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Infectious Disease and Microbiology – Pyelonephritis
Pyelonephritis is a common infection of the upper urinary tract that causes inflammation of the renal pelvis, calyces, and renal parenchyma. It may present as acute uncomplicated pyelonephritis, acute complicated pyelonephritis, chronic pyelonephritis, or xanthogranulomatous pyelonephritis. Chronic pyelonephritis is characterized by uneven renal scarring and chronic inflammatory changes involving the renal interstitium and tubules.
The disease is much more common in females than males. Young women, infants, and elderly individuals are the most commonly affected groups. In the United States, more than 250,000 cases occur annually.
Risk factors include pregnancy, urinary obstruction due to prostate disease or urethral narrowing, renal stones, diabetes mellitus, and recurrent lower urinary tract infections. In young women, frequent sexual intercourse, spermicide use, stress incontinence, a new sexual partner, and a personal or maternal history of urinary tract infection significantly increase risk. Prevention focuses on early diagnosis and treatment of lower urinary tract infections and reduction of modifiable risk factors such as spermicide use.
Most infections occur by ascending spread of pathogens from the urethra to the bladder and then through the ureters to the kidneys. Less commonly, hematogenous spread occurs, especially with gram-positive organisms or fungal infections.
The most common causative organism is Escherichia coli, responsible for approximately 80% of cases. Other pathogens include Proteus species and Klebsiella species. Less common causes include Pseudomonas aeruginosa, enterococci, and Staphylococcus saprophyticus. Isolation of Staphylococcus aureus from urine often suggests bacteremia. Emphysematous pyelonephritis, a severe gas-forming necrotizing infection, is commonly caused by E. coli and Klebsiella species and occasionally by Candida species.
Symptoms may develop over several hours or days. Patients commonly experience fever, chills, nausea, vomiting, malaise, headache, flank pain, back pain, abdominal pain, and symptoms of lower urinary tract infection such as dysuria, urgency, and hematuria. Elderly patients may present with few symptoms, while children often present nonspecifically.
Physical examination commonly reveals fever, tachycardia, flank tenderness, and sometimes signs of sepsis or dehydration. Toxic appearance may indicate severe infection.
Diagnosis begins with urinalysis demonstrating pyuria and bacteriuria, although absence of bacteria does not exclude pyelonephritis. Pretreatment urine cultures are essential. Laboratory studies may show leukocytosis with left shift, elevated ESR and CRP, and abnormal renal function tests. Blood cultures may be helpful in severe cases.
Imaging is reserved for atypical presentations, recurrent disease, suspected obstruction, or failure to improve within 72 hours of therapy. Plain abdominal radiographs may identify calculi or gas formation in emphysematous pyelonephritis. Ultrasonography is preferred initially for recurrent or atypical disease. Contrast-enhanced CT scanning provides better evaluation of obstruction, abscesses, or complicated anatomy. Repeat ultrasonography may be necessary if deterioration occurs despite treatment.
The differential diagnosis includes cystitis, urethritis, vaginitis, appendicitis, pelvic inflammatory disease, and tumors of the kidney or bladder.
Treatment depends on disease severity and whether the infection is complicated. Outpatient therapy for uncomplicated acute pyelonephritis may include oral amoxicillin, amoxicillin-clavulanate, trimethoprim-sulfamethoxazole, ciprofloxacin, levofloxacin, norfloxacin, or cefpodoxime. Fluoroquinolones are commonly used because of their excellent renal tissue penetration. Treatment generally lasts 10–14 days, although high-dose levofloxacin may be given for 5 days.
Hospitalized patients require intravenous therapy with agents such as ciprofloxacin, levofloxacin, ceftriaxone, gentamicin, ampicillin, aztreonam, imipenem-cilastatin, ertapenem, or ticarcillin-clavulanic acid. Once fever resolves and clinical improvement occurs, patients are transitioned to oral therapy to complete the course.
Supportive care includes rest, analgesics, antiemetics, and adequate hydration. Intravenous fluids are especially important in septic or dehydrated patients.
Consultation with a urologist is indicated when urinary obstruction or structural abnormalities are present, as surgical correction may be necessary. Infectious disease consultation is helpful for unusual or resistant organisms such as Pseudomonas aeruginosa or extended-spectrum beta-lactamase–producing bacteria.
Surgical intervention may be necessary in emphysematous pyelonephritis, renal or perinephric abscess, renal calculi, or xanthogranulomatous pyelonephritis.
Hospital admission is recommended for severe illness, high fever, significant pain, dehydration, inability to tolerate oral medications, poor compliance, or pregnancy. Patients may be discharged after 24–48 hours of clinical improvement and defervescence.
Follow-up includes post-treatment urine cultures and further imaging or laboratory testing in patients with persistent symptoms. Patients should be advised to complete prescribed antibiotic courses and maintain adequate fluid intake.
Acute uncomplicated pyelonephritis generally carries an excellent prognosis, with overall in-hospital mortality below 1–2%. Complications include bacteremia, septic shock, renal abscess, perinephric abscess, and formation of struvite stones, particularly with Proteus infections.
Pyelonephritis is a common infection of the upper urinary tract that causes inflammation of the renal pelvis, calyces, and renal parenchyma. It may present as acute uncomplicated pyelonephritis, acute complicated pyelonephritis, chronic pyelonephritis, or xanthogranulomatous pyelonephritis. Chronic pyelonephritis is characterized by uneven renal scarring and chronic inflammatory changes involving the renal interstitium and tubules.
The disease is much more common in females than males. Young women, infants, and elderly individuals are the most commonly affected groups. In the United States, more than 250,000 cases occur annually.
Risk factors include pregnancy, urinary obstruction due to prostate disease or urethral narrowing, renal stones, diabetes mellitus, and recurrent lower urinary tract infections. In young women, frequent sexual intercourse, spermicide use, stress incontinence, a new sexual partner, and a personal or maternal history of urinary tract infection significantly increase risk. Prevention focuses on early diagnosis and treatment of lower urinary tract infections and reduction of modifiable risk factors such as spermicide use.
Most infections occur by ascending spread of pathogens from the urethra to the bladder and then through the ureters to the kidneys. Less commonly, hematogenous spread occurs, especially with gram-positive organisms or fungal infections.
The most common causative organism is Escherichia coli, responsible for approximately 80% of cases. Other pathogens include Proteus species and Klebsiella species. Less common causes include Pseudomonas aeruginosa, enterococci, and Staphylococcus saprophyticus. Isolation of Staphylococcus aureus from urine often suggests bacteremia. Emphysematous pyelonephritis, a severe gas-forming necrotizing infection, is commonly caused by E. coli and Klebsiella species and occasionally by Candida species.
Symptoms may develop over several hours or days. Patients commonly experience fever, chills, nausea, vomiting, malaise, headache, flank pain, back pain, abdominal pain, and symptoms of lower urinary tract infection such as dysuria, urgency, and hematuria. Elderly patients may present with few symptoms, while children often present nonspecifically.
Physical examination commonly reveals fever, tachycardia, flank tenderness, and sometimes signs of sepsis or dehydration. Toxic appearance may indicate severe infection.
Diagnosis begins with urinalysis demonstrating pyuria and bacteriuria, although absence of bacteria does not exclude pyelonephritis. Pretreatment urine cultures are essential. Laboratory studies may show leukocytosis with left shift, elevated ESR and CRP, and abnormal renal function tests. Blood cultures may be helpful in severe cases.
Imaging is reserved for atypical presentations, recurrent disease, suspected obstruction, or failure to improve within 72 hours of therapy. Plain abdominal radiographs may identify calculi or gas formation in emphysematous pyelonephritis. Ultrasonography is preferred initially for recurrent or atypical disease. Contrast-enhanced CT scanning provides better evaluation of obstruction, abscesses, or complicated anatomy. Repeat ultrasonography may be necessary if deterioration occurs despite treatment.
The differential diagnosis includes cystitis, urethritis, vaginitis, appendicitis, pelvic inflammatory disease, and tumors of the kidney or bladder.
Treatment depends on disease severity and whether the infection is complicated. Outpatient therapy for uncomplicated acute pyelonephritis may include oral amoxicillin, amoxicillin-clavulanate, trimethoprim-sulfamethoxazole, ciprofloxacin, levofloxacin, norfloxacin, or cefpodoxime. Fluoroquinolones are commonly used because of their excellent renal tissue penetration. Treatment generally lasts 10–14 days, although high-dose levofloxacin may be given for 5 days.
Hospitalized patients require intravenous therapy with agents such as ciprofloxacin, levofloxacin, ceftriaxone, gentamicin, ampicillin, aztreonam, imipenem-cilastatin, ertapenem, or ticarcillin-clavulanic acid. Once fever resolves and clinical improvement occurs, patients are transitioned to oral therapy to complete the course.
Supportive care includes rest, analgesics, antiemetics, and adequate hydration. Intravenous fluids are especially important in septic or dehydrated patients.
Consultation with a urologist is indicated when urinary obstruction or structural abnormalities are present, as surgical correction may be necessary. Infectious disease consultation is helpful for unusual or resistant organisms such as Pseudomonas aeruginosa or extended-spectrum beta-lactamase–producing bacteria.
Surgical intervention may be necessary in emphysematous pyelonephritis, renal or perinephric abscess, renal calculi, or xanthogranulomatous pyelonephritis.
Hospital admission is recommended for severe illness, high fever, significant pain, dehydration, inability to tolerate oral medications, poor compliance, or pregnancy. Patients may be discharged after 24–48 hours of clinical improvement and defervescence.
Follow-up includes post-treatment urine cultures and further imaging or laboratory testing in patients with persistent symptoms. Patients should be advised to complete prescribed antibiotic courses and maintain adequate fluid intake.
Acute uncomplicated pyelonephritis generally carries an excellent prognosis, with overall in-hospital mortality below 1–2%. Complications include bacteremia, septic shock, renal abscess, perinephric abscess, and formation of struvite stones, particularly with Proteus infections.
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