A mysterious illness has Texas health officials worried after half of those infected died from the unidentified disease, the ABC News reported Wednesday. The Montgomery County Health Department said eight patients had presented with flu-like symptoms or pneumonia-like symptoms. Of the eight infected, four have died. Despite their symptoms, none have yet tested positive for the flu, officials said in a statement. The patients range in age from 41 to 68 and it was unclear if any had underlying health issues that could have adversely affected their health.