Characteristics of microorganisms most likely to cause a global pandemic

A potential global catastrophic risk-level pandemic pathogen will most likely have a respiratory mode of transmission; be contagious during the incubation period, prior to symptom development, or when infected individuals show only mild symptoms; and need specific host population factors (e.g., immunologically naïve persons) and additional intrinsic microbial pathogenicity characteristics (e.g., a low but significant case fatality rate) that together substantially increase disease spread and infection. RNA viruses are the biggest threat.