Akira Endo1, Hiroshi Nishiura2. 1. Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. 2. Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan; CREST, Japan Science and Technology Agency, Saitama, Japan. Electronic address: nishiurah@m.u-tokyo.ac.jp.
Abstract
BACKGROUND: Vivax malaria with two distinct (short- and long-term) incubation periods has been prevalent in the Republic of Korea since its re-emergence in 1993. As part of countermeasures, mass chemoprophylaxis has been conducted since 1997 among military personnel, a high risk group. To assess the population effectiveness of chemoprophylaxis, the time-dependent reproduction number was estimated in the present study. METHODS: A renewal process has been employed, estimating the yearly effective reproduction number (Ry) from 1993 to 2012 using a maximum likelihood estimation method. Akaike Information Criterion (AIC) was computed to identify the best-fit model with a time-dependent trend that coincides with the timing of mass chemoprophylaxis. RESULTS: The estimates of Ry revealed an overall declining trend from 1997 to 2012. Despite small fluctuations in 2005 and 2009, Ry was brought to be close to unity since 2000. An extrapolated model of the time-dependent reproduction number with the smallest AIC indicated that there was an abrupt decline in secondary transmission from 1997 to 1998. CONCLUSION: The epidemic of vivax malaria in the Republic of Korea has been on the whole brought under control in the last decades. Mass chemoprophylaxis assisted the decline in secondary transmissions from its second year, which presumed to have reflected the effect of long incubation period and expansion of the coverage.
BACKGROUND: Vivax malaria with two distinct (short- and long-term) incubation periods has been prevalent in the Republic of Korea since its re-emergence in 1993. As part of countermeasures, mass chemoprophylaxis has been conducted since 1997 among military personnel, a high risk group. To assess the population effectiveness of chemoprophylaxis, the time-dependent reproduction number was estimated in the present study. METHODS: A renewal process has been employed, estimating the yearly effective reproduction number (Ry) from 1993 to 2012 using a maximum likelihood estimation method. Akaike Information Criterion (AIC) was computed to identify the best-fit model with a time-dependent trend that coincides with the timing of mass chemoprophylaxis. RESULTS: The estimates of Ry revealed an overall declining trend from 1997 to 2012. Despite small fluctuations in 2005 and 2009, Ry was brought to be close to unity since 2000. An extrapolated model of the time-dependent reproduction number with the smallest AIC indicated that there was an abrupt decline in secondary transmission from 1997 to 1998. CONCLUSION: The epidemic of vivax malaria in the Republic of Korea has been on the whole brought under control in the last decades. Mass chemoprophylaxis assisted the decline in secondary transmissions from its second year, which presumed to have reflected the effect of long incubation period and expansion of the coverage.