In more recent years, some emerging infectious diseases (EID) have been identified as potential threats to blood safety and required rapid responses, with particular mention to some arboviruses. Due to sustained globalisation and climate change, continued vigilance and horizon scanning for newly emerging or re-emerging infectious pathogens have become essential tools as regards to the microbiological safety of the blood supply. The classical attributes of a transfusion transmission threat include: 
- An asymptomatic period of infection during which the agent is present in the blood
- The agent is transmissible by the intravenous route
- It causes symptomatic disease in some or all recipients
- It is resistant to blood processing and storage conditions. 
Table 1 from Perkins et al (43) compares the features of established and EID of concern for blood safety. The new paradigm includes a wide array of agents that do not fit the classical model; instead, potential blood-borne infectious agents initially presenting in any region of the world can overcome the barriers of geographical restriction through rapid population movements.  
In 2009 the Transfusion Transmitted Diseases Committee of the AABB) put together a list of agents that are known or have the potential to be transfusion-transmitted (55). Each agent was assigned a priority risk level under three different categories:
- Scientific/epidemiologic evidence regarding blood safety
- Public perception and/or regulatory concern regarding blood safety
- Public concern regarding the disease agent
The initial list includes 68 agents, among them human variant Creutzfeldt-Jakob disease, dengue viruses, Babesia, Chikungunya virus, St Louis encephalitis virus, Leishmania, Trypanosoma cruzi, Chronic wasting disease, HHV8, human parvovirus B19, influenza A virus, subtype H5N1, simian foamy virus, Borrelia burgdorferi, hepatitis A virus (HAV), hepatitis E virus (HEV), Anaplasma phagocytophilum. Since then, the number has grown to 77 agents (56). It must be remembered that although most infectious agents have world-wide relevance, the assessment and classification was made with focus towards the USA and Canada.
A) Surveillance and vigilance: To safeguard the microbiological safety of blood supplies, blood systems must ensure:
1. Continued collection of donor and recipient data, including outcomes, to inform safety policy  
2. Recognition of a transfusion-transmission threat, methods for quantitative risk assessments and the appropriate management of such threats
3. As regards specifically EID, methods to monitor agent (re)emergence and assessment of risk based on local parameters, including donor and recipient population
4. Mechanisms must exist to allow surveillance, threat assessments, triggers for action, and as needed, intervention development, implementation and assessment of
B) Response from transfusing facilities and blood establishments to possible TTI 
1. The clinician responsible for the recipient must appropriately consider transmission of infection in association with transfusion.  Specialist opinion should be sought at an early stage.
2. There must be a formal reporting mechanism to the responsible blood organization with standardized minimum data set of information
3. Evidence of infection that triggered reporting must be carefully verified and appropriate samples from recipient(s) must be retained for investigation
4. Archive donation storage must be in place
5. Advice/oversight by a specialist in transfusion microbiology, with access to required tests. Determination of imputability may require specialist tests, which may include molecular-based techniques performed in referral centres 
6. Production of report following each reported potential TTI with outcome and conclusion, which must include duty of care to the donor, when donor infection is confirmed. Appropriate feedback is important.