Urinary Tract & Intra-abdominal Infections

Cystitis and pyelonephritis

Dysuria without fever is bladder-only. Acute cystitis causes dysuria, frequency, urgency, and suprapubic pain WITHOUT fever or flank pain. Escherichia coli causes ~80%; Staphylococcus saprophyticus affects young, sexually active women; Proteus makes urease and struvite stones. Urinalysis shows pyuria with positive leukocyte esterase and nitrites, which signal gram-negative rods that convert nitrate to nitrite. A healthy nonpregnant woman with typical symptoms can be treated without a culture; culture pyelonephritis, complicated or recurrent UTI, men, and pregnancy.

Fever and flank pain move it upstairs. Acute pyelonephritis adds fever, chills, flank or costovertebral-angle tenderness, and nausea or vomiting, with or without cystitis symptoms. White blood cell casts are specific for a renal (upper tract) source. E. coli is again the leading pathogen.

Spare the fluoroquinolones. Reserve them for pyelonephritis or for when first-line agents cannot be used, given collateral resistance and tendon and QT toxicity. Nitrofurantoin and fosfomycin concentrate in the bladder but not the kidney, so they are not used for pyelonephritis.

Not better in 72 hours? Get a CT. If pyelonephritis has not improved within 48–72 hours of appropriate therapy, image with CT to find a perinephric abscess or obstructing stone needing drainage.

Complicated, catheter-associated, and recurrent UTI

Host factors define complicated disease. A UTI is complicated when host or structural factors raise the risk of failure: male sex, pregnancy, an indwelling catheter, obstruction or stones, immunosuppression, renal transplant, or a urologic abnormality. Complicated UTIs need longer courses, often broader coverage, and a culture; image if the patient is septic, obstruction is suspected, or there is no improvement in 48 to 72 hours.

CAUTI: symptoms first, then pull the catheter. Catheter-associated UTI is diagnosed only with genuine symptoms plus bacteriuria; pyuria alone is not enough, because long-term catheters are almost always colonized. Management includes removing or replacing the catheter. Do not culture or treat asymptomatic catheterized patients.

Recurrent UTI is 2 or more infections in 6 months or 3 or more in a year. Options are behavioral measures, postcoital or continuous low-dose prophylaxis (TMP-SMX or nitrofurantoin), and topical vaginal estrogen in postmenopausal women, which restores the protective vaginal flora.

Postmenopausal recurrent UTIs respond well to topical (vaginal) estrogen.

Asymptomatic bacteriuria and pregnancy

Treat only pregnancy and pre-procedure. Asymptomatic bacteriuria (a positive culture without symptoms) is treated ONLY in pregnant women and before urologic procedures with anticipated mucosal bleeding. Do NOT treat the elderly, diabetics, or catheterized patients otherwise; treatment breeds resistance and C. difficile without benefit. Cloudy or foul-smelling urine by itself is not a symptom.

Screen every pregnancy. Screen all pregnant women for bacteriuria at the first prenatal visit and treat it, which reduces pyelonephritis, preterm birth, and low birth weight; a follow-up culture confirms clearance. Pyelonephritis in pregnancy usually calls for admission and IV antibiotics; ACOG allows outpatient oral therapy for selected mild cases before about 24 weeks with close follow-up.

Intra-abdominal infection

Perforation spills a polymicrobial soup. Secondary bacterial peritonitis and intra-abdominal abscess follow perforation or inflammation (appendicitis, diverticulitis, perforated viscus). The flora are polymicrobial gut organisms: gram-negative rods (E. coli), anaerobes (Bacteroides fragilis), and enterococci. CT localizes the source.

Source control beats any antibiotic. Intra-abdominal infection needs source control (percutaneous drainage or surgery) PLUS empiric coverage of gram-negative rods and anaerobes: ceftriaxone + metronidazole, piperacillin-tazobactam, or ertapenem for community-acquired disease. Broaden for healthcare-associated infection, adding antipseudomonal and enterococcal coverage. Once the source is controlled, a short course of about 4 days is usually enough.

Antibiotics cannot cure an undrained abscess; drainage or surgical source control is essential.

Spontaneous bacterial peritonitis

Cirrhosis plus 250 PMNs equals SBP. SBP is infection of cirrhotic ascites without a surgical source, diagnosed by an ascitic PMN count ≥250 cells/mm³. It is monomicrobial (E. coli, Klebsiella, S. pneumoniae). Signs can be subtle (fever, abdominal tenderness, worsening encephalopathy or kidney function), so tap any cirrhotic admitted with ascites. Treat with IV cefotaxime or ceftriaxone plus albumin, which prevents hepatorenal syndrome, and continue secondary prophylaxis with daily ciprofloxacin or TMP-SMX (norfloxacin is not available in the US).