Emerging infections are unpredictable. EID rarely stands out as unusual, and the continuous pressure on health care budgets forces clinicians and laboratories to prioritize their diagnostic work-up to common and treatable conditions. Emerging infections can be caused by
• Previously undetected or unknown infectious agents
• Known agents that have spread to new geographic locations or new populations
• Previously known agents whose role in specific diseases has previously gone unrecognized.
• Re-emergence of agents whose incidence of disease had significantly declined in the past, but whose incidence of disease has reappeared. This class of diseases is known as re-emerging infectious diseases