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Flowchart for the studies. Inclusion criteria for case patients and controls were age ≥40 years; no previous Read Code or International Classification of Diseases, 10th revision, code for postherpetic neuralgia; no previous prescription for systemic acyclovir, valacyclovir, or famciclovir (Denmark only); and registration with current general practice for ≥12 months before the index date (United Kingdom only).
