Change in use of asthma as a diagnostic label for wheezing illness in schoolchildren.

antibody but positive by the polymerase chain reaction confirmed the reproducibility of this technique. Susceptible patients must be at some risk of infection when given transfusions of blood from subjects such as these who carry the virus. Thus the polymerase chain reaction clearly has an important role in screening blood products as well as being a powerful test in diagnostic virology. I W'ilhelm JA, 1\atter L, Schopfer K. The risk of transmitting cvtomegalov irus to patients receiving blood transfusions.]' InJect IDis 1986;154:169-71. 2 Saiki RK, (,elfond D)H, Stoffel S, et al. Primer-directed enzymatic amplification of DNA with a thermostable DNA polymerase. Science 1988;239:487-94. 3 Stcrnberg RM, IThomsen DR, Stinsky ME. Structural analysis of the major immediate earIy gene region of human cytormegalovirus. IJ irol 1984;49: 190-9. 4 Kwok S, Higuchi R. Avoiding false positives with P'CR. Naturc 1989;339:237-8. 5 Yeager AS, Grumet FC, Hafleigh EB, Arvin AM, Bradley JS, Prober CG. Prevention of transfusion-acquired cytomcgalovirus infections in newborn infants.] Pediatr 1981;98:281-7.