Routine Antibiotic Prophylaxis Is Not Required for Patients Undergoing Shockwave Lithotripsy: Outcomes from a National Shockwave Lithotripsy Database in New Zealand

Abstract

Purpose:

To assess the effectiveness of routine prophylactic antibiotics in the prevention of urinary tract infection (UTI) after extracorporeal shockwave lithotripsy (SWL) and identify predictors of UTI development in a multicenter series of over 10,000 stone cases treated in New Zealand over a 20-year period.

Materials and Methods:

Patients treated with SWL on the Mobile Medical Technology vehicle between June 19, 1995 and December 1, 2014 were identified. Data collection was undertaken prospectively for patient, stone and treatment characteristics, and, retrospectively, for treatment outcomes. The primary outcome was clinical UTI, defined as development of UTI symptoms requiring antibiotic therapy. Secondary outcomes included urinary sepsis, need for hospital admission due to infectious complications, and length of hospital stay. Multivariate analysis was undertaken to identify factors independently associated with the development of post-SWL UTI.

Results:

Antibiotic prophylaxis was used in 62.1% (n = 6710) of cases. On comparing patients who received prophylactic antibiotics to those in whom antibiotics were withheld, no significant differences were observed in terms of post-SWL UTI (1.1% vs 1.3%, p = 0.335) or urinary sepsis (0.04% vs 0.15%, p = 0.075). The use of prophylactic antibiotics was not independently associated with post-SWL UTI (OR: 1.269, 95% CI: 0.886–1.818, p = 0.194). Female gender, larger stone size, and higher number of delivered shocks were predictive of UTI development, but antibiotic prophylaxis did not appear to offer any benefit in this subgroup.

Conclusions:

Routine antibiotic prophylaxis was not associated with a reduction in clinical UTI after SWL in this cohort of over 10,000 stone cases in New Zealand.

Introduction

Extracorporeal shockwave lithotripsy (SWL) is a well-established, low morbidity management option for urolithiasis.^1,2 Current clinical guidelines recommended SWL as first-line treatment for proximal ureteral stones <10 mm and an equivalent first-line treatment option to endourology for renal stones <20 mm, proximal ureteral stones >10 mm, and distal ureteral stones <10 mm.³ Urinary tract infection (UTI) and urinary sepsis are potential complications of SWL and may be caused by the release of bacteria from the fragmented stone alongside shock wave-induced microtrauma to local tissues.² The reported incidence of post-SWL UTI ranges from 0% to 14.0%,⁴ with bacteriuria occurring in up to 23.5% of cases and urinary sepsis in 1.0% to 2.7%.^2,5

While there is widespread consensus regarding the use of targeted prophylactic antibiotics for patients at increased risk of infectious complications post-SWL, including those with indwelling ureteral stent or nephrostomy or with infection stones,^3,6 the use of routine antibiotic prophylaxis for all patients undergoing SWL remains controversial. Current evidence is largely limited to small trials, which do not use clinically significant outcome measures and were undertaken more than 20 years ago.^{7

–15} The question of the value of routine antibiotic prophylaxis for SWL is of immediate importance in light of a global increase in antibiotic resistance^16,17 and the requirement to provide a cost-effective service for the growing patient population with stone disease.^18
–20 Furthermore, there is a need to identify patient, stone, and treatment factors that are predictive of UTI development following SWL so that antibiotic usage can be tailored to individual patient risk.

The objective of this study was to retrospectively identify the effectiveness of routine prophylactic antibiotics in the prevention of infections after SWL in a national, multicenter series of over 10,000 stone cases treated with the Dornier DoLi-S1 and its sister Dornier DoLi-S2 lithotripter in New Zealand over a 20-year period.

Materials and Methods

Study design, participants, and data collection

In this study, an electronic search of the national SWL database of New Zealand was undertaken to identify patients ≥18 years who had undergone SWL on the Mobile Medical Technology (MMT) vehicle between June 19, 1995 and December 1, 2014 for kidney or ureteral stones. Data on patient demographics, stone and treatment characteristics were collected prospectively from June 19, 1995 by the radiographer involved with the respective patient's treatment. Follow-up was undertaken according to a standardized protocol for all patients who received SWL: data collection for stone treatment outcomes, including post-SWL infections, was undertaken retrospectively by a data retrieval nurse who contacted patients, primary care physicians, and relevant departments within each centre at a median of 4.4 months (IQR:7.6) after SWL.

SWL service provision

The MMT SWL vehicle serves a patient population of 4.4 million across 21 hospitals in 14 cities throughout New Zealand. During the period of study, SWL was delivered by a total of 45 radiographers and 85 urologists using the fixed Dornier DoLi-S1 (June 19, 1995 to September 15, 2005) and its sister model, the Dornier DoLi-S2 (September 27, 2005 to December 1, 2014) (Dornier, Germany). An anesthetist was responsible for the assessment of individual patient's suitability for SWL. The following diagnoses were considered contraindications for treatment: acute UTI, abdominal aortic aneurysm, pregnancy, uncorrected coagulopathy, pelviureteric junction obstruction and ureteral strictures, or the use of a pacemaker.

The MMT SWL service recommends the following:

• Pretreatment urine dipstick analysis and mid-stream sample of urine are performed systematically in all patients

• Patients without sterile urine should be treated with a course of appropriate antibiotics before undergoing SWL

The MMT service considered SWL to be contraindicated where:

• UTI symptoms were present (dysuria, hematuria, fever, back pain, malodorous, or cloudy urine),

• Urine dipstick was positive for leukocytes and nitrites, or

• Urine culture was positive for appropriate organism (>10³ colony-forming units)

Antibiotic prophylaxis was defined as a brief course of antibiotics administered before or at the start of SWL. The clinical indications for antibiotic prophylaxis and the specific antibiotic regimen delivered were selected according to local hospital policy and the preferences of the individual-treating urologist.

Outcomes measurements and statistical analysis

The primary outcome was post-SWL UTI, defined as the development of acute UTI symptoms requiring antibiotic therapy, with or without subsequent microbiological confirmation on urine culture. Secondary outcomes included urinary sepsis, defined as the presence of clinical and microbiological evidence of UTI with signs of systemic inflammation (pyrexia/tachycardia/hypotension/tachypnea) requiring hospital admission and intravenous antibiotics, the need for hospital admission secondary to infectious complications, and subsequent length of hospital stay.

Differences between subgroups were tested by using the Student's t-test for normally distributed variables, Mann–Whitney U test for those with skewed distribution, and chi-squared test for categorical variables. Median values were compared using the independent samples median test. Multivariate analysis in the form of binary logistic regression was undertaken to identify those factors related to patient, stone, and treatment characteristics, which were independently associated with the development of post-SWL UTI. All statistical analyses were performed using SPSS software, version 23.0 (SPPS, Inc., Chicago, IL).

Results

An electronic search of the national database identified 11,841 stone cases (8215 patients) treated with SWL between June 19, 1995 and December 1, 2014 on the MMT vehicle in New Zealand. On exclusion of 1032 stone cases lost to follow-up, 10,809 (7769 patients) were included in the final analysis. 88.2% (n = 9538) of included cases were for first SWL session, and the remaining 11.8% (n = 1271) were retreatment cases for previously unsuccessful SWL.

Figure 1 demonstrates the annual use of antibiotic prophylaxis over the study period. Overall, antibiotic prophylaxis was used in 62.1% (n = 6710) of stone cases. In those patients who received prophylaxis, gentamicin (aminoglycoside) was delivered most commonly (76.6%, n = 5140), followed by cefotaxime (cephalosporin) (8.5%, n = 569) and ceftriaxone (cephalosporin) (7.0%, n = 468). Table 1 describes the demographics and stone and treatment characteristics for patient groups in which antibiotic prophylaxis was delivered or withheld. Patients who received prophylactic antibiotics had significantly larger mean stone size (p < 0.0001) and a higher proportion of ureteral stones (p < 0.0001) than those who did not receive antibiotics, but no significant differences were observed between groups in terms of age, gender, or mean number of delivered shocks.

FIG. 1.

Frequency of prophylactic antibiotic use (gray line) and post-SWL UTI by year. SWL = extracorporeal shockwave lithotripsy; UTI = urinary tract infection.

Table 1.

Patient, Stone and Treatment Characteristics

	Prophylactic antibiotics (n = 6710)	No prophylactic antibiotics (n = 4099)	p
Patient demographics
Mean age (SD) (years)	52.9 (14.6)	52.5 (14.2)	0.158
Gender (male:female, n)	2:1 (4498:2212)	2:1 (2724:1375)	0.535
Stone characteristics
Mean stone size (SD) (mm)	10.1 (5.1)	9.6 (4.7)	<0.0001^*
Stone location
Left:Right, n (%)	3867 (57.6):2843 (42.4)	2297 (56.0):1802 (44.0)	0.105
Renal:Ureteral, n (%)	5255 (78.3):1455 (21.7)	3436 (83.8):663 (16.2)	<0.0001^*
Multiple stones, n (%)	2176 (32.4)	1375 (33.5)	0.231
Retreatment, n (%)	789 (11.8)	482 (11.8)	1.000
SWL characteristics
Mean number of shocks (SD)	3912.3 (1446.2)	3886.0 (1382.1)	0.349
Anesthetic type
General:sedation or epidural, n (%)	3609 (53.8):3101 (46.2)	2120 (51.7): 1979 (48.3)	0.037^*
Year of treatment
(1995–2004):(2005–2014), n (%)	3442 (51.3):3268 (48.7)	2130 (52.0): 1969 (48.0)	0.501

SWL = extracorporeal shockwave lithotripsy.

When considering all included stone cases, symptomatic UTI requiring antibiotic therapy after SWL developed in 1.2% (n = 126), urinary sepsis in 0.1% (n = 9), and the need for hospital admission due to infectious complications in 0.4% (n = 40). Furthermore, the median length of hospital stay for those admitted with post-SWL infectious complications was three nights (range 1–14).

On comparing patients who received prophylactic antibiotics to those in whom antibiotics were withheld, no significant differences were observed in terms of post-SWL UTI (1.1% vs 1.3%, p = 0.335), urinary sepsis (0.04% vs 0.15%, p = 0.075), need for hospital admission due to infectious complications (0.3% vs 0.5%, p = 0.211), or median length of hospital stay for infectious complications (2 nights vs 3 nights, p = 0.785) (Table 2). Figure 1 demonstrates that there was no clear relationship between the annual frequency of post-SWL UTI development and the use of prophylactic antibiotics.

Table 2.

Study Outcomes According to Use of Prophylactic Antibiotics

Outcomes	Prophylactic antibiotics (n = 6710)	No prophylactic antibiotics (n = 4099)	p
Urinary tract infection, n (%)	73 (1.1)	53 (1.3)	0.335
Urinary sepsis, n (%)	3 (0.04)	6 (0.15)	0.075
Hospital admission, n (%)	21 (0.3)	19 (0.5)	0.211
Median hospital stay, nights (IQR)	2 (4)	3 (3)	0.785

IQR = interquartile range.

The use of prophylactic antibiotics was not independently associated with post-SWL UTI (OR: 1.269, 95% CI: 0.886–1.818, p = 0.194) on adjusting for other factors within the multivariate binary logistic regression model (Table 3). However, female gender, larger stone size, and a higher total number of delivered shocks were predictive of post-SWL UTI development. The risk of UTI increased by 5.6% for each 1 mm increase in stone size (OR: 0.944, 95% CI: 0.920–0.969) and by 16.4% for every 1000 additional shocks delivered during SWL (OR: 0.836, 95% CI: 0.734–0.951). In addition, females were 2.3 times more likely than men (OR: 2.281, 95% CI: 1.592–3.267) to develop a post-SWL UTI after adjusting for other factors (Table 3).

Table 3.

Multivariate Analysis for Factors Independently Associated with Post-Extracorporeal Shockwave Lithotripsy Urinary Tract Infection

Variable	Odds ratio (95% CI)	p
Age	1.004 (0.992–1.016)	0.533
Gender
Female vs male	2.281 (1.592–3.267)	<0.0001^*
Stone size	0.944 (0.920–0.969)	<0.0001^*
Stone location
Right vs left	1.218 (0.855–1.736)	0.274
Ureteral vs renal	1.373 (0.900–2.094)	0.142
Multiple stones
Single vs multiple	0.759 (0.525–1.098)	0.143
Retreatment
First treatment vs retreatment	0.792 (0.480–1.306)	0.361
Number of shocks	0.836 (0.734–0.951)	0.007^*
Prophylactic antibiotics
None vs delivered	1.269 (0.886–1.818)	0.194

Subgroup analysis of all females (n = 3587) (i.e., both those who did and did not receive prophylactic antibiotics) according to stone size and total delivered shock waves identified those cases at highest risk; post-SWL UTI developed in 3.0% (38/1283) of women with stones ≥11 mm, compared to 1.3% (29/2304) in women with stones <11 mm, and the highest frequency of UTI was observed for females receiving >5000 shocks for a stone >20 mm (9.8%, 5/51) (Table 4). However, further analysis in this high-risk group of patients (women with stones ≥11 mm) demonstrated that the use of prophylactic antibiotics was still not associated with a significant reduction in post-SWL UTI development; of those high-risk patients who received prophylaxis, 2.5% (21/829) developed UTI vs 3.7% (17/454) (p = 0.231) of high-risk patients with no prophylaxis.

Table 4.

Subgroup Analysis: Frequency of Post-Extracorporeal Shockwave Lithotripsy Urinary Tract Infection Development in Females According to Stone Size and Total Shocks Delivered

	<5	5–10	11–20	>20	Total (n)
Total shocks delivered
<3000	2.0 (2/100)	0.7 (3/432)	2.7 (4/148)	0 (0/10)	690
3000–4000	0.8 (1/124)	1.0 (10/975)	1.4 (6/430)	4.7 (2/43)	1572
4001–5000	0 (0/29)	2.4 (9/373)	2.9 (8/273)	4.8 (2/42)	717
>5000	0 (0/18)	1.6 (4/253)	3.8 (11/286)	9.8 (5/51)	608
Total (n)	271	2033	1137	146	3587

UTI = urinary tract infection.

In addition, subgroup analysis undertaken for the whole cohort demonstrated that those patients who received ceftriaxone (n = 468) demonstrated the lowest frequency of post-SWL UTI (0.4%) compared to cases in which gentamicin (1.1%) or cefotaxime (1.9%) was used (Table 5). On inclusion of ceftriaxone prophylaxis within the binary logistic regression model, however, no independent association was seen with its use and post-SWL UTI outcome (OR: 2.921, 95% CI: 0.710–12.011, p = 0.137).

Table 5.

Post-Extracorporeal Shockwave Lithotripsy Urinary Tract Infection Frequency According to Antibiotic Type

Prophylactic antibiotic	Antibiotic frequency, n (%)	Post-SWL UTI frequency (%)
None	4099 (37.9)	53 (1.3)
Delivered (all antibiotics)	6710 (62.1)	73 (1.1)
Gentamicin	5140 (47.6)	56 (1.1)
Cefotaxime	569 (5.3)	11 (1.9)
Ceftriaxone	468 (4.3)	2 (0.4)
Other^*	140 (1.3)	1 (0.7)
Unknown	393 (3.6)	3 (0.8)

Co-amoxiclav (n = 65), cefoxitin (n = 64), trimethoprim (n = 4), penicillin (n = 3), norfloxacin (n = 3), co-trimoxazole (n = 1).

Discussion

The appropriate use of prophylactic antibiotics in urologic procedures represents an issue of increasing importance in light of growing antibiotic resistance globally.^16,17 This study has identified that the routine use of prophylactic antibiotics was not associated with a significant reduction in the frequency of post-SWL clinical UTI in more than 10,000 stone cases in New Zealand over a 20-year period. To the best of the authors' knowledge, this represents the largest reported series examining the use of prophylactic antibiotics in SWL.

The development of symptomatic UTI requiring antibiotic therapy (1.2%) and urinary sepsis requiring hospitalization (0.1%) was a rare complication of SWL in this cohort. A recent prospective study of 526 patients receiving targeted prophylactic antibiotics for SWL²¹ also demonstrated a low frequency of post SWL UTI: only one patient (0.3%) developed a UTI and no (0%) patient developed urinary sepsis. These findings should be interpreted within the context of epidemiological studies demonstrating an annual UTI incidence of 10.8% in women over 18 years in the United States²²; such high levels of background UTI in the wider patient population mean that it may be difficult to attribute post-SWL UTI directly to SWL therapy, but also highlight the relatively limited overall clinical burden imposed by post-SWL infections.

The use of routine prophylactic antibiotics appeared to offer no benefit in the prevention of post-SWL infection. This was demonstrated in both the multivariate model where, on adjusting for age, gender, and stone size, there was no significant association demonstrated between antibiotic usage and the development of post-SWL UTI, and in the univariate analysis where there was no significant difference in UTI frequency observed between those who received and did not receive prophylaxis (1.1% vs 1.3%, p = 0.335). Furthermore, the annual frequency of post-SWL UTI remained consistent despite significant variation in the annual use of prophylactic antibiotics. This offers substantial weight to existing evidence, which suggests routine antibiotic prophylaxis is not required for SWL,^4,21,23 and contradicts the findings of a previous meta-analysis undertaken by Pearle and Roehrborn, which observed a 3.6% decrease in UTI rate with antibiotic prophylaxis.¹⁵ Indeed, the limitations of Pearle's meta-analysis have been well documented, with the inclusion of trials examining antibiotic treatment rather than prophylaxis and the use of bacteriuria as an outcome measure.⁴ Moreover, the infrequency of post-SWL infection in our cohort indicates that even if antibiotic prophylaxis had proven to be effective in the prevention of post-SWL infection, its routine use in all patients may still not represent a more cost-effective option than treatment.

Female patients with larger stones who received a high number of shocks were identified to be at the highest risk for developing UTI after SWL. Although prophylactic antibiotics appeared to reduce the incidence of UTI in such patients (2.5% in prophylaxis group vs 3.7% in no prophylaxis), this did not reach statistical significance. This analysis does not, therefore, provide sufficient evidence for the recommendation of prophylactic antibiotic usage in this subgroup, but should be used to counsel such patients on the associated increased risk of post-SWL UTI development. Further adequately powered studies are required to prospectively assess the effectiveness of prophylactic antibiotic regimens in this high-risk group.

In contrast to the results of previous studies, which have assessed the risk factors for UTI development, this study did not identify any significant independent association between increasing age and post-SWL UTI development.^24,25

The observed discrepancy between the use of prophylactic antibiotics for the majority of patients undergoing SWL during the study period (62.1% overall), and current recommendations of only targeted use in international EAU and American Urological Association (AU) guidelines,^3,6 have important implications for future practice in New Zealand, but is also likely to reflect more widespread inappropriate use of prophylactic antibiotics.²³ A recent questionnaire study of SWL practice in the United Kingdom conducted by Sharma et al. identified that 25% (5/20) of included UK SWL centers currently use antibiotic prophylaxis routinely in all patients.²⁶

The retrospective, observational nature of this study meant that it was not possible to include other unavailable data on other UTI risk factors, such as UTI history or stone composition, including struvite stones, duration of procedure, the presence of stone obstruction and cystoscopy or in-situ ureteral or nephrostomy tubes in the multivariate model,^27,28 or to account for variations in hospital protocols and individual practices in antibiotic prescription between centers in New Zealand. The absence of this data meant that it was not possible to adjust for these potential confounding factors and introduced a potential source of selection bias into our analyses.

However, the retrospective nature of this study facilitated the collection of national data for a very large patient cohort that would have been difficult to achieve within a clinical trial setting. Furthermore, while a median follow-up at 4.4 months for data on clinical UTI development may have been later required, it was a strength of this study that data were collected from hospital departments, primary care physicians, and patients according to a nationally applied protocol by a trained research nurse and centralized to the MMT headquarters in Christchurch.

In addition, our choice of UTI definition to include those who received antibiotic treatment for acute symptoms without the microbiological confirmation of positive urine culture meant that the frequency of post-SWL infection may have been overestimated. However, it was selected on the basis that it reflects daily clinical practice where empirical antibiotic therapy is used for patients in whom there is strong clinical suspicion of UTI, and waiting for the urine culture result before commencing therapy is often impractical. Furthermore, the baseline differences in characteristics observed between those who received antibiotic prophylaxis and those in whom it was withheld does limit the strength of any conclusions that can be drawn from the simple comparative analysis of outcomes between groups. However, we were able to take account of this through the use of the multivariate model in which other covariates were adjusted for, including stone size and location.

Conclusions

This study has examined the use of prophylactic antibiotics in a national, multicenter series of more than 10,000 stone cases undergoing SWL in New Zealand over a 20-year period. The study offers unique data on infection risk and the predictors of infection after SWL to inform future evidence-based guidelines. Routine antibiotic prophylaxis was not associated with a reduction in clinical UTI after SWL in this cohort.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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