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Annual changes in the proportions of three classes based on antibody levels. (A) Patients aged ≥ 40 years, (B) patients aged < 40 years, (C) males, (D) females, (E) Human immunodeficiency virus (HIV)–infected patients, and (F) non-HIV-infected patients. Note: Antibody level class: low (100 titers), intermediate (200–800 titers), and high (1,600–12,800 titers).
