Health officials in West Africa say 25 more people have died from Ebola since 3 July, taking the total number of deaths to 518.
The World Health Organization (WHO) said 50 new cases of the deadly disease had also been reported.
A WHO spokesman said health workers were struggling to contain the outbreak in Sierra Leone, Liberia and Guinea.
Ghana's health ministry has confirmed that tests on a US citizen showed he did not have the disease.
The man had recently visited Sierra Leone and Guinea and was quarantined after showing signs of the virus.
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