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1.  Estimation of Influenza Incidence by Age in the 2011/12 Seasons in Japan using SASSy 
So far, it is difficult to show the incidence rate of influenza in the official sentinel surveillance in Japan. Hence we construct the system which record infectious diseases at schools, kindergartens, and nursery schools, and then can show the accurate incidence rate of influenza in children by age/grade.
So as to develop more effective countermeasures against influenza, timely and precise information about influenza activity at schools, kindergartens, and nursery schools may be helpful. At the Infectious Diseases Surveillance Center of the National Institute of Infectious Diseases, a School Absenteeism Surveillance System (SASSy) has been in operation since 2009. SASSy monitors the activity of varicella, mumps, mycoplasma pneumonia, pharyngoconjunctival fever, hand-foot-mouth disease, influenza, and many other infectious diseases in schools. In 2010, SASSy was extended to the Nursery School Absenteeism Surveillance System (NSASSy). These systems record the number of absentees due to infectious diseases in each class of all grades of schools every day. As a powerful countermeasure to the pandemic flu of 2009, SASSy was activated in 9 prefectures, in which included more than 6000 schools, and it is gradually being adopted in other prefectures. As of February 2012, 18 prefectures and 4 big cities, which together comprised 15,700 schools (about 35% of all schools in Japan), utilized SASSy. NSASSy is used in more than 4100 nursery schools, which is about 18% of all nursery schools in Japan. Some studies of similar systems were performed in the UK (1), Hong Kong (2), and the USA (3,4), examined surveillance systems for monitoring infectious disease incidence, but the systems to construct in those studies do not operate nationwide like SASSy or NSASSy, and they cannot provide influenza incidence rates in children.
All schools, kindergartens, and nursery schools in the community, enter data of the absentees due to infectious diseases into the system every day, thereby providing real-time data regarding infectious diseases prevalent in schools, to the schools around, school boards, public health centers, local governments, and medical professionals. It analyzed data for the 2011/2012 season (from September 1, 2011 to March 31, 2012) mainly, but also two seasons (2010/2011 and 2011/2012) were compared in some prefectures. In total, 12 prefectures, which comprised 2,352,839 children, were participated in 2011/2012 season. In the 2010/2011 season, 1,795,766 children of 9 prefectures were analyzed.
The incidence rate in the first grade of elementary schools is the highest both in the two seasons. The highest incidence rate in this grade distributes from 17.8% to 40.3% in 2011/2012 season, and from 11.0% to 30.7% in 2010/2011 season.
This study proved SASSy and NSASSy are quite useful for monitoring of influenza outbreak in schools and it will be gold standard of surveillance for school children in Japan. The present study also showed incidence rate of influenza in children at schools, kindergartens, and nursery schools, and proved the highest incidence was in the first grade of the elementary school. This is the first finding using such the huge number of subjects, which is more than 2 million. The intervention targeting to the weak age/grade is necessary for effective countermeasure and control of influenza and other infectious diseases.
PMCID: PMC3692790
Surveillance; Influenza; School Absenteeism
2.  Transmission of Bordetella holmesii during Pertussis Outbreak, Japan 
Emerging Infectious Diseases  2012;18(7):1166-1169.
We describe the epidemiology of a pertussis outbreak in Japan in 2010–2011 and Bordetella holmesii transmission. Six patients were infected; 4 patients were students and a teacher at the same junior high school. Epidemiologic links were found between 5 patients. B. holmesii may have been transmitted from person to person.
PMCID: PMC3376812  PMID: 22709586
Bordetella infections; pathogen transmission; outbreak; Bordetella holmesii; Bordetella pertussis; pertussis; bacteria; Japan
3.  Novel measurement of spreading pattern of influenza epidemic by using weighted standard distance method: retrospective spatial statistical study of influenza, Japan, 1999–2009 
Annual influenza epidemics occur worldwide resulting in considerable morbidity and mortality. Spreading pattern of influenza is not well understood because it is often hampered by the quality of surveillance data that limits the reliability of analysis. In Japan, influenza is reported on a weekly basis from 5,000 hospitals and clinics nationwide under the scheme of the National Infectious Disease Surveillance. The collected data are available to the public as weekly reports which were summarized into number of patient visits per hospital or clinic in each of the 47 prefectures. From this surveillance data, we analyzed the spatial spreading patterns of influenza epidemics using weekly weighted standard distance (WSD) from the 1999/2000 through 2008/2009 influenza seasons in Japan. WSD is a single numerical value representing the spatial compactness of influenza outbreak, which is small in case of clustered distribution and large in case of dispersed distribution.
We demonstrated that the weekly WSD value or the measure of spatial compactness of the distribution of reported influenza cases, decreased to its lowest value before each epidemic peak in nine out of ten seasons analyzed. The duration between the lowest WSD week and the peak week of influenza cases ranged from minus one week to twenty weeks. The duration showed significant negative association with the proportion of influenza A/H3N2 cases in early phase of each outbreak (correlation coefficient was −0.75, P = 0.012) and significant positive association with the proportion of influenza B cases in the early phase (correlation coefficient was 0.64, P = 0.045), but positively correlated with the proportion of influenza A/H1N1 strain cases (statistically not significant). It is assumed that the lowest WSD values just before influenza peaks are due to local outbreak which results in small standard distance values. As influenza cases disperse nationwide and an epidemic reaches its peak, WSD value changed to be a progressively increasing.
The spatial distribution of nationwide influenza outbreak was measured by using a novel WSD method. We showed that spreading rate varied by type and subtypes of influenza virus using WSD as a spatial indicator. This study is the first to show a relationship between influenza epidemic trend by type/subtype and spatial distribution of influenza nationwide in Japan.
PMCID: PMC3495731  PMID: 22713508
Weighted standard distance; Influenza; Spatial compactness
4.  Real-time Prescription Surveillance and its Application to Monitoring Seasonal Influenza Activity in Japan 
Real-time surveillance is fundamental for effective control of disease outbreaks, but the official sentinel surveillance in Japan collects information related to disease activity only weekly and updates it with a 1-week time lag.
To report on a prescription surveillance system using electronic records related to prescription drugs that was started in 2008 in Japan, and to evaluate the surveillance system for monitoring influenza activity during the 2009–2010 and 2010–2011 influenza seasons.
We developed an automatic surveillance system using electronic records of prescription drug purchases collected from 5275 pharmacies through the application service provider’s medical claims service. We then applied the system to monitoring influenza activity during the 2009–2010 and 2010–2011 influenza seasons. The surveillance system collected information related to drugs and patients directly and automatically from the electronic prescription record system, and estimated the number of influenza cases based on the number of prescriptions of anti-influenza virus medication. Then it shared the information related to influenza activity through the Internet with the public on a daily basis.
During the 2009–2010 influenza season, the number of influenza patients estimated by the prescription surveillance system between the 28th week of 2009 and the 12th week of 2010 was 9,234,289. In the 2010–2011 influenza season, the number of influenza patients between the 36th week of 2010 and the 12th week of 2011 was 7,153,437. The estimated number of influenza cases was highly correlated with that predicted by the official sentinel surveillance (r = .992, P < .001 for 2009–2010; r = .972, P < .001 for 2010–2011), indicating that the prescription surveillance system produced a good approximation of activity patterns.
Our prescription surveillance system presents great potential for monitoring influenza activity and for providing early detection of infectious disease outbreaks.
PMCID: PMC3846340  PMID: 22249906
Surveillance; influenza; real-time surveillance; prescriptions; pharmacy; anti-influenza virus; automatic surveillance; early response
5.  Pandemic (H1N1) 2009 Transmission during Presymptomatic Phase, Japan 
Emerging Infectious Diseases  2011;17(9):1737-1739.
During an epidemiologic investigation of pandemic influenza (H1N1) 2009 virus infection in May 2009 in Osaka, Japan, we found 3 clusters in which virus transmission occurred during the presymptomatic phase. This finding has public health implications because it indicates that viral transmission in communities cannot be prevented solely by isolating symptomatic case-patients.
PMCID: PMC3322057  PMID: 21888808
Influenza; human; influenza A virus; viruses; H1N1 subtype; pandemic (H1N1) 2009; disease outbreaks; infectious disease transmission; infectious disease incubation period; contact tracing; dispatch
6.  BioCaster: detecting public health rumors with a Web-based text mining system 
Bioinformatics  2008;24(24):2940-2941.
Summary: BioCaster is an ontology-based text mining system for detecting and tracking the distribution of infectious disease outbreaks from linguistic signals on the Web. The system continuously analyzes documents reported from over 1700 RSS feeds, classifies them for topical relevance and plots them onto a Google map using geocoded information. The background knowledge for bridging the gap between Layman's terms and formal-coding systems is contained in the freely available BioCaster ontology which includes information in eight languages focused on the epidemiological role of pathogens as well as geographical locations with their latitudes/longitudes. The system consists of four main stages: topic classification, named entity recognition (NER), disease/location detection and event recognition. Higher order event analysis is used to detect more precisely specified warning signals that can then be notified to registered users via email alerts. Evaluation of the system for topic recognition and entity identification is conducted on a gold standard corpus of annotated news articles.
Availability: The BioCaster map and ontology are freely available via a web portal at
PMCID: PMC2639299  PMID: 18922806
7.  Geographic and Temporal Trends in Influenzalike Illness, Japan, 1992–1999 
Emerging Infectious Diseases  2004;10(10):1822-1826.
Kriging analysis improved visualization and understanding of trends in seasonal ILI activity in Japan.
From 1992 to 1999, we analyzed >2.5 million cases of influenzalike illness (ILI). Nationwide influenza epidemics generally lasted 3–4 months in winter. Kriging analysis, which illustrates geographic movement, showed that the starting areas of peak ILI activity were mostly found in western Japan. Two spreading patterns, monotonous and multitonous, were observed. Monotonous patterns in two seasons featured peak ILI activity that covered all of Japan within 3 to 5 weeks in larger epidemics with new antigenic variants of A/H3N2. Multitonous patterns, observed in the other five seasons, featured peak ILI activity within 12 to 15 weeks in small epidemics without new variants. Applying the kriging method allowed better visualization and understanding of spatiotemporal trends in seasonal ILI activity. This method will likely be an important tool for future influenza surveillance in Japan.
PMCID: PMC3323282  PMID: 15504270
Influenza; surveillance system; GIS; kriging; pandemic; research
8.  Bacillus anthracis Bioterrorism Incident, Kameido, Tokyo, 1993 
Emerging Infectious Diseases  2004;10(1):117-120.
In July 1993, a liquid suspension of Bacillus anthracis was aerosolized from the roof of an eight-story building in Kameido, Tokyo, Japan, by the religious group Aum Shinrikyo. During 1999 to 2001, microbiologic tests were conducted on a liquid environmental sample originally collected during the 1993 incident. Nonencapsulated isolates of B. anthracis were cultured from the liquid. Multiple-locus, variable-number tandem repeat analysis found all isolates to be identical to a strain used in Japan to vaccinate animals against anthrax, which was consistent with the Aum Shinrikyo members’ testimony about the strain source. In 1999, a retrospective case-detection survey was conducted to identify potential human anthrax cases associated with the incident, but none were found. The use of an attenuated B. anthracis strain, low spore concentrations, ineffective dispersal, a clogged spray device, and inactivation of the spores by sunlight are all likely contributing factors to the lack of human cases.
PMCID: PMC3322761  PMID: 15112666
Bacillus anthracis; bioterrorism; anthrax; epidemiology; Aum Shinrikyo; Japan

Results 1-8 (8)