Abstract
BackgroundThe sentinel surveillance system in Japan provides estimates of nationwide influenza incidence. Although prefectural influenza incidences can be estimated using data from the current surveillance system, such estimates may be imprecise.MethodsWe calculated the numbers of sentinel medical institutions (SMIs) needed in the surveillance system to estimate influenza incidences in prefectures, under the assumption that the standard error rates in 75% of influenza epidemic cases are less than 10%. Epidemic cases observed in 47 prefectures during the 2007/2008, 2008/2009, and 2009/2010 seasons, respectively, were used.ResultsThe present total number of SMIs was 6669. With respect to current standards, the increases required in prefectures ranged from 0 to 59, and the total increase required in the number of SMIs was 1668.ConclusionsWe used sentinel surveillance data for Japan to calculate the number of SMIs required to estimate influenza incidence in each prefecture.
Highlights
Many countries have created systems for sentinel surveillance of infectious diseases.[1,2,3,4,5] Such systems provide information that is essential for minimizing the burden and impact of an influenza outbreak, but incidence is not obtained directly using data from sentinels.[4,6] In Japan, sentinel surveillance of influenza is done as part of the National Epidemiological Surveillance of Infectious Diseases (NESID).[7]
Numbers of sentinel medical institutions (SMIs) and precision of prefectural influenza incidence estimates In 32 of the 47 prefectures, the standard number of SMIs in the prefecture was less than the number of SMIs needed for a critical proportion of 25% of epidemic cases, which means that the standard error rates for influenza incidence estimates in those prefectures would frequently (>75% of epidemic cases) exceed 10% and suggests that, under the current surveillance system, the precision of influenza incidence estimates would be insufficient in many prefectures
We calculated the numbers of SMIs needed for estimating prefectural influenza incidence under the assumption that the standard error rate of the incidence estimate in 75% of influenza epidemic cases was less than 10%
Summary
Many countries have created systems for sentinel surveillance of infectious diseases.[1,2,3,4,5] Such systems provide information that is essential for minimizing the burden and impact of an influenza outbreak, but incidence is not obtained directly using data from sentinels.[4,6] In Japan, sentinel surveillance of influenza is done as part of the National Epidemiological Surveillance of Infectious Diseases (NESID).[7]. Nationwide influenza incidence is estimated using data from SMIs.[10,11,12]. The sentinel surveillance system in Japan provides estimates of nationwide influenza incidence. Prefectural influenza incidences can be estimated using data from the current surveillance system, such estimates may be imprecise. Methods: We calculated the numbers of sentinel medical institutions (SMIs) needed in the surveillance system to estimate influenza incidences in prefectures, under the assumption that the standard error rates in 75% of influenza epidemic cases are less than 10%. With respect to current standards, the increases required in prefectures ranged from 0 to 59, and the total increase required in the number of SMIs was 1668. Conclusions: We used sentinel surveillance data for Japan to calculate the number of SMIs required to estimate influenza incidence in each prefecture
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