Varicella arthritis diagnosed by polymerase chain reaction.

We report a 2-year-old girl who developed acute arthritis of the left knee 4 days after the onset of a typical varicella infection. She was first thought to have pyogenic arthritis caused by Staphylococcus aureus. Accordingly, oxacillin was administered upon hospitalization. On the third day after hospitalization, bacterial cultures of the synovial fluid and blood showed no growth and oxacillin was discontinued. Although a viral culture of the synovial fluid for varicella-zoster virus (VZV) was negative, varicella DNA was identified by means of polymerase chain reaction (PCR) with VZV-specific primers. The patient recovered spontaneously. To differentiate this condition from septic arthritis is important. PCR is a sensitive technique that can demonstrate the presence of VZV DNA in synovial fluid, even if viral cultures are negative.