Characteristics of non-hemophiliac patients aged 15 years or greater who had baseline and follow-up indirect hemagglutination (IHA) assays.

Abbreviations: 95% CI, 95% confidence interval; 100 PY, 100 persons-years of observation; IDU: intravenous drug user; IQR, interquartile range; MSM, men who have sex with men. Note: *Seroconversion from 0 at baseline to ≧128 at second tests. Rate ratio (MSM vs. patients of other risk groups): 13.87 (95% CI, 1.866, 103.1). ** Seroconversion from 0 at baseline to ≧128 at second tests; or from any titer at baseline to 4-fold rise or greater than baseline values. Rate ratio: 19.15 (95% CI, 2.61, 140.6).