なぜ膀胱炎が繰り返すのですか？

最終更新日： 2026年8月15日

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I have written previously about the first episode of a bladder infection — 急性膀胱炎. This article is about what happens when it will not stop coming back, even after every course of antibiotics has been taken properly and in full. That pattern has its own name: 再発性膀胱炎.

The definition is worth knowing, because it is the threshold at which the problem stops being a run of bad luck and starts being something to investigate: two or more episodes within 6 months, or three or more within a year. It is reported in over 30% of women who have had a bladder infection. It is not life-threatening, but it takes a real toll on daily life.

Why it comes back: two accepted mechanisms

1. The bacteria themselves. 大腸菌 causes most cases, and certain strains have a particular trick: they attach to the vaginal lining and hide inside the cells of the bladder wall while the antibiotic is being taken, then emerge once the course is finished and start a new infection. This is the single best explanation for the pattern patients find so baffling — getting better on treatment, then relapsing a few weeks later.
2. The host. Reduced immunity makes reinfection easier, more frequent and more severe. Keeping general health up and any chronic condition well controlled genuinely matters here — diabetes in particular.

One point about men, since most of what is written on this subject is addressed to women. A urinary tract infection in a man is much less common, and it is never assumed to be simply bad luck: it warrants assessment of the prostate, of how well the bladder empties and of the upper urinary tract, even after a single episode.

What a proper workup looks for

Beyond those two mechanisms, there are several contributing factors that can be identified and dealt with — and this is precisely the value of seeing a urologist rather than taking another antibiotic course.

1. 行動要因 — frequency of sexual activity, multiple partners and certain vaginal products all raise the risk, particularly in younger women. One simple, evidence-supported habit: pass urine once, soon after intercourse, which flushes bacteria out of the urethra before they can travel up to the bladder.
2. Anatomy of the urinary tract — imaging can reveal correctable causes such as kidney stones or obstruction. A stone can harbour bacteria indefinitely, which is why no course of antibiotics ever fully clears the infection until the stone is dealt with.
3. 残尿 — a bladder that does not empty completely leaves a standing pool for bacteria to multiply in. Measuring it is quick and non-invasive, and it changes the management entirely when it is found.
4. Hormonal factors — after the menopause, falling estrogen depletes the vaginal Lactobacilli that normally keep E. coli at bay. Topical vaginal estrogen restores that protective flora and is one of the more effective measures available in this group.

One practical addition to that list: ask for a urine culture while you still have symptoms, before the next antibiotic is started. Repeated courses given without ever identifying the organism are how resistant strains develop, and they also make it impossible to tell a genuine reinfection from a symptom that was never bacterial in the first place.

The reason this list matters is that three of the four are things no amount of antibiotics will fix. If your infections keep returning, the useful question is not which antibiotic to try next but what is being missed — and that is what a proper evaluation is for.

While you are waiting for that evaluation, some symptoms should not wait at all. Fever with pain in the flank or back, shaking chills, nausea and vomiting, or feeling very unwell suggest the infection has reached the kidney and need same-day medical care. So do visible blood in the urine, an infection during pregnancy, and symptoms that fail to settle within 48 hours of starting an antibiotic.

Once any correctable cause has been dealt with, there are also several non-antibiotic ways to reduce recurrence.

再発性の膀胱炎にお悩みで、包括的な評価と個別化された予防計画をご希望の場合は、ソアラウィー・ウィーラソポーン医師がバンコク病院本社で専門医の診察を提供しております。. 診療をご予約. サミティウェート・シーラチャ病院のご予約は、泌尿器科（電話番号：）までお問い合わせください。 088-022-1445.

Bangkok Hospital also runs a Telemedicine service, which is a reasonable way to review your pattern of infections and past culture results and to plan what needs testing — the imaging, the bladder-emptying measurement and the cultures themselves are then arranged in person. Arrange it in advance by email to the Urology department at bhquro@bdms.co.th. Samitivej Sriracha is in-person only. An infection you have right now, particularly with fever, needs to be seen rather than discussed by video.

再発性膀胱炎に関するよくある質問

免責事項 This content is written and reviewed by Dr. Soarawee Weerasopone, a board-certified urologist at Bangkok Hospital Headquarters. It is intended for educational purposes only and does not constitute medical advice. Fever with flank pain needs same-day medical assessment. No medical advice, diagnosis or prescription is provided through personal messaging channels. Always consult a qualified healthcare professional before starting any medical treatment.