GENEVA/LONDON — The head of the World Health Organization on Tuesday urged countries to maintain surveillance of coronavirus infections, saying the world was blind to how the virus is spreading because of falling testing rates.

As many countries reduce testing, WHO is receiving less and less information about transmission and sequencing, Director-General Tedros Adhanom Ghebreyesus told a news conference at the U.N. agencys headquarters in Geneva.

This makes us increasingly blind to patterns of transmission and evolution.

Bill Rodriguez, chief executive of FIND, a global aid group working with WHO on expanding access to testing, said testing rates have plummeted by 70 to 90%.

We have an unprecedented ability to know what is happening. And yet today, because testing has been the first casualty of a global decision to let down our guard, we are becoming blind to what is happening with this virus, he said.