New research from Belgium suggests that the standard culture test for bacteria may return a negative result even though the patient tested actually has a urinary tract infection. The study compared women with symptoms of urinary infection – such as pain during urination and feeling an urgent or frequent need to urinate – with non-symptomatic women. With the help of a more sensitive test, it found that nearly all the symptomatic women with a negative standard test result actually did have an infection.
Lead author Dr. Stefan Heytens, a researcher at Ghent University and a practicing GP, says that their findings support the idea that, for women with symptoms of an uncomplicated UTI, there is no need to carry out a standard culture test.
Standard test is negative for many symptomatic women
Dr. Heytens and colleagues note that around 20 to 30 percent of women with symptoms of UTI who have the standard culture test have a negative result.
Negative standard test ‘assumed to mean no UTI’
If the result of the standard test is positive, then the patient may be offered a course of antibiotics. These can include fosfomycin, nitrofurantoin, or trimethoprim.
However, the researchers say that many doctors assume that if the test result is negative, then the patient does not have a UTI.
They note that there has also been a tendency, in the past, to consider women who fall into this category as having unexplained ‘urethral syndrome’, and that the cause is likely to be psychosomatic.
For their study, Dr. Heytens and colleagues compared urine samples from 220 women who went to see their doctor because they had symptoms of UTI, with those of 86 healthy women with no such symptoms.
The urine samples underwent the standard culture test and were also tested with a more sensitive method called quantitative polymerase chain reaction (qPCR), which can detect minute amounts of bacterial DNA known to cause UTIs, including Escherichia coli and Staphylococcus saprophyticus.
‘If a woman has symptoms, she probably has a UTI’
The researchers found that the standard test detected bacteria in 80.9 percent of urine samples from the symptomatic women.
However, the qPCR test detected E. coli in 95.9 percent of those samples, and S. saphrophyticus in 8.6 percent.
When the two qPCR test results were combined, they showed that 98.2 percent of the symptomatic women had an infection.
In the symptom-free, healthy volunteers, the standard test found evidence of E. coli in 10.5 percent of them, and the qPCR test found E. coli in 11.6 percent.
Dr. Heytens says that the more sensitive qPCR test found evidence of E. coli in the urine samples of nearly all the women presenting with UTI symptoms, even when their standard test returned a negative result.
“This suggests that if a woman has these symptoms, she probably does have a UTI,” he suggests, and concludes:
“Our findings support previous research which indicates that traditional testing may not be helpful in uncomplicated UTIs. However, traditional urine culture tests may still have a role to play if treatment fails or if there are signs and symptoms of a more complicated UTI.”
However, he also points out that they still do not know if antibiotics are of benefit to all women who present with UTI symptoms.
The study – by researchers from Ghent University and Ghent University Hospital in Belgium – is published in the journal Clinical Microbiology and Infection.