Reactions due to bacterial pyrogens and bacteria

The presence of bacteria in transfused blood may lead either to febrile reactions in the recipient (due to pyrogens) or to the far more serious manifestations of septic or endotoxic shock. Bacterial-transmitted infections are considerably more frequent than serious acute manifestations of virus-transmitted infections in countries such as the UK (see p. 255).

Bacterial pyrogens are rarely the cause of reactions with present-day methods of manufacture and the sterilization of fluids and disposable equipment. Infection of stored blood is also extremely rare, but has a very high mortality in recipients. Skin contaminants are sometimes present in freshly donated blood but many (e.g. staphylococci) do not survive storage at 4°C. However, they will grow profusely in platelet concentrates stored at 22°C. A number of Gram-negative psychrophilic, endotoxin-producing contaminants found readily in dirt, soil and faeces (pseudomonads, coliforms) may very rarely enter a unit and grow readily under the storage conditions of blood (and even more rapidly at room temperature).

Healthy individuals who are bacteraemic at the time of donation may also act as a source of infection. The majority of such cases relate to transmission of Yersinia enterocolitica, which grows well in red cell components due to its dependence on citrate and iron.

Transfusion of heavily contaminated blood will usually lead to sudden, dramatic symptoms, with collapse, high fever, shock and DIC with haemorrhagic phenomena. These symptoms resemble, and may be more severe than, those of ABO incompatibility. Prompt recognition of the cause and administration of broad-spectrum intravenous antibiotics, in conjunction with the treatment of shock, are vital. The diagnosis should be confirmed by direct microscopic examination of the blood, and blood cultures from the recipient and the blood bag.

Prevention of this potentially disastrous complication of blood transfusion rests on stringent observation of procedures for aseptic techniques in blood collection and in the manufacture of anticoagulant solutions and packs. Packs should never be opened for sampling, and the unit should be transfused within 24 h if any open method of preparation has been used (for example, washed red cells, frozen-thawed blood). Blood should always be kept in accurately controlled refrigerators (with alarms), maintained strictly at 2-6°C, and a unit of blood should never be removed and taken to the ward or theatre until it is required. The practice of obtaining multiple units of blood for the same patient, and leaving unused units at room temperature (or in uncontrolled ward refrigerators) until needed must not be tolerated. Bacteria may cause haemolysis or clotting of blood and all units should be inspected for these before transfusion. Platelets should be inspected for discoloration, foaming and absence of swirling.

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