Trends and variations in infant mortality among 47 prefectures in Japan.

Objectives: To determine IMR trends and regional variations among 47 prefectures in Japan and to identify associated population-based factors.

Methods: We conducted an ecological study of infant mortality rate (IMR) by analyzing publicly available data from the Ministry of Health, Labour and Welfare of Japan. Outcome measure for trend is the IMR for each of 47 prefectures from 1999 to 2007; for variation, IMRs for 2006 and 2007 in each prefecture were averaged. We considered as covariates prefecture-level variables related to public health, socio-economic status, clinical services and health care facilities. We conducted multivariate statistical analyses to determine covariates most strongly associated with both 1999-2007 IMR trends and 2006-2007 IMR.

Results: The mean IMR decreased from 3.42 deaths per 1000 live births (range 2.1 to 5.1) in 1999 to 2.54 (range 1.5 to 4.4) in 2007; reductions were greater in prefectures with higher concentrations of public health nurses (PHNs) and nurses. In 2006-2007, nine prefectures had IMRs ≤ 2.25; eight had IMRs ≥ 3.0. When low-, moderate- and high-IMR prefectures were compared, per capita PHNs, maternal education, centralized water supply and household income were identified as significant covariates.

Conclusions: Both national and prefecture-level IMR in Japan decreased from 1999 to 2007; however, the degree of reduction varied by prefecture. Given that more nurses and PHNs per capita were associated with greater IMR reductions from 1999 to 2007 and more PHNs with lower 2006-2007 IMRs, distribution of preventive health services may play a major role in reducing regional disparities in IMR.