Six people have so far died in what is suspected to be Ebola and Marburg viruses in Masaka district.
The strange illness broke out in the district five weeks ago.
On Wednesday, four patients from parishes of Kasaka and Mazinga in Buwunga Sub-county were admitted at Masaka Regional Referral Hospital with a similar illness.
They had advanced fever, intensive vomiting, passing bloody stool and yellow eyes, all signs of Ebola and Marburg fevers.
They were monitored at an isolation ward.
Two of the four passed away on Saturday.
Eleazer Mugisha, the Masaka hospital principal administrator, told Daily Monitor preliminary blood samples tested negative to Ebola, Marburg and Rift Valley fever which they had earlier suspected.
Mugisha said the remaining patients were responding well to drugs, explaining that the victims were brought in very critical condition.