Transfusions during ' severe ' bacterial ( tissue - invasive ) infections were associated with increased risks of alloantibody development [ adjusted relative risk ( RR ) 1Á34 , 95 % confidence interval ( 95 % CI ) 0Á97 - 1Á85 ] , especially when these infections were accompanied with long - standing fever ( RR 3Á06 , 95 % CI 1Á57 - 5Á