The phrase "mysterious outbreak" refers to a situation where an illness or disease is spreading among people, but its cause and characteristics are not fully understood or known at the time. Full definition
The realization that trace amounts of arsenic might pose a health threat began with mysterious outbreaks of disease in Southeast Asia. (discovermagazine.com)
Building rapport also encourages scientists from other countries to be open with those in the United States about mysterious outbreaks on their soil, despite the potential harm this could cause to their economy, says Hotez. (scientificamerican.com)
Noting mysterious outbreaks such as SARS, Legionnaires Disease, and the cruise ship malady, Norwalk Virus, a reasonable person would begin to question everything we thought we knew about vaccines. (thedogplace.org)