To our knowledge, this work is the first report using CHAID decision tree analysis to perform a direct comparison between patients positive and negative for bacteremia among those with pyelonephritis. Patients with White blood cell > 21,000/µL constituted a quite-high-risk group. Patients with White blood cell ≤ 21,000/µL plus Chill plus Aspartate aminotransferase > 19 IU/L constituted a high-risk group. In contrast, patients with White blood cell ≤ 21,000/µL plus non-Chill plus Albumin > 3.60 g/dL were at low-risk. The AUC for the ROC curve demonstrated acceptable accuracy.
White blood cell counts (WBC), C-reactive protein (CRP) levels and procalcitonin are frequently used as markers of a systemic inflammatory reaction, but CRP and procalcitonin were not incorporated into the model for bacteremia among patients with pyelonephritis in our CHAID decision tree analysis. Several studies have shown the usefulness of CRP for estimating the risk of bacteremia in patients with neutropenia during cancer [20] or in Intensive Care Unit (ICU) patients [21]; in contrast, another study concluded that CRP was not a sensitive or specific marker for bacteremia in patients with signs of sepsis [22]. Indeed, CRP was not detected as a bacteremia factor in our preliminary research [7]. Similarly, as for procalcitonin, a severity judgment of sepsis and the utility in the prognostic value were demonstrated [23]; in contrast, another meta-analysis study concluded that procalcitonin was also not a sensitive or specific marker for bacteremia in patients with signs of sepsis [24] Our study results suggested that the increased WBC count is a timely and reliable response to bacteremia. It is important to consider obtaining blood cultures when patients have a high WBC count, even when the CRP level and procalcitonin are not elevated. Furthermore, hospitalization should be strongly considered with a WBC > 21,000/µL because these patients represented a quite-high-risk group in the present study.
Several studies have shown that the presence of chill is a powerful single predictor of bacteremia [25–29]. In Japanese emergency rooms, it has been reported that the severity of chill correlates with the risk of bacteremia [30, 31]. Separately, increases in AST levels are postulated to reflect rhabdomyolysis associated with the fever and early impairment of circulation. Even if WBC remains below 21000/µL, hospitalization is recommended when patients have Chill and AST > 19 IU/L, given that these patients constituted a high-risk group in the present study.
Another study formulated a predictive model for the mortality of patients with Staphylococcus aureus bacteremia, in which a low serum albumin level was one of the predictors [32]. Similarly, the present study identified serum albumin levels over 3.60 g/dL as a predictor for the low-risk group. Together, these results suggest that nutritional status may contribute to bacteremia and associated outcomes. Furthermore, patients with pyelonephritis who exhibit WBC ≤ 21,000/µL plus non-Chill plus Albumin > 3.60 g/dL constituted a low-risk group in the present study, so it is possible that low-risk-group pyelonephritis patients can be treated on an outpatient basis. However, the CHAID analysis still provides only an index; it remains important that we ascertain the state of each patient carefully and decide on treatments in an informed manner. If a patient’s overall clinical status is poor, hospitalization should be considered.
The quick Sequential Organ Failure Assessment (qSOFA) now is used widely. In out-of-hospital, emergency department, or general hospital ward settings, adult patients with suspected infections can be identified rapidly as being more likely to have poor outcomes typical of sepsis if the patients have at least 2 of the following clinical criteria: respiratory rate of 22/min or greater, altered mentation, or systolic blood pressure of 100 mmHg or less [9]. In the present study, patients with pyelonephritis who presented with qSOFA scores of 2 had a significantly higher percentage of bacteremia (p = 0.04) (Table 2). However, based on the AUC values of the ROC curves shown in Figs. 2 and 3, the model based on the CHAID decision tree analysis (as generated in the present study) exhibited greater power than qSOFA. Thus, CHAID decision analysis was superior to qSOFA in identifying bacteremia-predictive factors among patients with pyelonephritis. In fact, other studies providing comparisons with qSOFA already have been reported [33, 34], and further such studies are expected in the future.
Based on the literature, E. coli is the most frequent cause of pyelonephritis [35]. In this study, E. coli also was the most-frequent causative microorganism. Possible virulence factors of this species include the ability to adhere and colonize the urinary tract, an important initiating factor in all UTIs [35]. Furthermore, in the present study, 13.5% of E. coli isolates (10 of 74 E. coli cases total) were Extended-Spectrum Beta-Lactamase (ESBL) producers. A previous study also showed that ESBL-producing E. coli are increasingly recognized among community-acquired infections [36]. Given that the fraction of ESBL-producing E. coli may increase further in the future, there is an increasing need to exercise care in the choice of medical treatment for pyelonephritis.
There were some limitations to this study. The patient population enrolled in this study was limited to a single hospital. In addition, this research consisted of a retrospective study. As a next step, a multi-center prospective study should be conducted with a larger number of patients.