The slow pace of testing for COVID-19 infection in Ontario is raising concern among experts that the province is falling short of capturing the true spread of the coronavirus, and causing anxiety among people waiting days for test results.

The latest figures posted by the province's Ministry of Health show nearly 4,000 people who have been tested for COVID-19 are awaiting their results, while Public Health Ontario says the turnaround time at its laboratory has risen to four days.

However, CBC News has spoken with multiple patients who have waited longer than four days for their results. Last month, the Public Health Ontario laboratory was providing test results in 24 hours.

Michael Gardam, an infectious disease specialist and medical chief of staff at Humber River Hospital in Toronto, said Thursday the lag for results is now actually five to seven days.

This means the new infection numbers being reported each day actually represent the spread of the virus several days ago, raising questions about the actual current rate of transmission.

After two days of relatively small increases in the number of new cases, Ontario announced 43 new positive tests Thursday morning, a 20 per cent increase in the total number of cases overnight.

Health Minister Christine Elliott called the current lengthy wait for coronavirus test results 'not acceptable' during a news conference Wednesday, but could not say how long it will take to reduce the wait time. (Tijana Martin/Canadian Press)

The number of cases described as "under investigation" — people who have been tested but whose results are not yet available, has hit 3,972, the highest backlog Ontario has seen so far in the COVID-19 pandemic.

"Now that some of the large hospital labs are up online in terms of doing testing, I think we'll get through some of that backlog, so hopefully this will improve over the next week or so." Gardam said Thursday on CBC Radio's Metro Morning.

In the past week, the province announced roughly 900 to 1,000 results per day. On Thursday, there was a sharp jump, showing a total of 2,161 new results. The province is aiming to reach the lab capacity to process 5,000 tests daily, but various health officials have been unble to put a timeline on when that target will be achieved.

Health Minister Christine Elliott called the current lengthy wait for test results "not acceptable" Wednesday, but could not give a time frame for when the wait time will be reduced.

"We are working on doing much better than that and I anticipate that we will be caught up very shortly with the lab tests," Elliott said at a news conference.

"The numbers [of samples to be tested] that are going to the lab are going up quite quickly," said Barbara Yaffe, Ontario's associate chief medical officer of health.

"The good news is the lab capacity is going up," Yaffe told a news conference Wednesday. "The Public Health Ontario lab itself has increased its capacity to test, and we have a number of hospital labs coming on that will eventually increase our capacity to 5,000 tests a day."