Six children in the same Kampala family have contracted Ebola, authorities in Uganda's capital say, APA reports citing BBC.
For weeks medics have been calling for tougher measures to prevent the virus spreading to Kampala.
Viruses can spread faster in densely populated areas and this particular strain of Ebola - called the Sudan strain - has no vaccine yet.
Earlier this month the districts at the epicentre of this outbreak, Mubende and Kassanda, were put under quarantine.
The six siblings got infected after a relative came to stay from one of the country's worst-affected districts, and later died, health authorities confirm.
Since the outbreak began in September, Uganda's health ministry has recorded 109 cases and 30 deaths. As of Monday, 15 of those deaths were in Kampala.
Some fear that President Yoweri Museveni was too slow to act on early warnings from health workers about the viral haemorrhagic fever.
Health Minister Jane Ruth Aceng says she is increasingly concerned about transmission of the virus in urban areas, where the population is highly mobile.
The six siblings who tested positive for Ebola in the capital have not been named or had their ages revealed, to protect their identities. But we do know that the schools these children attend have not been closed.
Dr Aceng says six health workers who became infected after treating patients are also among those who recently died.
Kampala is the country's economic hub and if Ebola spreads fast there, there is a greater risk of the virus spreading to other countries.