Number of Positive Covid-19 Cases: All of reality may not be reflected

The worry stems from the disparity in the number of positive cases found at the testing lab at the capital's Bangabandhu Sheikh Mujib Medical University and 15 others elsewhere.

Equipped with a skilled manpower, the BSMMU lab goes through a rigorous background check before carrying out any test. And the result is a higher percentage of positive cases.

The situation at the other labs is not the same. The number of negative cases remains high there, giving what may be a false impression that coronavirus infection has been low in certain areas, said the experts.

Between January 28 and March 26, the government's disease control agency -- Institute of Epidemiology, Disease Control and Research (IEDCR) -- tested samples from 920 people, and the rate of positive cases was 4.8 percent (44 tested positive).

After March 27, the Directorate General of Health Services (DGHS) expanded the testing facilities to 16 labs across the country, apart from the one at the IEDCR.

Till yesterday, the authorities tested 14,868 samples in total and confirmed 1,231 positive cases across the country, which means 8.2 percent of the samples are positive.

But for the first 9,562 tests in the United States, the rate was 22.9 percent, according to covidtracking.com. Collectively, the rate was 19.6 percent out of 28,05,892 tests in the US as of Sunday.

Of the other countries severely hit by the pandemic, Iran carried out the Covid-19 tests most extensively. Its tally of positive cases currently stands at over 64,000, which is 31 percent of the 200,000 tests it conducted, according to www.worldometers.info.

In Belgium, around 26 percent of all who were tested turned out to be infected. France conducted over 200,000 tests as of April 2, and it had 59,000 confirmed cases, which is 26.4 percent of all the tests.

For India and Pakistan, the rate of positive cases for the first 10,000 tests could not be known.

However, it was 4.67 percent (7,703) of 1,64,773 people tested in India as of Saturday, according Indian Council of Medical Research. In Pakistan, the rate was 8.3 percent (4,788) of 57836 people tested as of Friday, according to Pakistan government data.

Like most countries across the world, the authorities in Bangladesh are using the PCR technique, a gold-standard technology for Covid-19 confirmation, which detects pieces of the coronavirus through analysing sputum or mucus samples collected from the human body -- nasal and throat.

Talking to The Daily Star on Sunday, Prof Nazrul Islam, a noted virologist and former vice chancellor at the BSMMU, said the high number of positive cases detected at the lab there "reflects there might be some issues in case selection at the other labs".

"If samples are not collected from the actual suspected patients, test results will be negative," he said, warning that in the absence of proper detection, many Covid-19 patients might not be diagnosed and spread the virus to others.

Several other experts echoed his views.

Although the lab-or-region-wise rate of positive cases is uncertain, The Daily Star analysed data on positive cases found at different labs.

From April 1 to 12, the BSMMU lab detected 136 positive cases from 369 samples. It means around 34 percent of all the samples tested positive. This rate was higher than those of all the other 15 labs combined, shows DGHS data.

Take another example.

On Thursday, the authorities reported 62 new cases in Dhaka city. The BSMMU tested 59 samples and found 40 to be positive. The eight other labs in the city detected the other 22 positive cases.

With more than 80 identified infected areas, the city so far accounts for almost half the Covid-19 cases detected across the country. But the percentage of positive cases at different labs provides a confusing picture about the transmission level, said experts.

On March 25, the Institute of Public Health (IPH) in Dhaka tested 650 samples and found only seven Covid-19 cases. In Chattogram, the Bangladesh Institute of Tropical and Infectious Diseases (BITID) tested 89 individuals' samples in 24 hours till Friday afternoon and detected just three positive cases, records show.

THE REASONS?

According to WHO interim guidance for Covid-19 tests, a number of factors could lead to a negative result in an infected individual.

Those include: poor quality of the specimen, containing little patient material, the specimen was collected late or very early in the infection, the specimen was not handled, shipped appropriately, and technical reasons inherent in the test.

So, the sample collection requires trained hands to collect high-quality sputum or nasopharyngeal swabs, located at the back of the nose that meets the top of the throat containing sufficient amounts of viral RNA.

The amount of the viral RNA in the sample can vary within the same patient depending on the timing of the test, according to different scientific papers.

Moreover, different types of specimen show different percentage of positive result: bronchoalveolar lavage fluid shows 93 percent positivity, fibro bronchoscope brush biopsy 46 percent, sputum 72 percent, nasal swabs 63 percent, pharyngeal swabs 32 percent, faeces 29 percent, blood 1 percent and urine zero percent, according to Journal of American Medical Association.

Currently, all but the BSMMU lab collect nasal and throat swabs for the test, according to officials.

The BSMMU lab collects sputum samples, source said.

Case selection is done mainly in two ways -- from symptomatic patients coming to hospitals, and responding to calls to the given hotline numbers.

Besides, Covid-19 hotspots usually get more importance in sample collection, the sources said.

Medical technologists and other staffers at every upazila are currently collecting samples, after they were trained up online last month, according to the DGHS.

Besides, the IEDCR has its own team for sample collection.

"Another problem is that our sample collectors [often fail to collect] quality samples. Maybe they are not putting the swab stick as deeper as required," Prof Moudud Hossain, an expert assigned to advise the government on Covid-19 control and prevention activities in Rangpur division, told The Daily Star on Saturday.

He said positive cases can go undetected if samples are not collected properly. "It makes us worried."

In a daily briefing last week, Prof Abul Kalam Azad, director general of the DGHS, also admitted that many of those collecting the samples lacked the skill.

Other than these reasons, Prof Saif Ullah Munshi, chairman of virology at BSMMU, focused on the case selection procedure.

"But even if sample collection procedure is done correctly, the swab may produce a false negative because the virus passes from the upper to the lower respiratory system as the disease develops step by step," he said.

Any Covid-19-like symptoms could be categorised into three types -- suggestive, suspected, and confirmed case.

Prof Munshi said, "Our trained clinicians find out the suspected cases based on detailed history and symptoms. If we would consider the suggestive cases, we would get more negative cases. But it would be the waste of resource."

He thinks the entire testing activity needs to be brought under a uniformed mechanism.

"Otherwise, tests results will not reflect the real situation," he added.

IN DARK, IN DANGER

Experts said if the real situation of the coronavirus transmission is not acknowledged, the ongoing shutdown might be futile.

"The transmission of the virus is ongoing. Here, case identification is important if we want to make the lockdown effective," Prof Mushtuq Hussain, consultant at the IEDCR, told The Daily Star.

Prof Nazrul Islam said, "There has been havoc in Narayanganj. But we do not know how many samples they have collected from there … There is no consistency between the test data and what they say.

"How much value could the data have if the procedures were wrong?"