Work stations contain nearly 400 times as many microbes than lavatories, it is claimed.
Office equipment should be regularly disinfected to prevent the spread of viruses and bacteria responsible for disease.
The reality of our grubby working environments is exposed in a study by the University of Arizona.
A desk is capable of supporting 10 million microbes and the average office contains 20,961 microbes per square inch, according to research.The key offenders are telephones, which harbour up to 25,127 microbes per square inch, keyboards 3,295 and computer mice 1,676.
By contrast, the average toilet seat contains 49 microbes per square inch, the survey showed.
Microbiologist Dr Charles Gerba, of the University of Arizona, who carried out the research, said: "When someone is infected with a cold or flu bug the surfaces they touch during the day become germ transfer points because some cold and flu viruses can survive on surfaces for up to 72 hours.
"An office can become an incubator."