Lucan · Conditions

Lower urinary tract infection

Australian guidance: eTG Antibiotic — Urinary Tract Infections

1. Definition and epidemiology

Lower urinary tract infection (UTI) refers to infection confined to the bladder (acute cystitis) and urethra, without involvement of the upper urinary tract. It is one of the most common bacterial infections in adults, with women bearing a disproportionate burden due to anatomical factors including a shorter urethra and proximity of the urethral meatus to the rectum. In Australia, lower UTI accounts for a substantial proportion of antibiotic prescriptions in primary care, making appropriate antibiotic stewardship a priority.

2. Pathophysiology

Most lower UTIs are caused by ascending colonisation of the bladder via periurethral flora. Escherichia coli accounts for 70 to 95% of uncomplicated UTIs in adults without anatomical or functional abnormalities of the urinary tract. E. coli virulence factors including type 1 and P fimbriae facilitate adhesion to uroepithelial cells, while alpha haemolysin damages the epithelial barrier and iron acquisition systems (siderophores) allow bacterial survival in the nutrient-poor urine environment. Other pathogens include Klebsiella pneumoniae, Proteus mirabilis, and Staphylococcus saprophyticus, the last being a recognised cause of acute cystitis in young sexually active women. The host inflammatory response to bladder wall invasion generates the classical symptoms of dysuria, frequency, and urgency without systemic features. In anatomically or functionally abnormal urinary tracts, a broader spectrum of organisms including Pseudomonas aeruginosa can establish infection and cause more invasive disease (Robbins Ch 20).

3. Clinical presentation and diagnostic criteria

The clinical diagnosis of uncomplicated lower UTI in non-pregnant adult women rests on the combination of at least two of the following: dysuria, urinary frequency, urgency, and suprapubic discomfort, in the absence of vaginal discharge or irritation. Examination findings are limited and may include mild suprapubic tenderness on palpation. There should be no fever, costovertebral angle tenderness, or haematogenous features, as these suggest upper tract involvement (pyelonephritis). In older adults, lower UTI may present atypically with functional decline, confusion, or falls, though asymptomatic bacteriuria in this population does not require treatment. In men, a lower UTI should prompt consideration of prostatitis or structural abnormality given the relative rarity of simple cystitis in this group.

4. Investigations and AU-specific cutoffs

In typical uncomplicated lower UTI in non-pregnant premenopausal women, urine dipstick testing is a reasonable first step. Positive leucocyte esterase and nitrites together confer high specificity for bacterial infection. Midstream urine (MSU) for microscopy, culture, and sensitivity (MCS) is not mandatory in straightforward uncomplicated cystitis presenting with classical symptoms, but is indicated in men, pregnant women, patients with recurrent UTI, those with recent antibiotic exposure, and residents of aged care facilities. The standard AU microbiological threshold for significant bacteriuria on MSU is greater than or equal to 10 to the power of 8 colony-forming units per litre (10^5 CFU/mL) of a single uropathogen, though lower thresholds may be clinically relevant in symptomatic women. Renal tract imaging is not indicated for a first episode of uncomplicated lower UTI in adults.

5. Management

Management is guided by eTG Antibiotic. Empirical antibiotic choice for acute uncomplicated cystitis in non-pregnant adults is informed by local E. coli resistance patterns and consideration of antibiotic stewardship principles. First-line options for uncomplicated acute cystitis include nitrofurantoin monohydrate/macrocrystals 100 mg orally twice daily for five days (preferred in women without renal impairment), trimethoprim 300 mg orally once daily at night for three days, or cefalexin 500 mg orally twice daily for five to seven days. Trimethoprim should be used with caution when there has been antibiotic exposure in the preceding one to six months, as this is a recognised risk factor for trimethoprim-resistant E. coli. Fosfomycin trometamol 3 g orally as a single dose is an alternative with activity against most extended-spectrum beta-lactamase (ESBL)-producing E. coli strains. Pivmecillinam, although effective for cystitis, is not registered in Australia and requires access via the Special Access Scheme. Non-pregnant women with an uncomplicated episode do not require a test-of-cure urine culture unless symptoms persist or recur. In men, a minimum of seven days of antibiotic therapy is recommended to account for potential occult prostatitis.

6. Pharmacology and AU PBS notes

Nitrofurantoin (AU brands: Macrobid, Macrodantin) acts by generating reactive oxygen species that damage bacterial DNA, RNA, and protein synthesis. It is active against E. coli, Staphylococcus saprophyticus, and most Enterococcus species, but lacks activity against Proteus, Klebsiella, or Pseudomonas. It should be avoided when estimated glomerular filtration rate (eGFR) is less than 30 mL/min per 1.73 m^2 due to inadequate urinary drug levels and risk of peripheral neuropathy. On the Pharmaceutical Benefits Scheme (PBS), nitrofurantoin 100 mg capsules are listed under streamlined authority (Restriction Code 5214) for uncomplicated lower UTI in women. Trimethoprim 300 mg tablets are PBS-listed and are a low-cost alternative, though rates of E. coli resistance are rising in Australia. Cefalexin (AU brand: Keflex) is a first-generation cephalosporin with good urinary penetration and is PBS general benefit. Fosfomycin trometamol (AU brand: Fosfocin) 3 g granules for oral solution are not currently PBS-subsidised for UTI in Australia and attract full cost. Ciprofloxacin should be reserved for complicated UTI or culture-directed therapy given the need to preserve fluoroquinolone activity.

7. Complications and monitoring

Untreated or undertreated lower UTI can ascend to cause pyelonephritis, which carries a risk of bacteraemia and sepsis, particularly in vulnerable populations including pregnant women, diabetic patients, and immunocompromised individuals. Recurrent UTI (defined as two or more episodes in six months or three or more in twelve months) warrants investigation for risk factors including incomplete bladder emptying, genitourinary prolapse, or structural abnormality. Low-dose prophylactic nitrofurantoin or trimethoprim (at night) is an option for women with frequent recurrence, as is post-coital prophylaxis where intercourse is a clear trigger. Nitrofurantoin used for prolonged periods carries a rare risk of pulmonary toxicity (acute or chronic hypersensitivity pneumonitis) and hepatotoxicity; patients on long-term therapy require periodic monitoring of renal function and liver enzymes. Pregnant women with any bacteriuria, whether symptomatic or asymptomatic, require prompt treatment and test-of-cure culture due to the risk of preterm labour and pyelonephritis. The emergence of multidrug-resistant E. coli, including ESBL-producing strains, is a growing concern in Australia; rates of ESBL-producing E. coli in bloodstream infections vary from 6% in Tasmania to 25% in the Northern Territory based on 2023 AURA data, reinforcing the importance of culture-directed therapy when empirical treatment fails.

Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.