Deep vein thrombosis (DVT) can be caused by infections, scientists have discovered.
Researchers from the London School of Hygiene and Tropical Medicine found a "causal relationship" existed between DVTs and respiratory and urinary infections, at its most dangerous during the first two weeks of infection.
Having analysed results from over three million patient records in the UK, it was found that the process of infection, rather than any specific kind of infection, was responsible for the increased risk.
"Our results show that in a community setting, acute infection is linked to a transient increase in the risk of venous thromboembolism - both DVT and PE [pulmonary embolism] - suggesting a role for acute infections in triggering such events," the study noted.
"We now need to uncover the mechanism that underlies the risk we propose."
Around 32,000 deaths occur each year when a clot builds up in the bloodstream before being dislodged and travelling to the lungs, where it can often lead to a fatal pulmonary embolism.
An all-party group on thrombosis was formed yesterday by Welsh MP John Smith, seeking to increase awareness of the symptoms that can precede a DVT attack.
More people die from DVT attacks in the UK than from breast cancer, road accidents and AIDS put together.