Test numbers fall but positivity rate higher

In the week before the enforcement of the strict lockdown on April 14, Chattogram's rate of infection was hovering around 12 percent to 20 percent. But in the days since then, the rate has jumped up.

However, although the rate of infection has increased, the gross number of positive cases has decreased this week, creating confusion in city dwellers as to whether the pandemic's severity is intensifying or diminishing.

But experts say it's neither. According to them, the situation this week is almost the same as the previous week. The numerical dilemma is caused by some other factors, they say, such as fewer number of people getting tested.

For example, one of the things that changed this week is that patients with mild symptoms have stopped coming for testing due to the unavailability of public vehicles, experts said. Only those who are quite certain of their symptoms are coming to medical facilities for testing.

On the other hand, sample testing of international returnees has decreased due to the shutdown of regular international flights. Back when flights were running, all inbound passengers were being tested upon landing, which meant more tests and more negative cases.

Yesterday, 347 positive cases detected out of 1556 samples, at a positivity rate of 22.3 percent. On Monday, 293 people tested positive out of 1,138 samples, putting the rate of positivity at 25.74 percent. On Sunday, 252 cases were detected out of 958 samples, putting positivity rate at 26.3 percent. 

Though the situation was apparently better before the hard lockdown, the number of samples tested was higher as well.

For example, on April 14, 417 positive cases were detected out of 2,682 samples, putting the positivity rate at 15.5 percent. On April 13, this was 431 cases out 2,621 samples, and on April 12, this was 541 cases out of 2,603 samples, putting positivity rates at 16.4 percent and 20.1 percent respectively.

"One of the reasons (for the higher positivity rates) is that we are testing fewer number of samples in the strict lockdown," said public health expert and head of Bangladesh Institute of Tropical and Infectious Diseases (BITID) Laboratory Prof Dr Shakeel Ahmed.  Additionally, "Many patients who have milder symptoms are choosing not to come for testing; only those with severe symptoms are taking the hassle," he said.

"This is why the rate of infection has increased compared to samples tested. Because if you test more symptomatic patients, the rate of infection will increase."

Citing the expatriates' situation, Dr Shakeel said, "Earlier, if we tested 1,000 samples in our laboratory, around 800 of them were of expatriates. Hardly 40 people out of those 800 tested positive, but around 60 out of the other 200 samples of common people came out positive."

For instance, on Sunday, a total of 428 samples were tested in BITID. Of those, 61 positive cases were detected. Of the 428 samples, a total of 105 samples were of the passengers of international flights. Of the 105 samples, only two positive cases were detected, said Prof Dr Shakeel Ahmed.

"All of this shows that the rate of positivity actually hasn't increased after the hard lockdown," he said.

"Our task now is to trace out those who maybe infected but are not coming for testing."

Echoing the same, Dr Abdur Rob, senior consultant of medicine and head of Covid-19 ward of Chattogram General Hospital, said although the rate of cases has increased this week, the actual number of cases has decreased.

"Unless we follow health guidelines, the rate or case of will not decrease," he stressed.

Chattogram Civil Surgeon Dr Sheikh Fazle Rabbi also said people in the city are still quite indifferent to health guidelines, but there is no alternative to maintaining it in order to improve the situation.