The Window Period:
A Gap in Existing Defenses Against
Transfusion-Transmitted Infections

Implementation of sensitive tests to detect pathogen-specific antibodies, antigens, and nucleic acids has greatly increased blood safety. However, the window period — the time between infection with a pathogen and the moment detection is possible by screening tests — continues to present a risk for disease transmission.

Test

Window Period is a Limitation of Current Screening.The window period is defined as the time between infection and detection. The length of the pathogen's window period depends on the pathogen's characteristics and the screening method used.
 
Blood collected from donors during the window period associated with HIV testing is thought to remain a source of HIV infection. Even when multiple tests are used for a single pathogen, infectious units may continue to enter the blood supply [43].
Estimated risk of collecting blood during the
infectious window period (US repeat donors, post NAT) [44]
Agent Window Period (days)* Risk (rate of infectious donations)
HBV
- no correction**
- corrected**		 59
59		 1:488,000
1:205,000
HCV
- Ab test only
- plus NAT		 70
70		 1:276,000
1:1,935,000
HIV
- Ab plus p24
- plus NAT		 16
11		 1:1,468,000
1:2,135,000
HTLV
- 1998-1999
- 2000-2001		 51
41		 1:514,000
1:2,993,000

* The window period quoted here may vary depending on the test employed.
** HBV correction compensates for the transient expression of HBsAg in acute infections.

Benefits of the INTERCEPT Blood System

Using a pathogen inactivation method such as the INTERCEPT Blood System can reduce or eliminate the risk from infectious window period donations. Although testing systems may ultimately narrow the window, they are unlikely to close it because they rely on testing only a portion of the transfused unit. The INTERCEPT Blood System is designed to inactivate the entire blood component unit, a fundamental advantage over testing systems.

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