Further tests on the first reported case of anthrax outside the United States since the September 11th attacks have proved negative.
The Kenyan Minister for Health, Mr Sam Ongeri, last week said a letter sent to a Nairobi businessman from the US contained anthrax.
But after further testing and technical advice from the CDC (Center for Disease Control) and US embassy medical staff, the initial positive result has been reversed.
The Kenyan case was initially thought to be the first case of anthrax sent by post outside the United States.
Kenyan health ministry officials said they were not yet aware of the new findings, but said they continued to receive letters suspected of containing traces of the deadly disease in the form of white powder.
"We have received at least 53 suspected cases of anthrax by today," said Mr Charles Njuguna, a clinician with the Ministry of Health's Anthrax Secretariat.
"So far 43 have been tested and are negative, while the tests for the others are ongoing. There are a lot of hoaxes. Some people are taking advantage of the situation to scare their enemies," he added.
He said some letters were found to contain maize flour, salt or ground chalk, but the vast majority did not contain any powder at all.