The risk of infection with bloodborne viruses following transfusion of screened blood is very small, with the greatest threat to patients the donation of blood by seronegative donors during the window period prior to seroconversion, the authors report.
They estimated the risk of transmitting the HIV, hepatitis C virus, and the hepatitis B virus from screened blood units donated during the window period following a recent, undetected infection. Using data on 586,507 persons who each donated blood more than once between 1991 and 1993 at five blood centers, they calculated the incidence rates of seroconversion among those whose donations passed all the screening tests used. Rates were adjusted these rates for the estimated duration of the infectious window period for each virus.
Among donors whose units passed all screening tests, the risks of giving blood during an infectious window period were estimated as follows: for HIV, one in 493,000; for HCV, one in 103,000; and for HBV, one in 63,000.
HBV and HCV accounted for 88% of the aggregate risk of one in 34,000. However, new screening tests that shorten the window periods for the viruses should reduce the risks by 27% to 72%.
Although new techniques of testing will move closer to the goal of zero risk, it is unlikely that any test or combination of tests will be 100% effective in detecting window-period infections.
"Therefore, the yield and cost effectiveness of new, direct assays for virus will be low, and decisions about their implementation will be difficult, given the many demands on health care resources," they conclude. *
Cobben NAM, Drent M, Jonkers M, et al. Outbreak of severe Pseudomonas aeruginosa respiratory infections due to contaminated nebulizers. Jrl Hosp Infect 1996; 33:63-70.
Investigators traced 21 cases of pulmonary infection caused by Pseudomonas aeruginosa to nebulizers that were improperly stored after washing.
P. Aeruginosa was isolated from four of 22 nebulizers tested and linked to patients via molecular epidemiology. The data provided evidence for the relation between P. Aeruginosa as a cause of infection and the contamination of the nebulizers. When nebulizer mouthpieces were changed every 24 hours and sterilized between patients, no more contamination occurred, and the outbreak ceased.
Although it was thought adequate, disinfection methods were used for the nebulizers. They were stored in a damp condition, the authors noted, concluding that a disinfection protocol must include instructions for storage and be monitored regularly.
They cited the following protocol for use of a nebulizer: wash hands, refill before use from sterile container or single-use vial. After use (or at least daily) wash in hot water, dry with a paper towel, immerse in glutaraldehyde for 30 minutes, and never use tap water.
Before the outbreak they also used glutaraldehyde and stored the nebulizers mounted ready for use. Following the problem, they began changing the mouthpieces daily and sterilizing the other components with ethylene oxide in between patients.
"This proved highly effective in prevention of cross infection despite admission of further cases of severe respiratory infections with P aeruginosa," they concluded. *
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