Because of a simultaneous outbreak of another disease, the extent of the Zairian Ebola epidemic may have been slightly overestimated, physicians working with Doctors Without Borders said yesterday.

The doctors with the Brussels-based independent relief group said that the other disease is caused by shigella bacteria. Both the bacteria and the Ebola virus cause bloody diarrhea, so some shigella cases were misdiagnosed as Ebola.

The physicians were back in Brussels after working in Kikwit, where both epidemics began. Of the 172 reported cases of illness in that city, 50 Ebola cases have been confirmed, with 29 deaths, they said.