The transmission of viruses after a transfusion therapy is usually due to the presence of the infective agent in the circulation of the donor.

In the past 30 years, the risk of transmitting a virus infection with transfusion has greatly decreased because of the development of microbiological research and new detection techniques (serological and nucleic acid testing (NAT)). At the same time, more restrictive donor selection criteria and pathogen reduction or inactivation technologies are usually employed to further reduce the risk of infection [10]. Residual risk is due to asymptomatic donors who donate in the “window period.”

Table 7.2 summarizes information related to the principal virus infections potentially transmitted by transfusion.

Bacteria infections following transfusion (Table 7.3) are often derived from microbial flora present on donor skin which contaminate blood products. They can also be due to systemic bacterial infections, though this is a rare event. From 2008, the Italian National Blood Center recommends using the first 40 ml of collected blood for testing, diverting it in tubes during withdrawal.

Regarding the kind of blood components, platelet concentrates are more frequently involved in IARTs, because their storage is at room temperature (22 ± 2 °C). However, medical and nursing staff must inspect the blood component before administration to check for integrity of bags, hemolysis, change in color, gas formation, and clots. Any of these findings must be communicated to the transfusion center to which the product must be returned.

The transmission of protozoa after transfusion is unequivocally due to the presence of the agent in the circulating blood of the donor. Sometimes it is not easy to identify infective donors, because some of these protozoa give no symptoms for years. In Italy, donor selection criteria specify a period of deferral for individuals who were born or visited endemic areas. The main problem with protozoan infections is the globalization in tourism and immigration from countries in which infection is endemic (Table 7.4).

In the past years, numerous emerging infections have been described in different areas of the world. Because of globalization of travel and immigration, it is a challenge for transfusion centers in the prevention of emerging IARTs [18].

The variant of Creutzfeldt–Jakob Disease (vCJD) is transmissible spongiform encephalopathy. Like the primitive CJD, it results from the changing of a prion protein into a protease-resistant form (PrP Sc). Originally, bovine spongiform encephalopathy affected cattle. The use of animal protein in bovine feed diffused the disease in cows. Successively, meat consumption by humans was responsible for the variant of Creutzfeldt–Jakob Disease, which has an earlier onset with neurological manifestations, dementia, and death in 7–38 months. At present, there are no invasive tests available for donors or patients and diagnosis is mainly confirmed postmortem. The policy for blood collection consists in deferring donors who lived in the UK (the area of first onset of the disease) from 1980 to 1992 and donors who present neurological diseases [19].

Severe Acute Respiratory Syndrome (SARS) is a recent disease emerged explosively in Asia in 2004. The coronavirus agent can cause pneumonia with rapid onset and is often fatal. The transmission by transfusion is not clearly detected, but it can be possible in the asymptomatic viral phase. Quarantine and traveler surveillance is employed in airports during the endemic period.

Middle East Respiratory Syndrome (MERS) is due to another coronavirus identified in Saudi Arabia in 2012. The virus can affect many types of animals, but recently dromedaries seem to be the most important source of infection for humans. Actually interhuman transmission is not demonstrated. Most infected patients report a severe respiratory disease with acute renal failure and high fatal rates [20]. As during SARS pandemia, travelers’ surveillance in airports is important in the endemic periods.

Xenotropic murine leukemia virus-related virus (XMRV) is a recent discovery and reported in uncertain association with chronic fatigue syndrome (CFS). This disease can potentially be transmitted by transfusion, but more extensive studies are needed to define the pathology [21].

Medical doctors when faced with an infectious disease in a hospitalized patient should always collect an accurate clinical history that must include transfusion of blood components and take into consideration that the viral/bacterial/protozoan infection could be related to a transfusion event. If a transfusion-transmitted infection is suspected, the clinician must contact the transfusion center that will provide a look-back of the blood products and a follow-up of the involved donors.