The proportions of the anti-PT IgG titers ≥ 62.5 IU/mL were 11.4%, 12.2%, 9.1%, 5.8%, and 6.2% in 3–5, 6–15, 16–25, 26–35, and 36–57 years old, respectively, in Nha Trang, 2019 (age in 2019); however, we did not regard them as the estimated prevalence of recent infection in 2019 because the subjects were part of the 2017 participants and were not sampled from the population appropriately. Here, F2 is linked to infection.