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This is infection within the renal pelvis, usually accompanied by infection within the renal parenchyma. The source of sepsis is often ascending infection from the bladder but haematogenous spread can also occur. The usual organisms are the same as for lower urinary tract infection (UTI) - eg, Escherichia coli, Klebsiella spp., Proteus spp., Enterococcus spp. Unusual organisms are occasionally seen - eg, mycobacteria, yeasts and fungi and opportunistic pathogens such as Corynebacterium urealyticum. Repeated attacks of acute pyelonephritis can lead to chronic pyelonephritis.
Acute pyelonephritis can occur at any age. In neonates it is 1.5 times more common in boys and tends to be associated with abnormalities of the renal tract. Uncircumcised boys tend to have a higher incidence than circumcised boys. Beyond the age of a year, girls have a higher incidence than boys. In adult life it reflects the incidence of UTI in that it is much more common in young women. Over the age of 65 the incidence in men rises to match that of women.
- Structural renal abnormalities
- Calculi and urinary tract catheterisation
- Stents or drainage procedures
- Primary biliary cirrhosis
- Immunocompromised patients
- Neuropathic bladder
Onset is usually rapid with symptoms appearing over a day or two. There is unilateral or bilateral loin pain, suprapubic or back pain. Fever is variable but can be high enough to produce rigors. Malaise, nausea, vomiting, anorexia and occasionally diarrhoea occur. There may or may not be accompanying lower urinary tract symptoms with frequency, dysuria, gross haematuria or hesitancy. Gross haematuria occurs in 30-40% of young women. The patient looks ill and there is commonly pain on firm palpation of one or both kidneys and moderate suprapubic tenderness without guarding.
Presentation in children, especially when young, can be much less specific and culture of urine should be a routine investigation in pyrexial and unwell infants.
- Abdominal abscess
- Abdominal aortic aneurysm
- Causes of acute abdomen
- Causes of loin pain
- Ectopic pregnancy
- Interstitial cystitis
- Papillary necrosis
- Pelvic inflammatory disease
- Renal corticomedullary abscess
- Renal vein thrombosis
- Sexually transmitted infections
- Ureteropelvic junction obstruction
- Vesicoureteral reflux
- Vesicovaginal and ureterovaginal fistula
- Urinalysis: the urine is often cloudy with an offensive smell. It may be positive on dipstick urinalysis for blood, protein, leukocyte esterase and nitrite. A midstream specimen of urine (MSU) should be sent off for microscopy and culture, although there is often poor correlation between symptoms and bacteriuria. A catheter specimen will be acceptable if a catheter is in situ and special arrangements may be needed for collecting a sample from a child (eg, peroneal bag, suprapubic aspiration). Microscopy of urine shows pyuria.
- Inflammatory markers: CRP, ESR, and plasma viscosity are raised.
- Recent studies identified procalcitonin as a biological marker in diagnosing acute pyelonephritis in children of 2 years of age or under.
- FBC: this shows elevated white cell count with neutrophilia.
- Blood cultures: these are positive in approximately 12-20% of patients with pyelonephritis.
- Imaging is useful if the clinical picture or biochemical markers are ambivalent, as structural problems are not uncommon. It is recommended for all, but is mandatory in patients with recurrent pyelonephritis and may help to identify obstruction or stones.
- Contrast-enhanced helical/spiral CT (CECT) scan is the best investigation in adults where diagnosis is in doubt or deterioration occurs. Non-contrast helical/spiral CT scans will pick up moderate to severe disease but may be normal in milder cases.
- In children, the choice is between ultrasound and CT scanning. CT is more sensitive but the exposure to radiation may make ultrasound a safer option.
- Dimercaptosuccinic acid (DMSA) scan is mainly used for detailed renal cortical views in recurrent cases, to detect scarring..
- MRI is also useful in detecting scarring but may require sedation in children. In adults, it is increasingly used where renal infection, masses and urinary obstruction are suspected but its use is limited by cost and availability.
- Renal biopsy is occasionally employed to exclude papillary necrosis.
- The Fairley test: is worth mentioning for historical interest, as it is still referred to in the literature; however, it is rarely used today because it is labour-intensive and involves introducing a Fairley catheter into an already infected urinary system. The objective is to determine whether infection is confined to the bladder or has spread to the kidneys. A bladder washout with neomycin and fibrinolytic enzymes is performed. Then a urine culture is taken immediately and at 10, 20 and 30 minutes. With isolated bladder infection, bacteriuria returns slowly. With kidney infection, bacteriuria appears rapidly.
- Support: rest, adequate fluid intake and analgesia are important.
- Hospital admission: many patients can be managed in the community, providing they are otherwise healthy. Guidelines generally recommend admission for pregnant women, although the few randomised trials which exist suggest that outpatient treatment is safe. Indications for admission include:
- Severe vomiting
- Comorbidity such as diabetes
- Signs of sepsis (eg, tachypnoea, tachycardia, hypotension)
- Severe pain or debility
- Failure of response to treatment in primary care
- Urinary tract obstruction
- Oliguria or anuria
- Suspected complications (see 'Complications', below)
- Uncertain diagnosis
- Social issues
- Non-concordance with treatment
- Inadequate access to follow-up
- Relapse of symptoms as soon as antibiotics have been stopped
- Antibiotics: start empirical antibiotic treatment whilst awaiting culture and sensitivity. For adults, ciprofloxacin for seven to ten days (adult dose 250-500 mg PO bd). A third-generation cephalosporin (eg, ceftibuten) could be an alternative, but co-amoxiclav is not recommended for empirical treatment. Local protocols may suggest other antibiotics and should be followed, as resistance patterns may vary.
There is a theoretical concern that children who are not treated with early intravenous antibiotics could develop renal scarring. However, studies suggest that most cases in children can be managed with oral therapy.
- Surgery: this may be required to drain renal or perinephric abscesses, or to relieve obstructions causing the infection (eg, stones).
These occur more often in patients with diabetes mellitus, chronic renal failure, sickle cell disease, renal transplant (especially the first three months), AIDS and other immunocompromised states. They include:
- Perinephric abscess (more common if there is urinary tract abnormality).
- Renal abscess, including emphysematous pyelonephritis (rare, life-threatening form with tissue necrosis and accumulation of gas in the renal parenchyma, perinephric space and collecting systems - particularly occurs in obese, elderly diabetic women with urinary tract obstruction).
- Acute papillary necrosis, which is more likely in the elderly and those with diabetes (suggested by associated symptoms of renal colic).
- Pregnancy - tends to produce a more complicated course with significant risk of premature labour.
- Pyelonephritis, which is more likely to scar the kidney of a growing child.
Premature labour can occur in pregnant women. Most other patients have an uncomplicated recovery, providing there are no significant comorbidities.
Consider prophylactic treatment in women with at least three symptomatic infections a year. Trimethoprim is widely used. In children, the current approach is to reserve antibiotic prophylaxis for those who are at highest risk of complications (eg, demonstrable vesicoureteric reflux, recurrent infections or renal scarring on imaging).
This produces characteristic scarring on the kidney and occurs after recurrent or persistent infections.
A UK study found an increase in incidence in the Indo-Asian immigrant community, possibly associated with tuberculosis. The prevalence has been quoted as four out of 100,000 asymptomatic adults.
- Any structural renal tract anomalies, obstruction or calculi
- Children with vesicoureteral reflux
- Intrarenal reflux in neonates
- Genetic predisposition
- Any factors predisposing to recurrent urinary infection - eg, neurogenic bladder
- Loin pain
- Failure to thrive
- Urine microscopy, culture and sensitivity: this may be helpful in identifying the organism involved but negative urine culture does not exclude diagnosis.
- Intravenous pyelogram (IVP) may show small kidneys, ureteric and caliceal dilatation/blunting with cortical scarring.
- Voiding cystourethrogram (VCUG) may help to identify reflux.
- Ultrasound and KUB X-ray may show stones but are not sensitive for reflux nephropathy.
- Technetium-99m Tc-DMSA scan may show renal scars. One study reported that power Doppler ultrasonography was an alternative option in children.
- Blood pressure should be controlled to slow the progression of renal failure. Ideally angiotensin-converting enzyme (ACE) inhibitors should be used.
- Supervening UTI may require lengthier courses of antibiotics than are normally given.
- Severe underlying vesicoureteral reflux diagnosed in children may require antibiotics prophylactically until puberty or until the reflux resolves (see 'Prevention', below).
- Surgical re-implantation of the ureters may be needed in severe cases but, in most cases, surgical management is not superior to medical.
- Renal failure may eventually require renal transplantation.
- Progressive renal scarring with reflux nephropathy and renal failure
- Secondary hypertension
- Focal glomerulosclerosis
- Urea-splitting organisms can lead to staghorn calculi - the usual culprit is Proteus spp.
One study found that 25% of children with vesicoureteral reflux developed chronic renal failure. 29% of the sample eventually developed hypertension. Adults with chronic pyelonephritis generally have good prognosis with preserved renal function.
- On the assumption that most pyelonephritis is caused by ascending infection, its prevention is based on preventing UTI. If children have structural abnormalities of the renal tract they require assessment with a view to correction.
- In those with severe vesicoureteric reflux, long-term antibiotics may be of benefit but there is no evidence that they are beneficial in mild reflux.
- The evidence supporting the preventive benefits of cranberry juice is equivocal and further large-scale trials are needed.
- Women should be encouraged to void after sexual intercourse.
- A Cochrane review concluded that antibiotic treatment of asymptomatic bacteriuria of pregnancy does reduce the risk of pyelonephritis.
Further reading & references
- Saadeh SA, Mattoo TK; Managing urinary tract infections. Pediatr Nephrol. 2011 Nov;26(11):1967-76. Epub 2011 Mar 16.
- Pyelonephritis - acute, NICE CKS, March 2009
- Sheu JN, Chang HM, Chen SM, et al; The role of procalcitonin for acute pyelonephritis and subsequent renal scarring J Urol. 2011 Nov;186(5):2002-8. Epub 2011 Sep 23.
- Chen KC, Hung SW, Seow VK, et al; The role of emergency ultrasound for evaluating acute pyelonephritis in the ED. Am J Emerg Med. 2011 Sep;29(7):721-4. Epub 2010 May 1.
- Giroux J, Perkash I; Limited value of the Fairley test in urologic infections in patients with neuropathic bladders. J Am Paraplegia Soc. 1985 Jan;8(1):10-2.
- Management of suspected bacterial urinary tract infection in adults; Scottish Intercollegiate Guidelines Network - SIGN (updated guidelines 2012)
- Guidelines on Urological Infections; European Association of Urology (Mar 2013)
- Bocquet N, Sergent Alaoui A, Jais JP, et al; Randomized trial of oral versus sequential IV/oral antibiotic for acute Pediatrics. 2012 Feb;129(2):e269-75. Epub 2012 Jan 30.
- Nickavar A, Sotoudeh K; Treatment and prophylaxis in pediatric urinary tract infection. Int J Prev Med. 2011 Jan;2(1):4-9.
- Trehan A, Winterbottom J, Lane B, et al; End-stage renal disease in Indo-Asians in the North-West of England. QJM. 2003 Jul;96(7):499-504.
- Pyelonephritis, Chronic, Medical Disability Advisor, 2010
- Mohammadjafari H, Aalaee A, Salehifar E, et al; Doppler ultrasonography as a predictive tool for permanent kidney damage Iran J Kidney Dis. 2011 Nov;5(6):386-91.
- Senija R, Jasminka D, Kenana A, et al; Our experiences in kidney transplantation and monitoring of kidney graft Bosn J Basic Med Sci. 2005 May;5(2):43-8.
- McCullough PA, Steigerwalt S, Tolia K, et al; Cardiovascular disease in chronic kidney disease: data from the Kidney Early Curr Diab Rep. 2011 Feb;11(1):47-55.
- Ardissino G, Avolio L, Dacco V, et al; Long-term outcome of vesicoureteral reflux associated chronic renal failure in J Urol. 2004 Jul;172(1):305-10.
- Guidelines on Paediatric Urology, European Association of Urology (2011)
- Stapleton AE, Dziura J, Hooton TM, et al; Recurrent urinary tract infection and urinary Escherichia coli in women ingesting Mayo Clin Proc. 2012 Feb;87(2):143-50.
- Nickel JC; Practical management of recurrent urinary tract infections in premenopausal Rev Urol. 2005 Winter;7(1):11-7.
- Smaill F, Vazquez JC; Antibiotics for asymptomatic bacteriuria in pregnancy. Cochrane Database Syst Rev. 2007 Apr 18;(2):CD000490.
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Dr Laurence Knott
Dr Laurence Knott
Dr Adrian Bonsall