Sexually-transmitted infections were often misdiagnosed as UTIs, which meant that antibiotics were being inappropriately prescribed.
Fewer than half the women diagnosed with a UTI actually had one, while STIs were missed in 37 per cent of women, say researchers from the Case Western Reserve University in Cleveland, US, who had reviewed the cases of 264 women diagnosed with one of the conditions.
The researchers were able to retrieve all the urine samples and tested for sexually -transmitted infections such as gonorrhoea, chlamydia and trichomonas.
To be fair, say the researchers, there are similarities in the two conditions. They share symptoms of dysuria (painful or difficult urination), frequency and urgency. Urine analysis can also produce an incorrect diagnosis.
Nonetheless, women were often treated for a UTI even when they didn't have any of the symptoms, and without having had a urine test. In fact, 24 per cent of women diagnosed with a UTI had none of the usual symptoms, so making the wrong diagnosis even more baffling, the researchers say.
More than one million cases of UTIs are diagnosed by emergency hospital staff every year in the US, and the Centers for Disease Control and Prevention (CDC) estimates that nearly 20 million new STIs occur every year, although many go unreported, and many more are undiagnosed.
(Source: Journal of Clinical Microbiology, 2015; JCM.00670-15)