The discovery has led to the roll-out of a "surge testing" programme.
It comes as the number of patients with Covid-19 in hospital has reached a record high in England.
Two men and a woman in their 20s died on road close to Heathrow Airport.
A reading of 34C was taken by the Met Office at Heathrow and in west London.
Victim was taken to hospital but was later pronounced dead.
The quake happened in the early hours, and follows a series of similar incidents in Surrey in February.
Four other people taken to hospital.
It is believed the woman and her alleged killer knew each other.