[A study on the HA amount of HA influenza vaccination on efficacy and safety in infants]

[An Epidemiological Study on an Influenza Outbreak at Day Nurseries and Nursing Institutions in Gunma]

OBJECTIVE

The features of influenza outbreaks (IOs) at day nurseries (DN), facilities for the handicapped (FH), and care homes for the elderly (CHE) are unclear. The aim of this study was to clarify these features at each institution.

MATERIALS AND METHODS

The authors examined IOs (n = 258) that occurred at DN, FH, or CHE in Gunma Prefecture between 2012 and 2014, and the characteristics of such IOs were investigated epidemiologically. Results : (1) DN had a higher number of users, a higher user-to-staff member ratio, and a lower number of staff members compared to those at FH. and CHE. (2) The rate of IOs was highest at DN. (3) At DN and CHE, the occurrence of IOs during the early period of the influenza season in the community was higher than that during the late period of the influenza season in the community. (4) IOs persisted for longer at DN. (5) The IOs attack rates were highest at FH during the early, late, and total periods, although those at FH and CHE decreased slightly during the late period. (6) The attack rates of staff members at CHE during the early period and at FH during the late period were high. The attack rate of staff members at CHE significantly decreased during the late period.

CONCLUSIONS

The occurrence of IOs at DN and CHE will be influenced by influenza epidemicity seen outside of the institutions. IOs often occurred and were prolonged at DN, which can be explained by the high rate and frequency of secondary infection resulting from the very close contact among users. At CHE, the attack rate increased due to the very close contact between users and staff members, especially during the early period; however, the attack rate at CHE during the late period decreased due to the prevention of secondary infection. At FH, the attack rates were higher compared to those at DN and FH, which was influenced by the high degree of contact among users and between users and staff members. The spread and prolongation of IOs will be influenced by the users',high degree of behavior, the high degree of contact between users, and the high degree of contact among users and between users and staff members. Prevention of IOs and their prolongation and spread should be conducted according to factors that affect the duration and spread of IOs, as described above.