The prevalence of H. pylori and severity of atrophy were examined in 1381 patients including 289 patients examined in the 1970s (158 men; mean age, 44.9 years),
787 in the 1990s (430 men; 44.2 years), and 305 in the 2010s (163 men; 53.2 years).
Overall, the prevalence of H. pylori infection decreased significantly from 74.7% (1970s) to 53% (1990s) and 35.1% (2010s) (p < .01).

ピロリ感染率のサンプルサイズが305で35.1%が陽性ということだから107/305だろね。

> binom::binom.exact(107,351,conf.level = 0.99)
method x n mean lower upper
1 exact 107 351 0.3048433 0.2431662 0.3719357

99%信頼区間が 24　〜　37% ではあるけど。