However, a bacterial finding alone does not mean an infection requiring treatment. It can also be asymptomatic bacteriuria or sample contamination, meaning bacteria introduced during collection. Sampling method, test results and the cat's clinical situation affect treatment decisions.
When to see a vet urgently
Go to an emergency vet immediately if your cat has any of the following:
- repeated attempts to urinate with no urine or only a few drops
- painful straining together with vomiting or marked lethargy
- collapse or clearly reduced responsiveness
- urinary signs with a severe deterioration in general condition and failure to eat
Urethral blockage is life-threatening, particularly in males. Do not wait for a urine culture result if no urine is passed. You can find a vet near you.
Overview
A healthy cat's urine is normally sterile. Bacteria entering the urinary tract cause inflammation, which may appear as mild discomfort or lead to severe cystitis or pyelonephritis. Sometimes bacteriuria remains entirely symptom-free and is detected only in a urine sample, making regular investigations particularly important in at-risk animals.
Bacteria do not always trigger symptomatic inflammation, however. Cystitis means bladder inflammation, whereas pyelonephritis is a kidney infection. In asymptomatic bacteriuria, bacteria grow from the sample but no clinical signs consistent with urinary tract infection are found.
Painful urination in a young, otherwise healthy cat often has a cause other than bacteria. Idiopathic cystitis and urinary stones, for example, can produce the same signs. A “urinary infection” reported by an owner is therefore initially a description of suspected symptoms rather than a confirmed bacterial diagnosis. Infection likelihood is assessed alongside age and other diseases.
Causes
The most common causes of bacteriuria in cats include:
- bacterial bladder infection, or cystitis
- pyelonephritis, or kidney infection
- urinary stones and crystals that damage mucous membranes
- bladder catheterisation
- weakened immune defences
- anatomical factors, with females having a shorter, wider urethra
Bacteria can ascend through the urethra into the bladder. They often come from the cat's own intestinal or genital-area microbiota rather than infection acquired from another cat. Identifying a bacterial species alone does not establish which part of the urinary tract contains any infection.
Stones or crystals do not produce bacteria themselves. Common feline struvite and calcium oxalate stones can occur without infection. Conversely, a urinary stone or another structural problem can maintain recurrent infections. Crystal and bacterial findings are therefore assessed separately, although they may coexist.
Risk factors
- Older age.
- Chronic kidney disease.
- Female cats, particularly unspayed females.
- Animals that have undergone urinary tract surgery.
- Overweight and inactive cats.
Female sex and older age are repeatedly described risk factors, but similarly firm evidence for the particular importance of being unspayed is lacking. Information linking every listed factor specifically to bacteriuria in cats is limited; obesity, for example, is also associated with other urinary diseases.
Chronic kidney disease, diabetes and hyperthyroidism can be associated with bacterial findings. Their presence alone is not, however, an indication for antibiotics. Catheterisation also does not mean a symptom-free cat automatically receives a preventive antibiotic.
Symptoms
Bacteriuria can occur in two ways:
- Asymptomatic: a hidden form found only through testing.
- Symptomatic, with signs of urinary tract infection:
- Frequent, painful urination.
- Blood in the urine, called haematuria.
- Foul-smelling urine.
- Urine leakage or urinating outside the tray.
- Reduced appetite and activity.
Urine smell or blood does not confirm bacterial disease. Frequent urination and urinating outside the tray can also be associated with non-infectious bladder pain. Signs are not interpreted as merely behavioural before a medical cause is assessed.
Establishing a lack of symptoms requires careful observation. An outdoor cat's urination is not always seen, and in a multi-cat home it may be unclear which cat visits the tray frequently. Tell your vet when an observation is uncertain. Describing straining, urine volume and behaviour is more useful than simply assuming infection.
Complications
Untreated bacteriuria can lead to serious consequences:
- chronic cystitis
- pyelonephritis
- kidney damage
- sepsis if bacteria spread into the blood
- reduced quality of life
Serious consequences relate to clinical infection, such as infection reaching the kidneys; they are not an inevitable progression of asymptomatic bacteriuria. A symptom-free finding alone is therefore not usually treated with an antibiotic to prevent them. Bacteriuria may also resolve on its own or persist without illness.
In a study following older cats, asymptomatic bacterial findings were not treated with antibiotics and were not associated with shorter survival. The study involved a selected group, so it does not exclude serious infection in an individual with symptoms. It does, however, support the distinction between a laboratory finding and disease requiring treatment.
A cat with pyelonephritis may be apathetic, not eating or vomiting. Fever and abdominal pain are not present in every patient. Infection can cause acute kidney injury even in a cat with pre-existing kidney disease. This requires assessment of the whole patient and often blood tests, rather than merely monitoring bladder signs.
Diagnosis at the vet
The following are used to confirm diagnosis:
- routine urine analysis to identify bacteria and inflammatory findings
- urine culture to identify the bacterial species
- blood tests to assess kidney function
- bladder and kidney ultrasound
- X-rays where necessary to rule out urinary stones
A reliable sample and culture
Free-catch urine can acquire bacteria from the skin or collection container. During cystocentesis, your vet takes a sample directly from the bladder with a needle, reducing contamination. Even this method does not, on its own, distinguish asymptomatic bacteriuria from clinical infection: symptoms and other investigations must be assessed.
Routine urine analysis examines concentration, blood and microscopic sediment, for example. Small debris can resemble bacteria, and the white blood cell field on a dipstick is not a reliable infection test in cats. Culture grows microbes in the laboratory; bacterial numbers are interpreted in relation to sample collection method.
Susceptibility testing, or an antibiogram, helps select a medicine if treatment is needed. Handling and transport affect reliability, so agree on home collection in advance. Report antibiotics used too. The aim is to examine or store the sample according to laboratory instructions as soon as possible.
What does imaging show?
Ultrasound and X-rays do not identify bacterial species but look for urinary stones and structural changes, for example. Kidney values reflect kidney function rather than identifying the site of bacterial infection on their own. If kidney infection is suspected, results are compared with systemic signs and other possible causes of kidney injury.
According to ISCAID (2019), asymptomatic bacteriuria, bacteria in urine without signs of illness, is not usually treated with antibiotics in cats. Treatment is needed for bladder infection symptoms, such as frequent, painful urination and blood in urine, before urinary surgery or at your vet's discretion. Unnecessary antibiotic courses increase bacterial resistance.
Urinary signs alone are therefore not an antibiotic indication without assessment of bacterial involvement. Conversely, care of a seriously ill cat is not delayed solely because of principles for asymptomatic bacteriuria. Current guidance supports this distinction, and your vet assesses possible exceptions.
Treatment and follow-up
When symptomatic bacterial infection is confirmed, treatment is selected from culture, susceptibility results and infection location. Bladder pain can be treated with medication prescribed by your vet. With pyelonephritis, the team considers that infection lies within kidney tissue rather than urine alone, and assesses other supportive care needs.
Asymptomatic bacteriuria is treated only in a justified exceptional situation. This may include a planned urinary procedure or suspicion that the finding contributes to poor diabetes control. Identifying a bacterium resistant to many antibiotics does not itself make a symptom-free finding require treatment or become more dangerous than usual.
If symptoms fail to improve or return, reassessment is needed. Repeated identification of the same bacterium may suggest recurrence from a remaining infection site; a different bacterium can mean a new infection. Your vet compares previous cultures and looks for a stone or a problem affecting bladder emptying, for example.
Monitoring is agreed according to symptoms and the underlying disease. A symptom-free cat's positive result is not automatically targeted with repeated antibiotic courses to make it negative. Do not start leftover medicine for a new urinary symptom because a different disease or urinary blockage may be responsible.
Prevention
Bacteriuria can be prevented through:
- regular urine tests for older cats
- keeping the litter tray clean
- access to clean water and good-quality food
- prevention and treatment of cystitis and urinary stones
- monitoring weight and exercise
These measures support urinary health but have not been shown to reliably prevent every bacterial finding. The need and timing of urine tests are selected individually. There is little research on cranberry products, probiotics and other supplements for treating or preventing recurrent feline infections.
Keep water easily accessible and discuss a diet with more moisture if suitable for your cat's other conditions. Provide a sufficiently large, clean litter tray in a quiet place. A low entrance helps an older or stiff cat use it. Access must not require climbing over furniture or passing another animal in a cramped area.
Several well-positioned trays help in a multi-cat home. Remove waste regularly and avoid heavily scented litter if your cat dislikes it. Do not punish changes in tray use; investigate pain, access barriers and other causes.
This text provides general information and does not replace veterinary care. Contact a vet if your cat develops symptoms.
Frequently asked questions
Does urine containing bacteria always need an antibiotic?
No. Asymptomatic bacteriuria is usually not treated with antibiotics. The decision relies on a reliable sample, symptoms and other health conditions, rather than a positive culture alone.
Can bacteria come from sample collection?
Yes. A free-catch sample can be contaminated with bacteria from skin, the container or environment. Your vet assesses the collection method and whether a confirmatory sample directly from the bladder is needed.
Can a cat have kidney infection without fever?
Yes. Fever is not an essential finding in pyelonephritis. Vomiting, failure to eat or marked apathy with urinary findings require closer assessment, particularly in a cat with pre-existing kidney disease.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
- Bacterial Cystitis in Small Animals, Merck Veterinary Manual, accessed 2026-11-03.
- Feline Lower Urinary Tract Disease, Cornell University, accessed 2026-11-03.
- Diagnostic testing, American Animal Hospital Association, accessed 2026-11-03.
- Subclinical Bacteriuria in Older Cats and its Association with Survival, Journal of Veterinary Internal Medicine / PubMed, accessed 2026-11-03.
- Pyelonephritis in Small Animals, Merck Veterinary Manual, accessed 2026-11-03.
- 2025 iCatCare consensus guidelines on the diagnosis and management of lower urinary tract diseases in cats, International Cat Care / Journal of Feline Medicine and Surgery, accessed 2026-11-03.
- Litter Boxes, The Ohio State University, accessed 2026-11-03.
- Urinary Tract Infections in Cats, VCA, accessed 2026-11-03.