MRSA UTI: MRSA in the urinary tract

MRSA can cause a urinary tract infection, but it accounts for only a small share of UTIs. Escherichia coli and other gut bacteria dominate. When MRSA appears in urine, the near-universal context is a urinary catheter, recent urological surgery, a care home or hospital stay, or known MRSA carriage. A positive result without symptoms is usually left untreated.

A MRSA UTI does not feel different from any other UTI. The typical features are:

• Burning, stinging or pain when passing urine.
• Going more often, and a sudden urgent need to go.
• Cloudy, dark or strong-smelling urine.
• Aching or pressure low in the abdomen.
• Blood in the urine.

Seek urgent medical help for fever and shivering, pain in the back or side below the ribs, vomiting, new confusion or drowsiness — particularly in an older person or someone with a catheter. Those point to kidney involvement or MRSA in the bloodstream.

• Urinary catheters — the main route. The tube bypasses the body's defences and gives bacteria a surface on which to build a biofilm that antibiotics penetrate poorly. Risk rises with every additional day the catheter stays in.
• Urological procedures — cystoscopy, stents, prostate surgery and other instrumentation.
• Seeding from the bloodstream — MRSA circulating in the blood can lodge in the kidney, which is why a urine result sometimes signals a deeper problem.
• Existing carriage — MRSA already colonising the skin, groin or perineum is well placed to reach the urethra.

Bacteria in the urine of someone with no urinary symptoms is called asymptomatic bacteriuria. It is extremely common in people with long-term catheters, and major guidance advises against treating it with antibiotics: treatment does not improve outcomes and accelerates resistance. The recognised exceptions are pregnancy and the run-up to an invasive urological procedure. Treatment is reserved for people who actually have symptoms.

Because Staphylococcus aureus in urine is associated with bloodstream infection more often than typical urinary organisms are, clinicians frequently take blood cultures and hunt for another source at the same time.

Diagnosis rests on a urine culture, ideally taken before antibiotics start. The laboratory identifies the organism and runs susceptibility testing, which is what determines the choice of drug. If a catheter has been in place a while, a fresh sample is usually taken after changing or removing it, since the old tube's biofilm is not representative of the bladder.

Two things matter more than the antibiotic itself: removing or replacing the catheter where possible, and matching the drug to the culture result. Broadly:

• Lower urinary tract, MRSA susceptible — trimethoprim-sulfamethoxazole, nitrofurantoin or doxycycline, typically for a short course.
• Kidney involvement or systemic illness — intravenous therapy such as vancomycin, daptomycin or linezolid. Nitrofurantoin is unsuitable here because it does not reach useful levels in kidney tissue.
• Catheter management — remove it if it is no longer needed, or exchange it, since the biofilm shelters bacteria from any antibiotic.

The full drug list, with routes and roles, is on MRSA antibiotics.

Nearly all prevention is catheter prevention: avoid catheters that are not needed, remove them as early as possible, insert them aseptically, keep the drainage bag below bladder level and the system closed, and wash hands before and after any contact with the tubing. Household precautions for anyone with MRSA are covered on MRSA at home.