Women admitted to hospital with pelvic inflammatory disease had substantially worse outcomes if they also had endometriosis, according to a study from a single Spanish hospital.
Researchers at the Hospital Clinic of Barcelona reported that among women hospitalized with pelvic inflammatory disease, endometriosis was independently associated with roughly three times higher odds of treatment failure and recurrence, along with longer hospital stays. The study, titled "When two diseases collide," was published online in Acta Obstetricia et Gynecologica Scandinavica.
The finding is plausible, and it is not proof of anything causal. It comes from a retrospective review at one hospital, in one country, among women sick enough to be admitted.
What makes it worth reporting anyway is that these two conditions are genuinely hard to separate in a clinic, and the consequences of confusing them fall on patients who are already waiting years for answers.
Why These Two Conditions Get Confused
Endometriosis occurs when tissue resembling the uterine lining grows outside the uterus, producing inflammation, adhesions, and cyclical bleeding at sites where it does not belong. Pelvic inflammatory disease is an infection, caused by bacteria ascending from the vagina into the uterus, fallopian tubes and ovaries.
Different mechanisms entirely. Nearly identical presentations.
Both cause pelvic pain. Both can cause pain with intercourse. Both produce tenderness on examination. Both can damage fallopian tubes and impair fertility. Both can produce fever and elevated inflammatory markers, though that is more characteristic of infection. Imaging can show masses in either, and an endometrioma and a tubo-ovarian abscess can look similar enough to require careful reading.
The diagnostic delay in endometriosis is well documented and typically measured in years. Some of that delay involves women being treated for presumed infection when the underlying problem is not infectious.
The relationship also appears to run in both directions. A large Taiwanese national cohort study of more than 141,000 people published several years ago found that women with pelvic inflammatory disease had roughly three times the risk of a later endometriosis diagnosis. That study had its own significant limitation, since women investigated for one pelvic condition receive more scrutiny and are therefore more likely to be diagnosed with another.
The new study asks a different question: not whether one leads to the other, but whether having endometriosis changes how a pelvic infection behaves.
What the Study Actually Shows, and What It Cannot
The design was a retrospective cohort. Investigators looked back at records of women hospitalized with pelvic inflammatory disease and compared those with and without endometriosis.
The limitations are substantial, and the researchers report them.
It was conducted at a single center, which limits how far the results generalize. Referral hospitals see a selected population, and a specialist endometriosis unit in Barcelona will not see the same mix of patients as a community hospital elsewhere.
Endometriosis was diagnosed by transvaginal ultrasound rather than confirmed by tissue examination. Ultrasound is reasonable in expert hands, and it is also imperfect, which introduces the possibility that some women were misclassified in either direction.
Only hospitalized patients were included. Most pelvic inflammatory disease is treated in outpatient settings, and the findings say nothing about milder cases.
And it is observational. Women with endometriosis differ from women without it in ways that a records review cannot fully account for, including prior surgeries, adhesions that alter pelvic anatomy, longer histories of pelvic pain, and different antibiotic exposure histories. Any of those could contribute to a harder infection to treat without endometriosis being the operative cause.
The authors reported no specific funding and declared no conflicts of interest.
The Biological Reasoning Behind It
There is a coherent mechanistic story here, which is why the finding is worth taking seriously even at this evidence level.
Endometriosis creates a chronically inflamed pelvis with adhesions and distorted anatomy. Adhesions can wall off spaces where infection collects, which makes an abscess harder for antibiotics to penetrate. Endometriomas contain old blood, which is a favorable growth medium for bacteria. Fallopian tubes already damaged by endometriosis may drain poorly.
None of that is established by this study. It is the reason the association is biologically plausible rather than an artifact, and plausibility is a reason to investigate further rather than a substitute for having done so.
What This Means for Patients Right Now
Nothing about the diagnosis or treatment of either condition changes on the basis of one single-center retrospective study, and nobody should adjust care because of it.
There are still useful things a patient can take from it.
If you have endometriosis and develop new pelvic pain with fever, unusual discharge, or pain that feels different from your typical flare, that warrants evaluation rather than assuming it is the endometriosis. Infection on top of endometriosis is the scenario this study describes, and distinguishing it requires examination and testing, not self-assessment.
If you are being treated for pelvic inflammatory disease and are not improving as expected on antibiotics, say so promptly. Treatment failure was one of the outcomes measured here, and it is something clinicians can act on by reassessing the diagnosis, imaging, or changing therapy.
If you have persistent pelvic pain that has been repeatedly attributed to infection without a confirmed infection, it is reasonable to ask whether endometriosis has been considered. That question is worth asking regardless of this study.
Anyone with severe pelvic pain, high fever, vomiting preventing fluid intake, or feeling acutely unwell needs urgent care rather than a scheduled appointment.
What Happens Next
Confirming this would require multi-center data, ideally with histologically confirmed endometriosis and inclusion of outpatient pelvic inflammatory disease. Whether that work gets funded is a separate question, and endometriosis research has historically been under-resourced relative to its prevalence.
MedicalDaily will report on any replication and on changes to management guidance for either condition.
The confirmed finding is that in one Spanish hospital's retrospective records, endometriosis was associated with about threefold higher odds of treatment failure and recurrence among women hospitalized with pelvic inflammatory disease. The people most affected are women with known endometriosis who develop a pelvic infection. The most reasonable action is prompt evaluation of new or different pelvic symptoms rather than attributing them to a known condition. The central uncertainty is whether endometriosis worsens these infections or simply travels with other factors that do.
Frequently Asked Questions
What did the study find? Among women hospitalized with pelvic inflammatory disease, those who also had endometriosis had roughly three times higher odds of treatment failure and recurrence, plus longer hospital stays.
Does endometriosis cause worse infections? The study cannot establish that. It is an observational, retrospective analysis showing an association, not a causal test.
Why are these conditions confused? Both cause pelvic pain, pain with intercourse, and tenderness; both can impair fertility, and imaging findings can look similar.
What are the study's limitations? Single-center, retrospective, endometriosis diagnosed by ultrasound rather than tissue, and only hospitalized patients were included.
Should I do anything differently? No care changes on this evidence. If you have endometriosis and develop fever or pain that feels different from usual, seek evaluation rather than assuming it is a flare.
When should I seek urgent care? Severe pelvic pain, high fever, vomiting that prevents keeping fluids down, or feeling acutely unwell.
What if antibiotics are not working? Tell your clinician promptly. Treatment failure is actionable through reassessment, imaging, or a change in therapy.
