Comparative study of preciseness in the regional variation of influenza in Japan among the National Official Sentinel Surveillance of Infectious Diseases and the National Database of Electronic Medical Claims.

In Japan, national official surveillance for influenza has been performed at about 5,000 sentinel hospitals/clinics by the National Official Sentinel Surveillance of Infectious Diseases (NOSSID). Meanwhile, all electronic medical claims nationwide in the National Database of Electronic Medical Claims (NDBEMC) were recently disclosed by the Ministry of Health, Labour and Welfare of Japan. We compared the regional variation of influenza incidence among prefectures between the NOSSID and NDBEMC. The data were extracted from NOSSID and the NDBEMC for the 2010/2011 through 2013/2014 seasons. We compared the data of both datasets season by season by using Spearman's rank correlation in each season. Spearman's rank correlation values for the four seasons were 0.7823, 0.3907, 0.4961 and 0.4543, and their p-values were less than 0.00005, 0.0066, 0.0004 and 0.0013, respectively. Statistically, regional variation of influenza incidence in NOSSID is not imprecise, but its correlation with the NDBEMC dataset is not so high. It is important to note this fact when interpreting regional variation in NOSSID.