Factors influencing the decision to test young infants for herpes simplex virus infection.

In a nested case-control study of 478 infants < or =90 days of age, one-third of infants undergoing cerebrospinal fluid herpes simplex virus (HSV) testing by polymerase chain reaction were >28 days of age. Recognized factors, such as mode of delivery, were not associated with HSV testing. The factors currently used by physicians in the decision to order this test do not best reflect the likelihood of HSV infection.