Cystitis is an extremely common problem in women. Estimates vary but it is thought that between 10 and 20% of women are affected by a lower urinary tract infection (UTI) at some point during their lifetime. In the United Kingdom 1 – 3% of all consultations in general practice are for urinary tract infection. There are 5.2 million consultations per year in the USA for urinary tract infections in women, with a billion dollar cost implication.
Cystitis is an inflammation of the lining of the bladder. It can be produced by an infection from bacteria, viruses, or fungi. Inflammation of the trigone area can also be produced by certain chemicals. In a bacterial infection, the organisms elicit an inflammatory response in the bladder which can be identified by the excretion of polymorphonuclear leucocytes in the urine.
The presence of bacteria in the urine is abnormal, as bladder urine is sterile.
To differentiate an infection from contamination, an arbitrary cut-off point has been uniformly recognized. This was adopted after the work of Kass in the 1950s. He quantitatively assessed the predictive value of colony-forming bacteria in urine. From his work it was established that 105 colony-forming units (c.f.u.) bacteria per ml of voided urine is a highly specific threshold for true bacteriuria, but it has a low sensitivity. Recently, Stamm has argued that the threshold should be reduced to 102 c.f.u. for coliforms as a sensitive indicator for infection in symptomatic women, men and children. Laboratories usually report in the range of 104 to >105 c.f.u./ml. The thresholds used have different meanings in different populations, and are a compromise between sensitivity and specificity.
Some women have been found to have significant bacteriuria without any symptoms. This is defined as asymptomatic bacteriuria. This is a benign condition in the elderly, but is a predictor for the development of pyelonephritis in pregnancy. It is important that pregnant women are screened for asymptomatic bacteriuria at 16 weeks by sending a urine for culture; dipstick testing for leucocyte esterase and nitrites are not adequately sensitive.
There is often vaginal contamination of a urine specimen, giving misleading results (see MSUs). Contaminated specimens usually grow a mixture of skin and faecal organisms, whereas in true bacteriuria there is usually a pure growth of a single organism. In fact, Goodfriend argues that it is virtually impossible to obtain a clean voided urine from an elderly obese female.
Uncomplicated urinary tract infections
An uncomplicated urinary tract infection is an infection of the bladder only, in an otherwise fit and well woman with no abnormality of her urinary tract, and no other major predisposing factors (Table Risk factors of occult upper urinary tract infection).
Complicated urinary tract infections
Patients who have functional, anatomical, or metabolic abnormalities are defined as having complicated urinary tract infections. All infections of the kidneys (upper urinary tract), or any infection of any part of the urinary tract in children, pregnancy, or men should also be regarded as a complicated infection.
Relapse or reinfection?
Recurrence of bacteriuria with a different organism from the original one is defined as a reinfection. This implies acquisition of a new pathogen. This is in distinction to the recurrence of bacteriuria with the original isolate, which is termed a relapse and implies persistence of the bacteria in the urinary tract.
A true chronic urinary tract infection is the persistence of the same organisms in the urinary tract for months or years. Reinfection is a much more common clinical entity than relapse.
The urethral syndrome
In about 50% of all cases of women who present with acute dysuria and frequency, the urine culture is less than 105, and so is reported as “sterile”. This is the definition of the “urethral syndrome”, also known descriptively as the frequency and dysuria syndrome. It is a topic fraught with controversy over aetiology, diagnosis, and treatment. Stamm et al. feels that most of the women with symptoms have a true bacterial cystitis, and should be treated accordingly. Maskell et al. feels that there are fastidious bacteria infecting these women, whereas O’Dowd feels that this group have more in common with irritable bowel sufferers.
Some women may have a Chlamydia infection, especially in a young, sexually active female using non-barrier contraception who has recently changed sexual partner. In the context of a “sterile” pyuria, Chlamydia, gonococcal urethritis, and tuberculosis of the urinary tract should be considered.
Table Risk factors of occult upper urinary tract infection
Presentation of cystitis
Women often present in an agony of acute dysuria, frequency, and urgency. They may have been up all night, needing to void urine every half hour to an hour. They may also have haematuria, which they may find alarming. Suprapubic pain occurs in 10% of cases.
Women with these symptoms may either have acute cystitis, acute urethritis, or acute vaginitis. The history makes the diagnosis in 90% of cases. If the woman is asked to describe the site of the pain, in acute cystitis the inflammation of the trigone area causes “inside” dysuria, whereas with acute urethritis or vaginitis the dysuria feels more on the “outside”.
If the woman presents with flank pain, low back pain, abdominal pain, fevers, rigors, sweating, headache, nausea and vomiting, malaise, or prostration, an overt upper urinary tract infection is probable. This may need in-patient hospital intravenous antibiotic treatment if she has complicating factors (Table Risk factors of occult upper urinary tract infection), or is unable to take antibiotics by mouth.
The problem with “lower urinary tract infections” is that about one-third of characteristic cases of acute cystitis also have an unrecognized infection of the upper urinary tract.