Uncomplicated urinary tract infections occur when common bacteria infect the lower urinary tract of otherwise healthy females. Any urinary tract infection that does not fit this description is a complicated one.

The vast majority of urinary tract infections (UTIs) are uncomplicated. People can treat them with antibiotics, and they should resolve without issue. Complicated cases can last longer, cause additional symptoms, and be harder to treat.

In this article, we examine the differences between uncomplicated and complicated UTIs. This includes their symptoms, causes, treatment options, and outlook.

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Doctors class a UTI as uncomplicated if it occurs in the urethra or bladder and the person it affects:

  • is female
  • is not pregnant
  • does not have a weakened immune system
  • does not have a fever
  • is otherwise healthy

The urethra and bladder are also known as the lower urinary tract. Some may refer to UTIs affecting the bladder as bladder infections or cystitis. Bladder infections are the most common form of UTI.

Uncomplicated UTIs also only occur due to specific bacteria, which are behind the vast majority of cases. If a different bacteria causes the UTI, doctors will consider it to be a complicated UTI.

A complicated UTI is any urinary tract infection that does not fit the criteria of an uncomplicated UTI. If a doctor thinks that the UTI will be difficult to treat or could lead to complications, they will define it as a complicated UTI.

Complicated UTIs can affect:

  • the kidneys and ureters
  • males
  • pregnant people
  • people with weakened immune systems
  • people who have recently had surgery in the area
  • people with indwelling catheters

A UTI can also be a complicated case if the bacteria that cause it are ones that do not typically cause UTIs. In the United States, there are over 626,000 hospital admissions each year for complicated UTIs.

Complicated and uncomplicated UTIs share many symptoms.

Potential symptoms can include:

In children

The symptoms of UTI can be vague in children below age 2 years. They can include:

  • fever
  • irritability
  • problems with feeding
  • vomiting
  • recurrent tummy pain
  • changes to urination habits

After age 2 years, UTI symptoms tend to be similar to those experienced by adults.

Most UTIs occur due to bacterial infection. In many cases, these bacteria can travel to the urinary tract from the skin in and around the rectum and genitals.

Bacteria can pass into the urinary tract in many ways, such as through sexual intercourse or the insertion of a catheter.

Uncomplicated UTIs

Bacteria strains that could cause uncomplicated UTIs include:

  • E. coli
  • Klebsiella
  • Proteus
  • Enterobacter
  • Enterococcus

E. coli and Klebsiella cause the vast majority of uncomplicated UTIs.

Complicated UTIs

The same bacteria that cause uncomplicated UTIs can also cause complicated UTIs.

A range of different microbes can also cause complicated UTIs. This includes different bacteria and, in some cases, fungi such as Candida. Some bacteria that cause complicated UTIs may be resistant to antibiotic treatment.

When diagnosing a urinary tract infection, doctors will discuss a person’s symptoms and medical history before carrying out tests.

Uncomplicated UTIs

Doctors will collect a urine sample from the individual. How it looks and smells may suggest that an infection is present.

They will also analyze the sample to check its acidity and see if any bacteria or white blood cells are present. Additionally, they will perform a urine culture to check for bacteria.

Complicated UTIs

To diagnose complicated UTIs, doctors will carry out the tests mentioned above but may also use a number of others to gain more information.

Doctors may request a urine culture test, which is where they send a urine sample to a lab to check for specific germs. They can also help guide further treatment if someone is not seeing any improvement with antibiotics.

People may need to have an ultrasound or CT scan to check for any problems with the kidneys or ureters, such as the presence of kidney stones.

Some doctors may also request a cystoscopy, which is a procedure allowing doctors to look at the bladder using a tool called a cystoscope.

Doctors will typically treat UTIs with antibiotics.

Uncomplicated UTIs

Uncomplicated UTIs should resolve with a course of antibiotics.

If a person’s symptoms are causing a lot of discomfort, they may also need to take medication to reduce the pain.

Complicated UTIs

The treatment for a complicated UTI will depend on the factors that have made it complicated. In some cases, people will need to receive treatment in the hospital.

Doctors may start with a course of broad-spectrum antibiotics, which target a variety of different bacteria. Once doctors know which bacteria have caused the infection, they can switch to a more specific antibiotic.

Different medications may be necessary to treat the following:

Doctors may also remove kidney stones or indwelling catheters if they are involved in the infection.

Uncomplicated UTIs tend to resolve more quickly and simply than complicated cases.

Uncomplicated UTIs

Symptoms typically last for 2 to 4 days, and the outlook for the majority of people is very good.

Depending on the antibiotic, the course of treatment typically lasts between 3 and 10 days, with the shorter courses having great rates of success.

However, around 30% of people will have a recurrence within 6 months of the infection.

Complicated UTIs

The outlook for people with complicated UTIs will depend on the factors that have made it complicated.

Antibiotic treatment for complicated UTIs will typically last for 10 to 14 days. If the infection is recurrent, it may take several weeks to fully remove the bacteria.

Complications that can occur with a UTI include:

People should aim to speak with a doctor if they develop any of the signs of a UTI.

The Centers for Disease Control and Prevention (CDC) advises taking children younger than 3 months to a healthcare professional immediately if they develop a fever of 100.4°F (38°C) or higher.

People should also contact a doctor if they experience any side effects of antibiotics. These could include:

Uncomplicated UTIs have a very specific description. They affect females who are not pregnant and are otherwise healthy. Specific bacteria cause the infection, which affects the lower urinary tract.

The term complicated UTI refers to any UTI that falls outside of the above description. They are more difficult to treat and can lead to complications.