Intradermal varicella skin test can assess varicella immunity

NEW YORK (Reuters Health) – An intradermal varicella skin test, using a diluted, inactivated solution of attenuated varicella vaccine, is a safe, sensitive, and specific method for assessment of immunity to varicella.

In a prospective, blinded study of 63 subjects, Dr. E. Somekh and colleagues from The Edith Wolfson Medical Center, Holon, Israel, examined the efficacy of this approach for predicting varicella susceptibility.

The researchers prepared the skin test solution with an inactivated OKA strain virus and diluted and stored the solution until it was injected intradermally into the patients. Prior to skin testing, they drew serum samples and used the indirect fluorescent antibody (IFA) method to analysis antibodies.

Forty-three subjects tested IFA antibody-positive, the authors report in the December issue of the Archives of Disease in Childhood. Of these, 41 reacted to the skin test. Of the 20 IFA-negative patients, one reacted to the skin test.

The investigators note that 16 patients had two serological tests performed 1 month apart. Of these, four tested negative with the skin test. "All four had negative serology on both samples," they add.

One month after the skin test, 6 of the 12 patients who were IFA-positive showed at least a fourfold rise in the antibody titre. "The specificity and sensitivity of the skin test compared to the IFA assay were both 95%, and the positive and negative predictive values were 97% and 90%, respectively," Dr. Somekh and colleagues report.

"We believe that if these results are reproduced in larger studies, this test may prove to be an accessible clinical tool when facing a varicella dilemma." The test may be particularly useful for pregnant and immunocompromised patients, they add.

Arch Dis Child 2001;85:484-486.

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