Cystitis is a bacterial infection, and 70-95% of cases are caused by the bacterium Escherichia coli (E.coli).1 There are many different strains of E.coli present in the bowel. Most strains are harmless and important for maintaining a healthy bowel. However, some strains are pathogenic if they reach the bladder (which is normally sterile) and they can cause an infection.

Young women, sexually active women and post-menopausal women are at the highest risk of cystitis:2,3,4

  • Sexual intercourse increases the likelihood of bacteria reaching the bladder due to the close proximity of the vagina to the urethra (see Figure 1 on the About cystitis page). The use of certain contraceptive methods, such as a diaphragm or condoms, can also increase your risk as it is thought the spermicides used with them alter the vaginal environment (vaginal microbiome), allowing E.coli and other potentially harmful bacteria to colonise.2 As the vagina is very close to the urethra, the bacteria can easily be transferred to the bladder and cause infection.

    It is important you do not cease using contraception, due to the risk of unwanted pregnancy and sexually transmitted infections (STIs). If you think spermicides, condoms or your diaphragm might be contributing to your repeated infections (you can observe a link between their use and the onset of cystitis) your physician will be able to discuss alternative contraceptive methods with you.

  • During and after the menopause, female hormone levels change significantly and post-menopausal women have much lower oestrogen levels than pre-menopausal women. This alters the vaginal environment (vaginal microbiome), causing a reduction in the number of protective 'good' bacteria covering the vaginal walls (Lactobacilli) which allows E.coli and other potentially harmful bacteria to colonise in higher concentrations.3,4 The vagina is very close to the urethra so bacteria can easily be transferred to the bladder and cause infection.

  • A personal or family history of cystitis or other urinary tract infections (UTIs) can mean you are at increased genetic risk of infection or repeat infection, especially if you were very young when you had your first infection.2,4

There are also a number of other, more general risk factors for cystitis:

  • If you have recently taken a course of antibiotics (for cystitis or another infection) you are at higher risk because certain antibiotics also target the natural, protective bacteria covering the vaginal walls, allowing E.coli to colonise.5

  • People with diabetes tend to be at a higher risk because high sugar levels in urine can encourage bacterial growth.6

  • Cystitis complicates 1-2% of pregnancies, mainly because the pressure exerted by the expanding uterus means there is slower passage of urine and the bladder is not fully emptied, potentially leading to a build-up of bacteria.7

  • Other conditions that prevent the urinary system being fully emptied, such as kidney
    stones, can also increase risk.4

  • Those who suffer from incontinence are at higher risk.3

  • If you have recently had urological surgery or a urinary catheter fitted, or have had a catheter for a long time, you may be more susceptible to infection due to urethra trauma and an increased likelihood of bacterial transfer to the bladder.3

  • Anyone with a weakened immune system is at higher risk of cystitis as their body cannot defend against the bacteria that cause infection.8

Expert advice

"The risk factors for cystitis is primary if you are a female, the second is something about sexual activity. If you have great frequency of intercourse and you have different sexual partners you are at great risk of getting urinary tract infections and also you get more recurrences.

We have two great groups. The first group might be the sexually active women in their 20s and the second group is in the menopausal area, after oestrogens would no longer be produced by the ovaries.

Other causes might be altered microbiome which means a change of the bacteria in the stomach and in the bowel. It could be by other antibiotic treatments or it could be by problem germs which you get by food or vegetables or meat. And the other point might be a genetic risk factor. If you ask the females, every fourth female would tell you that her mother or her grandmother or her sister will have the same problem."

"We have two main groups.. the first group might be the sexually active women in their 20s and the second group is in the menopausal area"

Professor Hartwig W. Bauer
Consultant Urologist