The province’s public health agency will launch a major study Friday to get a clearer picture of how many Ontarians have already had Influenza A (H1N1), also known as swine flu, and is recruiting 3,000 volunteers willing to give blood samples.

“It will give us a sense of how widespread H1N1 has been in Ontario,” explained Dr. Michael Gardam, director of infectious disease prevention at the Ontario Agency for Health Protection and Promotion.

About 4,000 Ontarians have tested positive for the swine flu virus through lab tests. But it’s believed this number is just the tip of the iceberg because most people with influenza symptoms do not visit a doctor.

Some people who have contracted H1N1 wouldn’t have even known it because they had no symptoms, said Mount Sinai microbiologist Dr. Allison McGeer.

The results will give public health officials an indication of how many people might get sick in the fall.