No 18 - 2012

Blood donor screening 2010 and 2011

In 2010 and 2011, respectively, 337,278 and 319,094 portions of blood were screened and a total of 33,359 and 19,585 candidate donors were tested. Candidate donors are first-time donors, i.e. donors who have not previously donated blood and donors returning to donate blood after more than five years of absence. Candidate donors did not donate blood, but simply provided a blood sample. The number of positive donors is presented in Table 1. 

NAT screening (nucleic acid amplification technique) of donor blood for HIV, hepatitis B and C virus (HBV and HCV) was introduced by law on 1 January 2009, EPI-NEWS 2/10.

HIV

Two donors were tested positive for HIV in 2010. One was a male who had donated blood more than five years back. Through look-back it was established that the blood had not been used for donation. The other was an active male donor who had probably been infected by a female sex worker. Look-back identified no infected recipients.

In 2011, one multiple donor tested positive for HIV; the donor had probably been infected by a sex worker in Thailand. No infected recipients were found.

HBV

In 2010 and 2011, respectively, 13 and seven blood donors tested positive for HBV: four females and 16 males. The median age was 46 years (range 19-65 years).
A total of 12 persons were candidate donors, among whom ten were born in countries where hepatitis B occurs endemically. For one person, the mode of infection was unknown, and the mother of another had been infected by HBV.

A total of eight multiple donors tested positive, six of whom only by NAT screening. Presumably, these six donors had a chronic hepatitis B infection in which HBsAg (hepatitis B surface antigen) is undetectable or only periodically detectable in the blood due to low virulence. At look-back, three recipients showed signs of HBV infection: One recipient had had an acute infection with detectable HBV DNA and subsequent sero-conversion to anti-HBs. This recipient had probably been infected by a NAT-screened donation which had tested negative. Consequently, the donor in question was hepatitis B core antibody-positive and intermittently NAT screening-positive.

Two recipients had antibodies (one had anti-HBc and one had anti-HBc and anti-HBe) due to previous hepatitis B infection.
In these two recipients, the possibility that a blood transfusion had caused the infection could not be investigated further as the recipients did not test positive to the virus, but only to antibodies. None of the recipients had experienced any clinical signs of hepatitis.

HCV

In 2010 and 2011, respectively, three and four donors were tested positive for HCV: three females and four males. Their median age was 42 years (range 24-65 years).

Five of these were candidate donors: one was born in an endemic area, one had probably been infected via a blood transfusion in the 1970s, one probably via a piercing or tattoo, and the mode of infection was unknown in two persons.
Among multiple donors, one had donated blood prior to the introduction of hepatitis C blood screening. This person had subsequently been pierced. The mode of infection for the other multiple donor was unknown.

HTLV I/II

All candidate donors were also screened for HTLV I/II (Human T-lymphotropic virus). One donor tested positive for HTLV I in 2010. The mode of infection was unknown.

Commentary

In 2010 as well as in 2011, a total of four persons only tested positive to HBV by NAT.

Before NAT screening was introduced, multiple donors who tested positive to HIV, HBV or HCV had been exposed to a known infection risk. However, NAT screening reveals HBV infections even in cases with very low virus replication. Donors with low-virulent HBV infections were not diagnosed using the antigen tests which previously comprised the screening of donor blood. Consequently, recipients have been found who may have been infected by donors in Denmark and who were not previously considered capable of transferring HBV infection.

This raises the question of whether and to which extent look-back should be performed for recipients who have received blood from multiple donors who were tested HBV NAT-positive at future donations. Furthermore, the introduction of mandatory screening for hepatitis B core antibodies of all candidate donors should be considered along with the exclusion of all donors who carry markers of a precious HBV infection.

Changes in blood donor screening

The statutory screening requirement of candidate donors for HTLV I/II was repealed on 1 January 2012 in response to a very low occurrence among donors and the fact that all Danish donor blood is leucocyte-filtered, a process which removes any leukocytes capable of transferring HTLV I/II infection. In contrast hereto, the HBV screening has been intensified as several Danish blood banks have initiated screening of candidate donors for antibodies against hepatitis B core antigen. As described elsewhere in the present issue of EPI-NEWS, HBV screening was intensified because even NAT screening may leave very low virus levels undetected in donors with so-called occult hepatitis B infection and these cases may be infectious. As from January 2012, collection of blood from candidate donors has been permitted.

(A.H. Christiansen, S. Cowan, Dept. of Infectious Disease Epidemiology, L. Harritshøj, H. Ullum, Dept. of Clin. Immunology, Copenhagen University Hospital, C. Erikstrup, Dept. of Clin. Immunology, Aarhus University Hospital)

2 May 2012