Another person has tested positive for the radioactive substance which killed a former Russian spy.
Scotland Yard is investigating Alexander Litvinenko's murder
The Health Protection Agency (HPA) said the test had been carried out on a guest at The Pine Bar at the Millennium Hotel in London's Mayfair.
Alexander Litvinenko drank there with associates on the day he is believed to have been poisoned, 1 November.
The number of people affected by polonium-210 who are facing slight health risks now stands at 16.
Mr Litvinenko, 43, visited a number of sites in the capital on 1 November, including several hotels, an Italian restaurant in Mayfair and the Itsu sushi bar in Piccadilly.
Last week the HPA revealed two more people had tested positive for the radioactive substance, one of whom had also visited The Pine Bar.
The HPA said the 16 who have tested positive for higher levels are not expected to fall ill in the short term but do have a greater risk of developing cancer in the long term.
A spokeswoman for the HPA has said they are just 0.05% more likely to develop the disease than any other member of the public.
The latest update from the HPA says traces of polonium-210 have been found in the urine of 679 people.
Of those, 560 had results of less than 30 millibecquerels (mBq) per day, which is "below reporting levels".
Levels of up to 15 mBq can be found in the urine naturally.
A total of 119 people had "probable contact" with polonium-210 but with "no health concern to the individual".
Father-of-two Mr Litvinenko died at London's University College Hospital on 23 November and Scotland Yard are currently investigating his murder.