Heathrow welcomed 5.4 million passengers in February, down 4.8 per cent on last year after adjusting for the extra leap day.
The fall was largely due to lower demand on Asian and European routes in the wake of the coronavirus outbreak.
Demand has continued to weaken going into March, Heathrow officials said, with a further year-on-year decrease expected in coming weeks.
Heathrow chief executive, John Holland-Kaye, said: “The threat of coronavirus is an increasing challenge for the UK, and we are working day and night to ensure Britain’s front door is open and safe for our people and passengers.
“We will continue to work with the government to limit the impacts this will have on UK plc.”
Regular deep cleaning has been introduced across all Heathrow terminals as well as increased availability and provision of hand sanitisers.
A dedicated Public Health England team remains in place at the airport, implementing clinically-informed, evidence-driven processes to support passengers showing symptoms of the virus.
Current processes include an early warning system allowing airline crew to report any illness on board flights ahead of landing.
In February, the airport saw over 115,800 metric tonnes of cargo pass through its doors, down 9.5 per cent, as the effect of coronavirus was felt on global trade.