Of the 124 694 hospitalizations, 72.97% corresponded to patients aged 0–1 year of age, and 57.49% to female patients. Unspecified UTI and pyelonephritis were more frequent in children aged 0–1 year and cystitis in children aged 2–6 years. Comorbidities accounted for less than 1% of each pathology. Neoplasia was the most frequent comorbidity (0.54%), followed by renal failure (0.13%), diabetes mellitus (0.09%) and vesicoureteral reflux (0.01%). The median length of stay was 5 days (IQR, 3−6). The median cost was 2272 euros (IQR, 1658−3078), with the highest costs corresponding to pyelonephritis and unspecified UTI. Table 1 presents the characteristics of the patients, overall and by disease.

The crude rate of hospitalization due to UTIs in the 2000–2015 period ranged from 1.24 in 2000 to 0.98 in 2015. The rates were higher in female versus male patients in every age group except children aged 0–1 year (Fig. 2). In addition, when we analysed hospitalization rates by age group, we found the highest rates in the 0–1 year group, which also exhibited the greatest overall decrease in hospitalization rates of all age groups over the study period (Table 2).

Figure 2.

Rate of hospitalization due to UTI per 1000 inhabitants by sex (2000–2015). a) Age 0–1 year. b) Age 2–6 years, 7–10 years and 11–14 years.

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As regards the different types of UTI, we found a decreasing trend in the hospitalization rate for each of them. In the case of unspecified UTIs, the rate per 1000 inhabitants decreased from 0.74 in 2000 to 0.62 in 2015. When it came to hospitalizations related to cystitis, the rate per 1000 inhabitants decreased from 0.01 in 2000 to 0.003 in 2015, while the rate of hospitalization related to pyelonephritis decreased from 0.48 in year 2000 to 0.35 in 2015 (online supplemental material 2).

Joinpoint regression analysis showed an AAPC of −1.5% in the frequency of hospitalization due to UTI (95% confidence interval [CI], −2.4 to −0.6). We observed 3 changes in the trend: a 1.8% increase between 2000 and 2004 (95% CI, −0.4 to 4.1), a −6.0% decrease between 2004 and 2009 (95% CI, −8.1 to −4.0) and a 0.3% increase between 2009 and 2015 (95% CI, −0.9 to 1.6) (online supplemental material 3).

When it came to the types of infection, we found changing trends in hospitalizations related to unspecified UTI (Fig. 3) and related to pyelonephritis (Fig. 4). The APC for hospitalizations due to unspecified UTI was 3.7% between 2000 and 2003 (95% CI, −0.1 to 7.6), −5.2% between 2003 and 2010 (95% CI, −6.3 to −4.0) and 2.5% between 2010 and 2015 (95% CI, 0.7–4.2). On the other hand, the APC for hospitalizations due to pyelonephritis was 1.3% between 2000 and 2005 (95% CI, −0.6 to 3.3), −7.9% between 2005 and 2008 (95% CI, −15.5 to 0.3) and −1.5% between 2008 and 2015 (95% CI, −2.7 to −0.3). However, when it came to cystitis-related hospitalizations, we did not find any join points in the trend observed during the study period (Fig. 5) (online supplemental material 3).

Figure 3.

Rates of hospitalization due to unspecified UTI per 1000 inhabitants (2000–2015). a) Age 0–1 year. b) Age 2–6 years, 7–10 years and 11–14 years.

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Figure 4.

Rates of hospitalization due to pyelonephritis per 1000 inhabitants (2000–2015). a) Age 0–1 year. b) Age 2–6 years, 7–10 years and 11–14 years.

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Figure 5.

Rate of hospitalization due to cystitis per 1000 inhabitants (2000–2015). a) Age 0–1 year. b) Age 2–6 years, 7–10 years and 11–14 years.

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The joinpoint analysis in which we used age-adjusted rates showed a decrease in the frequency of hospitalization due to UTI in both male and female patients, which was greater and only statistically significant in female patients (Fig. 2). The AAPC between 2000 and 2015 was −0.7% in male patients (95% CI, −1.5 to 0.0) and −1.8% in female patients (95% CI, −2.5 to −1.0) (online supplemental material 3).

When it came to the hospitalization rate for unspecified UTI, the AAPC from 2000 to 2015 was −0.5% in male patients (95% CI, −1.7 to 0.7) and −1.3% in female patients (95% CI, −2.2 to −0.4), and was only statistically significant in the latter (Fig. 3) (online supplemental material 3).

As for pyelonephritis-related hospitalizations, we also found a decreasing trend in patients of both sexes that was only significant in female patients (Fig. 4) (supplemental material 3). The AAPC from 2000 to 2015 was −1.3 in male patients (95% CI, −2.9 to 0.4) and −2.2%, a significant decreasing trend, in female patients (95% CI, −3.3 to −1.1).

In cystitis-related hospitalizations, the decreasing trend was statistically significant in patients of both sexes (Fig. 5) (supplemental material 3). The AAPC from 2000 to 2015 was −5.3% in male patients (95% CI, −8.8 to  −1.6) and −7.5% in female patients (95% CI, −9.3 to −5.7).

In the period under study, we found the greatest decrease in the rate of hospitalization due to UTIs in children aged 7–10 years, with an AAPC of −5.9% (95% CI, −6.7 to −5.2). The decreasing trends corresponded to AAPCs of −0.3% in the 0–1 year age group (95% CI − 1.1 to 0.4), −0.3% in the 2–6 years group (95% CI, −1.1 to 0.4), −3.0% in the 7–10 years group (95% CI, −4.0 to −2.0) and −2.9% in the 11–14 years group (95% CI, −3.8 to −2.0). All the decreases were statistically significant except in the 0–1 year age group (online supplemental material 4).

Throughout the study period, the trends in hospitalization due to unspecified UTIs in different age groups were very similar, with a decreasing trend of −0.9% (AAPC − 0.2% in children aged 0−1 years [95% CI, −1.2 to 0.8], −2.4% in children aged 2−6 years [95% CI, −4.0 to −0.7], −5.8% in children aged 7−10 years [95% CI, −6.7 to −4.8] and −4.3% in children aged 11−14 years [95% CI, −5.6 to −3.0]), and the decrease was statistically significant in every age group except children aged 0–1 year (Fig. 3). The analysis identified 2 join points in the trends of hospitalization due to unspecified UTI in the 0-to-1 and 2-to-6 year age groups (in 2003 and 2010 and in 2002 and 2012, respectively) (supplemental material 4).

The trends by age group in hospitalization due to pyelonephritis were very similar, with a decreasing trend of −1.9% (AAPC of −0.4% in children aged 0−1 years [95% CI, −2.0; 1.2], −3.1% in children aged 2−6 years [95% CI, −4.9 to −1.3], −6.0% in children aged 7−10 years [95% CI, −6.8 to −5.1] and −0.7% in children aged 11−14 years [95% CI, −3.7 to 2.3]), changes that were statistically significant only in the 2-to-6 and 7-to-10 year age groups (Fig. 4). The analysis of the trends of hospitalization due to pyelonephritis identified 2 join points in the 0-to-1 and 2-to-6-year age groups (in 2004 and 2008 and in 2005 and 2008, respectively) (online supplemental material 4).

The trends by age group in hospitalization due to cystitis were very similar, with a decreasing trend of −6.9% (Fig. 5). The AAPCs from 2000 to 2015 were −4.5% in children aged 0–1 year (95% CI, −8.2 to −0.6), −8.0% in children aged 2–6 years (95% CI, −11.0 to −4.8) and −7.7% in children aged 7–10 years (95% CI − 9.5 to −5.8) with statistically significant changes in all 3 age groups. There were no AAPC data for the group aged 11–14 years (online supplemental material 4).

In the 2000–2015 period, there were 124 694 recorded hospitalizations in children under 15 years of age, and we found a decrease in the hospitalization rate due UTIs, overall and for each type of UTI under consideration. Children aged 0–1 year were the age group with the highest hospitalization rate. Different guidelines on the management of UTI management in children under 2 years published throughout the study period agree on the criteria for hospitalization due to UTIs in children: age less than 2 or 3 months, presence of urinary system malformations or impaired renal function, septic appearance or dehydration (suspected or laboratory-confirmed), and intolerance of oral route of drug administration or lack of response to oral antibiotics within 48 h.25,26

In our study, the rate of hospitalization due to UTI was higher in female versus male patients than males through nearly the entire study period, except in the 0-to-1 year age group, in which the hospitalization rate was similar for both sexes during several periods.6 This finding is in agreement with other studies that found an increased incidence of UTIs in uncircumcised boys in the first year of life due to an increased risk of infection from foreskin contamination.4,6,27

The crude hospitalization rate decreased over time for all types of UTIs, with the most significant trend change taking place between 2003 and 2010. This trend is similar to what has been described in other countries, such as the United States,28 where a decrease in hospitalizations for UTIs has also been observed since 2003, although it was only statistically significant in the 2009–2012 period. This decrease in hospital admissions may be due to multiple causes, including changes in its management and a decrease in the incidence of ITUs.

In recent decades, febrile UTIs in children have been generally managed at the inpatient level. This practice is founded on the assumption that early intravenous antibiotic treatment offers an advantage in terms of rapid infection control. Since 1999, different clinical trials have demonstrated that oral antibiotic treatment of children with febrile UTIs is as effective as intravenous treatment in terms of clinical and bacteriological control of the infection29 and that oral and intravenous antibiotherapy is equally effective for treatment of pyelonephritis in children aged more than 1 month,30 leading to the recommendation of administering oral antibiotherapy between ages 1 and 24 months. Later, in 2011, the American Academy of Pediatrics included these recommendations in its guideline, thus reducing the number of cases in which the use of antibiotics delivered parenterally would be recommended.25 The same year, these recommendations were also included in the guidelines published by the Ministry of Health of Spain.31 Based on this evidence, the recommendation in favour of hospital admission for the management of paediatric patients with febrile UTIs has been restricted. The availability of a much less aggressive route of administration, such as the oral route, which allows outpatient treatment, is one of the causes that may explain the decreased rate of hospitalization observed in the study period. This directly affected children under 2 years, who were the target population of the updated recommendation but also probably, although to a lesser extent, all other age groups, by promoting the treatment of UTIs at the outpatient level.28 The authors of the study conducted in the United States after the changes made in 2011 proposed the same hypothesis to explain the greatest decrease in hospital admissions, observed in the oldest age group (15–17 years).

Another reason for the decreased hospitalization rate is the decreased incidence of UTIs, resulting from the change in diagnostic criteria, which have become more restrictive, and from improved prenatal diagnosis of urinary anomalies. In 2009, the diagnosis of UTI was based on a positive urine culture.7 Similarly, it is possible that improved prenatal detection of urinary anomalies and earlier detection of vesicoureteral reflux (VUR) have led to a decrease in UTIs in the paediatric population. In these cases, which carry a high risk of infection, antibiotic prophylaxis can be initiated early, which may have contributed to the decrease in UTIs in this group of patients. In our series, there were very few children with VUR.

From an epidemiological point of view, VUR is an important cause of UTI, although it is only an indication for hospital admission in the most severe cases (grades IV-V),1 a fact that may partly justify the low frequency of UTI associated with VUR in our study. We should also bear in mind potential documentation issues that may arise from the particular features of the CMBD database.

The CMBD is a secondary data source, and its quality may be conditioned by the quality of the hospital discharge reports and the accuracy of the coding, which can vary among health care facilities. However, the coding process has improved markedly since 2001, and the CMBD registry is considered valid for epidemiological studies such as this one. A limitation derived from the CMBD is that it does not allow identifying the type of treatment received by the patient or recurrent readmissions, as readmissions are only recorded in the first 30 days after discharge. As regards comorbidities, the CMDB allows a maximum of 14 diagnoses per patient (one main diagnosis and 13 secondary diagnoses). We do not expect that this limit would result in missing information in the paediatric age group.

We consider that the results obtained in this study are representative of hospitalizations for UTIs in Spain and show the temporal trends of UTIs at the national level over a period of 16 years, allowing an estimate of the burden of this disease in children aged less than 15 years and its impact on the national health system.