Background The Great East Japan Earthquake and subsequent tsunami and nuclear disaster on 11 March 2011 had a short-term influence on the increase in emergency department visits and hospital admissions due to various diseases. However, it remains unclear whether the earthquake and tsunami disaster affected the long-term health conditions of people in the affected areas.

Methods Using a national inpatient database in Japan, we investigated people's ambulatory care sensitive conditions (ACSCs), which are defined as conditions for which effective management and treatment should prevent admission to a hospital. We compared the number of admissions for ACSCs before-quake (July 2010 to February 2011) with after-quake (July 2012 to February 2013) periods in the disaster area compared with other areas using a difference-in-differences design. Linear regression models with the interaction between periods and areas were used to estimate the impact of the earthquake on admissions for ACSCs.

Results No significant difference in difference was seen in preventable ACSCs (where immunisation and other interventions can prevent illness) or chronic ACSCs (where effective care can prevent flare-ups), while acute ACSCs (where early intervention can prevent more serious progression) increased significantly (3.3 admissions per 100 000 population; 95% CI 0.4 to 6.3; p=0.028).

Conclusions Preventable and chronic ACSCs may have increased just after the earthquake and then immediately decreased. However, avoidable admissions due to acute ACSCs remained high in the long term after the earthquake and tsunami disaster.