A royal spokesman confirmed that that the person, whose identity is not known, tested positive for the virus while Her Majesty, 93, was still at her London residence.
Queen Elizabeth was whisked away to Windsor Castle last Thursday soon after the diagnosis of the royal worker, and royal sources say she remains in good health and good spirits.
The aide fell ill and tested positive for the virus earlier last week, but it is not known if the worker served the Queen closely.
Every member of Royal Household staff who worked with the affected staff member has since been placed in self-isolation and Buckingham Palace is now closed to tourists and non-essential workers.