Acute pyelonephritis (AP) represents the most severe form of urinary tract infection (UTI) and is associated with significant morbidity and even mortality. Approximately 250 000 cases of AP occur each year in the US, with the incidence being higher in women than men.1 The aetiological agent is Escherichia coli in around 80% of the cases.2 Acute pyelonephritis has a quoted mortality of 10% to 20%.3 Several studies have identified a number of risk factors for prediction of poor outcome, including urinary tract abnormality, general debility, and properties (ie virulence and resistance profile) of microorganisms.4 5

The aim of this study was to review patient demographics and outcomes of severe AP in a regional hospital, and to identify possible prognostic factors for long hospital stay and fatal events.

We conducted a retrospective medical record review. All patients admitted for AP between June 2007 and June 2012 to Pamela Youde Nethersole Eastern Hospital, Hong Kong were identified. Only patients with the most severe outcomes were analysed consecutively: (1) mortality, (2) need for care in the intensive care unit (ICU), or (3) necessitation of urological intervention. Patients suffering from postoperative pyelonephritis were excluded.

The following data were collected: patient demographics, presence of urinary tract obstruction, presence of septic shock, need for intensive care, modalities of urological intervention, bacteriologies, length of stay, and mortality.

Data analysis was performed by the Statistical Package for the Social Sciences (Windows version 20; SPSS Inc, Chicago [IL], US). A P value of less than 0.05 was regarded as statistically significant. Chi squared test and logistic regression analysis were performed. The independent variables were patients’ demographic and clinical data; the dependent variables were mortality and long hospital stay (>14 days).

A total of 432 patients were admitted for AP from June 2007 to June 2012. Of these, 68 patients fulfilled our inclusion criteria for severe AP. Baseline patient demographics, clinical characteristics, and imaging findings are illustrated in Table 1.6 Overall, 75.0% of the patients (n=51) demonstrated radiological evidence of urinary tract obstruction, secondary to stone (51.0%), ureteral stricture (5.8%), or extrinsic compression (7.2%). Six patients had suppurative renal infections, namely, renal abscess and emphysematous pyelonephritis.

The yields of blood culture were positive in 57.4% of the patients, with E coli being the commonest causative organism (38.2%) followed by Klebsiella pneumoniae, Proteus mirabilis, and Acinetobacter species. Only three patients had bacteraemia caused by extended-spectrum β-lactamase–producing E coli (Table 2).

The prevalence of bacteriuria was 73.5%, and E coli accounted for the majority of cases with bacteriuria, followed by K pneumoniae and Pseudomonas aeruginosa (Table 2).

In addition to antibiotic administration, 75% (n=51) of the patients required urological interventions, including percutaneous nephrostomy (n=41), insertion of ureteric stent (n=5), percutaneous drainage (n=1), and nephrectomy (n=5).

The overall mortality was 7.4% (n=5). Table 3 summarises the characteristics of patients who died due to pyelonephritis within the same admission.

Risk factors for long hospital stay (>14 days; 32.4%) and mortality (7.4%) were analysed (Tables 4 and 5).

Presence of bacteraemia (P=0.022), suppurative pyelonephritis (P=0.005), shock (P=0.016), and need for ICU care (P=0.003) were significant risk factors for long hospital stay on univariate analysis. On multivariate analysis, the odds ratios (ORs) were 3.71 for bacteraemia (P=0.026), 13.23 for suppurative pyelonephritis (P=0.022), 3.65 for shock (P=0.018), and 5.85 for ICU care (P=0.005).

On univariate analysis, age of ≥65 years, male sex, deranged renal function, and disseminated intravascular coagulation (DIC) were predictors for death. However, only male sex (OR=11.75; P=0.033) and DIC (OR=10.31; P=0.018) were shown to be independent risk factors in multivariate regression analysis.

Severe AP is an important disease entity that frequently requires hospitalisation. Early recognition of patients who are at risk of prolonged hospital stay or even fatal events is important to improve treatment results. Previous studies4 5 have shown a number of risk factors including immunosuppression, old age, and diabetes as risk factors for treatment failure. We were interested in finding whether these risk factors also applied to the local Hong Kong population.

An epidemiological study in the US found that women are approximately 5 times more likely than men to be hospitalised for AP; however, women have a lower mortality rate than men.7 In our study of hospitalised patients, females accounted for the majority (70.6%) of AP cases. However, all but one mortality from pyelonephritis occurred in the male patients.

In one study on AP in adults, E coli was the aetiological agent in 80% of the cases, but E coli infections were less common in elderly patients (60%). Furthermore, infections due to P mirabilis, K pneumoniae, Serratia marcescens, and P aeruginosa were very common due to the increased use of catheters.2 Our study showed a similar microbial spectrum. However, in AP, it is not always possible to routinely document clinical UTI. This could be attributed to previous antibiotic treatment, low bacterial growth, or presence of atypical pathogens.8 In the present analysis, it was possible that a certain proportion of patients had received antibiotic treatment before admission to the hospital. Despite this, the prevalence of bacteraemia and bacteriuria was relatively high (57.4% and 73.5%, respectively). Escherichia coli accounted for the majority of causative organisms.

An obstructed and infected kidney is a urological emergency that may progress to septic shock. Since acute obstructive uropathy raises the renal pelvic pressure and, theoretically, decreases the uptake of drugs by the kidney, emergency drainage is warranted. A urological intervention significantly increases the chances of good initial outcome.6 9 In this study, all patients who showed radiological evidence of urinary tract obstruction were treated with emergency drainage.

It has been suggested that bacteriuria and UTI occur more commonly in subjects with diabetes than in the general population, and the risk of upper tract involvement is also increased in these people.10 Diabetes seems to be associated with an increased risk of severe UTI and unusual manifestations.11 12 The prevalence of diabetes in the present study was also high (36.8%). In contrast with the results of several studies, it was not shown to be a risk factor for prolonged hospitalisation.4 5 The initial choice of empirical antimicrobial therapy was not different for diabetic patients, but we were more vigilant for complications of UTI, such as emphysematous pyelonephritis and abscess formation, in this group of patients.

Recent reports4 13 have shown other risk factors such as long-term catheterization and age of >65 years to be predictive of prolonged hospitalisation. Our study revealed that four risk factors—including bacteraemia, shock, need for intensive care, and suppurative pyelonephritis—were associated with long hospital stay. These four risk factors were closely related with and denoted the most severe degree of pyelonephritis, thus resulting in longer hospitalisation.

The mortality rate for patients with pyelonephritis has been reported to be 1.2% to 33%.14 15 In our study, which included more severe group of AP patients (ie those who required intensive care or urological interventions), the overall mortality rate was 7.4%. According to a previous study,4 septic shock, bedridden status, age of >65 years, recent use of antibiotics, and immunosuppression were independent predictors of death. Another research found that baseline health status of patients and complexity of suppuration were the most important predictors of clinical outcomes for suppurative renal infections.6 In our analysis, patients who died due to AP were predominantly older than 65 years, presented with septic shock, and required drainage for urinary tract obstruction. Among the risk factors studied, age of ≥65 years, male sex, deranged renal function, and DIC were associated with mortality in univariate analysis. Additional multivariate correlates were male sex and presence of DIC.

The limitation of the study was that the study population consisted of a heterogeneous group of patients and might not be representative of the majority of uncomplicated AP cases. Presence of resistant pathogens may contribute to treatment failure, but we did not estimate this factor in our analysis. Nevertheless, the outcomes of severe AP also bear clinical implications for physicians who mainly treat critically ill, hospitalised patients.

There was high prevalence of bacteraemia and septic shock in patients with severe AP, with E coli being the predominant causative organism. Male sex and presence of DIC were associated with mortality. Early recognition of risk factors can potentially help prevent death from severe AP.

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