Monitoring viral incidence rates: tools for the implementation of European Union regulations

European legislation requires manufacturers of plasma products to report epidemiological data on human immunodeficiency virus, hepatitis B virus and hepatitis C virus in donor populations. The incidence rates of such infections are directly related to the risk of infection transmission. We propose two statistical tests to evaluate these incidence rates.

Infection data of the four Dutch blood collection centres from 2003 through 2006 were analysed. For transversal comparison of centres and detection of increased incidence rates, a new statistical test was developed (outlier test). For longitudinal detection of trends in incidence rates, a generic test for trend is proposed. The power and risk of non-detection are evaluated for both tests.

Application of the outlier test did not reveal any significantly increased incidence rates among centres in The Netherlands. The test for trend showed no significant increase in incidence rates in individual centres, but on national level a statistically significant increase in hepatitis C virus incidence was observed (P-value of 0.01).

The proposed tests allow signalling of outlier centres and trends in incidence rates both at individual centre and at national levels. Graphical support and the use of as much relevant historical data as possible is recommended. The statistical tests described are generic and can be applied by any blood establishment and plasma fractionation institute.