Rurality and pandemic influenza: geographic heterogeneity in the risks of infection and death in Kanagawa, Japan (1918-1919).

AIM To characterise the impact of rurality on the spread of pandemic influenza by exploring both the numbers of cases and deaths in Kanagawa Prefecture, Japan, from October 1918 to April 1919 inclusive. METHOD In addition to the numbers of influenza cases and deaths, population sizes were extracted from census data, permitting estimations of morbidity, mortality, and case fatality by 199 different regions (population 1.4 million). These outcomes were compared between four groups; cities (n=6), larger towns (38), smaller towns (101), and villages (54). RESULTS Whereas crude mortality in villages was lower than those of other population groups, the morbidity appeared to be the highest in villages, revealing significant difference compared to all cities and towns [risk ratio=0.601 (95% confidence interval: 0.600-0.602)]. Villages also yielded the lowest case fatality, the difference of which was statistically significant among four population groups (p=0.02). CONCLUSION Rurality did not show a predictive value of protection against pandemic influenza in Kanagawa. Lower morbidity in the towns and cities is likely explained by effective preventive measures in urban areas. High morbidity in rural areas highlights the potential importance of social distancing measures in order to minimise infections in the event of the next influenza pandemic.