts of Jakarta, has found that the real number of Covid-19 cases among its population might be about 50 times higher than the official figures after completing an epidemiological study last month. 

The study concluded that the novel coronavirus had infected about 2.43 percent of residents in Tangerang. That percentage translates to around 53,100 people, as the city has a population of 2.19 million people, according to the Central Statistics Agency's latest available data. 

Mayor Arief Wismansyah said in a statement on Monday that the city's health department and the University of Indonesia's school of public health conducted the study on a random sample of 3,000 people. The study participants took serology tests that detected particular antibodies in one's blood. The antibodies' presence indicated they might have exposed to the coronavirus sometime in the past.

The study used a two-stage stratified sampling method and reported a 95 percent confidence interval of between 1.9 percent to 3 percent. That means the actual number of people exposed to Covid-19 may lie somewhere between 41,500 to 65,500. 

In comparison, Tangerang only confirmed a total of 1,071 cases as of Tuesday, with 57 deaths. Jakarta, Indonesia's current epicenter of the pandemic, reported on Tuesday a total of 56,175 people in the capital had had Covid-19, and 1,450 of them had died. 

Arief said the survey result had shown that the majority of the Covid-19 cases in the city have gone undetected with the majority of the infected people who did not show any symptom. Often, asymptomatic family members carried the coronavirus into their home and infected other family members, Arief said.

"That's why we tightened the restriction again so that the number [of new cases] would decline," Arief said in the statement. 

Under the latest round of restrictions, called PSBL, the city imposes lockdowns at the urban hamlet (RW) level. People's movements between urban hamlet in red zones — those with a spiking number of new cases — are heavily restricted.

Arie said the city's first PSBL in June managed to reduce the number of hamlets in red zones by 50 percent in two weeks. 

The city opted for the smaller scale restriction as it finds most of the Covid-19 cases in the city came from family clusters, Arief said.

Arief said the city administration had listed the help from the National Police and the Indonesian Military to deploy their personnel for enforcing the restrictions in urban wards. 

More Testing, Please

Tangerang data was the latest piece of evidence that the country's weak tracing and testing regimes have allowed most of the asymptotic cases to roam free undetected and spread the coronavirus to more unsuspecting people.

"The result of the Tangerang study was not too surprising. That means that we have must increase our tracing and testing capacity soon," Tri Yunis Miko Wahyono, the head of the epidemiology division at the University of Indonesia's school of public health, told the Jakarta Globe on Tuesday. Miko did not involve directly in the Tangerang study, which was conducted on 11 to 19 August. 

Indonesia tested more than 42,000 samples using the polymerase chain reaction (PCR) test on Tuesday, the country's record high since the pandemic began, but used only half of the tests on suspects. 

The World Health Organization (WHO) had urged for several months now that Indonesia must test at least one suspect for every 1,000 population per week — or about 38,700 tests per day — to be able to gauge the spread of the pandemic within its territory properly. WHO said in its latest situation report last week that only Jakarta, Yogyakarta, and West Sumatra were able to meet that criterion. 

Miko said the school was preparing several studies to complement Indonesia's pandemic data. "A similar study had been carried out in Bali, even before the one in Tangerang. But we haven't published it yet," Miko said.

"Soon, we will hold surveys for Jakarta and Indonesia," he said.