The incidence and consequences of cytomegalovirus transmission via blood transfusion to low birth weight premature infants in Aberdeen
The acquisition of cytomegalovirus (CMV) infection following blood transfusion has been recognised for over 20 years. Prospective studies in the late 1960's and early 70's demonstrated that this infection was relatively frequent, particularly when patients were multitransfused. In assessing the clinical importance of CMV infection, critical distinctions must be made between infection and significant disease. This is primarily dependent on the immunocompetence of the invaded host. In the child or adult with a normal immune function, CMV infection usually results in asymptomatic seroconversion or is manifested as a mild heterophile-negative mononucleosis syndrome. There is minimal morbidity associated with these infections. Among healthy people the prevalence of CMV acquisition depends on age, socioeconomic conditions and the particular place where the investigations are carried out. In contrast, CMV may be associated with significant morbidity and mortality in immunocompromised patients eg, premature infants, children with immunodeficiency syndromes, patients on chemotherapy and transplant recipients. CMV infections in such patients may be either the result of reactivation of latent virus, since CMV frequently persists in the host after a primary infection or a de novo primary infection. In newborn infants, the role of blood transfusion in causing CMV infection is easier to ascertain, because reactivation of latent CMV is not a complicating factor. Premature infants, receiving blood transfusions (a very common practice) represent a special subpopulation in immunocompromised recipients. Numerous studies have identified 3 particularly high risk groups in this neonatal context: 1. maternal and neonatal seronegativity 2. transfusion of more than 50 mls of blood in toto per infant, particularly when the number of donors is high (&62 4) 3. very low birth weight; usually less than 1500 gms. Moreover these studies have convincingly shown that CMV infection can be significantly reduced by choosing seronegative blood for seronegative infants. However the provision of such blood would pose problems involving significant expense. Seronegative donors would have to be found from the routine donor panels and they would have to be tested prior to every blood donation, because of the possiblity of silent seroconversion. This involves the use of expensive reagents and requires organisational expertise regarding the appropriate timing of tests, keeping adequate stocks of such bloods, etc. Therefore before specific recommendations can be formulated with regard to the use of CMV seronegative blood for controlling CMV infections, it is necessary to study the local circumstances because the prevalence of CMV seronegativity varies in different populations. Moreover, recent studies have shown that the clinical consequences of CMV infection following blood transfusions seems to be diminishing. The reasons for this are not readily identifiable, but may be related to a number of factors, including the volume of blood transfused, the number of donor exposures and importantly a significant change in the make up of the blood donor population. Whatever the reason some centres have concluded, after local studies not to provide CMV screened blood for their sick nursery babies, even for the ones who are at highest risk of CMV infection. In fact a recent nationwide survey run by the American Association of Blood Banks and the College of American Pathologists in 1987 show that as many as 40% of community hospitals and 20% of children's hospitals do not provide blood or blood components with a reduced risk of CMV transmission for their neonates. With such conflicting policies on CMV screening it is therefore all the more important to evaluate the local clinical morbidity and/or mortality in at risk infants, induced by CMV infection via random (CMV unscreened) blood transfusions, which is current practice in our centre. Secondary to the main aims of this work, it was also possible to study: (a) the prevalence of CMV seropositivity amongst the blood donor population in the North East of Scotland and to study in some detail recent CMV infections both serologically and virologically in such donors. (b) the incidence of congenital CMV infection and CMV infection acquired during pregnancy in a select subpopulation of mothers. Since the data on CMV seroprevalence throughout different parts of the UK are scanty, the opportunity was taken to obtain some data on the subject. Although the information is of limited comparable value, the aim was to provide data both on the overall CMV donor carrier rate in different parts of the UK and also on the methodology used to detect it.