the hospitalization period in acute care hospitals in japan is regulated by several factors including disease severity , general condition of patients , and therapeutic intervention of surgery and/or other intensive cares . these factors suggest that the hospitalization period is one index for evaluating quality of medical care . namely , reducing hospitalization days is a reliable index for improving patient prognosis and quality of medical care in japan . the diagnosis procedure combination ( dpc ) system was introduced in 2003 in japanese medical hospitals authorized to treat patients with health insurance . the dpc system was practiced in 55% of all general sickbeds in 1,585 hospitals with a total of 492,256 sickbeds . the main purpose of introducing the dpc system into intensive care hospitals in japan is to maintain a supply of above average medical care . the dpc system regulates diagnostic and therapeutic approaches in each dpc code for standardization of medical care , and regulates the hospitalization period in each dpc code . in the dpc , hospital days are set for every identical diagnostic classification ( dpc code ) as follows : period 1 : < 25 percentile of hospital days ; period 2 : < 50 percentile of hospital days ; and period 3 : within mean    2sd . the aim of the present study was to evaluate causative ( risk ) factors for prolongation of hospitalization days in excess of period 3 according to the dpc system in 20,869 patients in saga university hospital . the evaluated factors for prolongation of hospitalization period in the present study were hospitalization status with emergency or scheduled admission , selected ward of emergency care unit ( ecu ) , intensive care unit ( icu ) , beds for general patients , and comorbidities regarding diabetes mellitus and infectious diseases . in the dpc system , hospital days are set for every identical diagnostic classification ( dpc code ) as follows : period 1 : < 25 percentile of hospital days ; period 2 : < 50 percentile of hospital days ; and period 3 : within mean  +  2sd . a patient whose hospitalization period exceeds period 3 is recognized as a significantly prolonged case compared with the national case in each identical diagnostic classification ( dpc code ) . according to the dpc definition , 20,876 patients hospitalized in saga university hospital from april 1 , 2012 , to february 28 , 2015 , were classified into two groups : group i , with hospitalization days within period 3 , and group ii , with hospitalization days exceeding period 3 . in groups i and ii , the present study evaluated age , gender , hospitalization days , mortality rate during hospitalization , number of days in period 3 in each dpc code , emergency or planned hospitalization , ambulance transportation , use of icu and/or ecu , and underlying diseases ( comorbidities ) before and/or during hospitalization , focusing on diabetes mellitus and infectious diseases . among these factors , causative factors for prolongation of hospitalization ( group ii ) were evaluated by multiple logistic regression analysis . all procedures performed in this study were approved by the ethical committee of saga university hospital ( 2015 - 05 - 05 ) . in the statistical analysis , chi square test or mann  whitney u test was used for comparison between the two groups , and p<0.05 was used for significant difference . multiple logistic regression analysis was conducted , with prolonged number of hospital days and onset of infection during hospitalization as objective variables . table  1 shows the baseline characteristics of the patients hospitalized in saga university hospital in the dpc system . as indicated in table  2 , the mortality rate during hospitalization was 1.0% , i.e. , 215 of 20,876 patients . the number of patients transported by ambulance was 2,724 ( 13.1% ) , and the number requiring emergency hospitalization was 3,008 ( 14.4% ) . in total , 2,534 patients ( 12.1% ) had diabetes mellitus , while 765 patients ( 3.7% ) had infectious diseases at admission and 502 patients ( 2.4% ) during hospitalization . the number of patients categorized into group ii ( hospitalization days beyond period 3 ) was 2,356 of 20,876 ( 11.3% ) . table  3 shows causative factors for prolongation of hospitalization days beyond period 3 evaluated by univariate analysis . aging but not gender was a risk factor for long hospitalization . mortality was high in group ii compared with group i ( p  =  0.020 ) . setting days of period 3 in each dpc influenced categorization of group ii , indicating that dpc code with short setting dpc days was significantly higher when classified into group ii ( p<0.001 ) . ambulance transportation and unplanned ( emergency ) hospitalization did not prolong hospitalization days . compared with group i , the patients in group ii were more likely to occupy beds for general patients and icu , but not ecu . comorbidity of infectious diseases at admission was not a risk factor for prolongation of hospitalization , whereas comorbidities of diabetes mellitus and infectious diseases during hospitalization significantly prolonged hospitalization days ( p<0.001 for each ) . causative factors for long hospitalization ( group ii ) analyzed by multivariate analysis are indicated in table  4 . age , short setting period in dpc days , and days spent in icu were risk factors for prolonged hospitalization . regarding comorbidities , diabetes mellitus and infection diseases during the hospital stay were risk factors for long hospitalization . table  5 shows risk factors for contracting infectious diseases during hospitalization evaluated by univariate analysis . these were aging , long setting days of period 3 in each dpc , high mortality rate , ambulance transportation , unplanned hospitalization , long periods of using beds for general patients , ecu , and icu , and comorbidity of diabetes mellitus and infectious diseases at admission . as indicated in table  6 , multivariate analysis showed that significant risk factors for suffering from infectious diseases during hospitalization were aging , dpc code with long setting days of period 3 , days in icu , and comorbid diabetes mellitus . the present study clearly demonstrated that the main causative factors for prolongation of hospitalization in an acute and intensive care hospital in japan were : i ) contracting infectious disease during hospitalization ; ii ) aging ; iii ) comorbid diabetes mellitus ; and iv ) a long stay in icu . infectious diseases during hospitalization were caused by several factors including nosocomial infection and infection following intensive intervention including surgery . the results of the present study suggest that infectious disease complications during hospitalization were linked to increased severity of the patient s illness . this was demonstrated by the higher mortality rate in group ii ( the prolonged hospitalization group ) of 1.49% , which was significantly higher than in group i ( 0.97% ) . however , the present study did not examine in detail the causes of mortality and/or infectious diseases during hospitalization because of ethical limitations , and these areas warrant further exploration . aging and diabetes mellitus , which might exacerbate infectious diseases , were also risk factors for prolongation of hospitalization . regulation and control of infectious diseases during hospitalization has been enforced by the infectious diseases control division in the hospital , and the present study clearly demonstrated the importance of infectious disease control during hospitalization . in contrast to infectious diseases during hospitalization , infectious diseases at admission were not a risk factor for long hospitalization . this might be because treating these diseases was the main purpose of hospitalization , and/or that control of these comorbidities was relatively achieved before admission for therapeutic intervention . this study indicated that diabetes mellitus and aging were risk factors for infection during hospitalization , which suggests that careful medical support is required for these patients during hospitalization . the results of the present study showed that long duration in icu was equivalent to long hospitalization , indicating that speedy movement from icu to general beds , with appropriate therapeutic intervention , was required for quick discharge , in turn leading to improved prognosis for these patients . regarding setting days of period 3 in each dpc , this study revealed two results : i ) the setting days of period 3 was shorter in group ii compared with group i , and ii ) setting days of period 3 was longer in the patients with infectious diseases during hospitalization . the first result suggests that setting days may be re - evaluated in several dpc codes , while the second indicates that setting days of dpc was appropriately long in severe diseases with infection during hospitalization . in conclusion , this relatively large study with 20,876 patients indicated that the most important factor for reducing hospitalization days was to prevent infection during hospitalization especially for aged and/or diabetes mellitus patients . rapid removal from icu with appropriate therapeutic approaches might be also important for reducing hospitalization days . principal investigator , data collection , statistical analysis , and manuscript preparation : susumu fujii . data collection : shinichiro ishikawa , yosuke aoki , keizo anzai , shigeki morita , kazuma fujimoto , and masaaki mawatari .
this study aimed to evaluate causative factors for prolonged hospitalization based on hospitalization status , type of hospital ward , and comorbidities , specifically diabetes mellitus and infectious diseases , in 20,876 patients hospitalized in saga university hospital from april 1 , 2012 , to february 28 , 2015 . 
 prolonged hospitalization was defined as hospital days exceeding period 3 in the diagnosis procedure combination system . among all factors , causative ( risk ) factors for prolonged hospitalization 
 were evaluated by multiple logistic regression analysis . 
 multivariate analysis indicated causative factors for prolonged hospitalization were aging , comorbid diabetes mellitus , time spent in the intensive care unit , and infectious diseases contracted during hospitalization . 
 the risk factors for contracting infectious diseases during hospitalization were aging , male sex , comorbid diabetes mellitus , and increased number of days spent in period 3 in the diagnosis procedure combination code . 
 these data indicated that critical factors for discharge from hospital within an appropriate time frame were prevention of infectious diseases during hospitalization , and a fast and effective therapeutic approach to patients in the intensive care unit .