A urinary tract infection might be more than just a painful nuisance for some, with new research suggesting it could raise the risk of stroke in vulnerable people.
The study of over 190 000 stroke patients found that the risk of suffering a stroke was heightened in the weeks and months following any infection that required a trip to the hospital. But urinary tract infections (UTIs) showed the strongest link.
People were over five times more likely to suffer an ischaemic stroke in the week following a UTI, versus the year before the infection, the findings showed.
Ischaemic strokes – the most common type of stroke – are caused by a blood clot that diminishes blood flow to the brain.
The researchers said the findings do not implicate milder infections that people manage at home.
"We're probably capturing more-severe infections with this study," said senior researcher Dr Mandip Dhamoon, an associate professor of neurology at Mount Sinai's Icahn School of Medicine, in New York City.
The study cannot prove that infections actually triggered strokes. But based on past research, Dhamoon said, it is biologically plausible: Infections can increase body-wide inflammation and may contribute to blood clots.
There are a lot of unknowns, though – including whether certain treatments can not only clear a patient's infection, but also reduce the risk of a subsequent stroke. That's a question for future studies, Dhamoon said.
Stroke risk factors
For now, people with risk factors for a stroke can focus on things they can control, according to Daniel Lackland, a professor of neurology at the Medical University of South Carolina.
"If you've recently been in the hospital for an infection, be even more cognisant of controlling your stroke risk factors, like high blood pressure and diabetes," said Lackland, who is also a spokesperson for the American Stroke Association.
The findings, published online June 27 in the journal Stroke, are based on more than 190 000 people who were treated for a stroke at New York State hospitals.
Most often, it was an ischaemic stroke, but close to 40 000 patients had suffered a haemorrhagic stroke – which occurs when a blood vessel ruptures and bleeds into the brain.
The researchers looked at each patient's risk of stroke in the week to four months after a hospital visit for an infection, and compared it with the risk in the previous year.
The risk gradually went down, but was still increased by twofold four months out, the investigators found.
Low absolute risk
At this point, Dhamoon said, it's not clear why UTIs would show the strongest association with stroke.
Respiratory infections, blood infections and UTIs were also tied to a heightened risk of intracerebral haemorrhage – a type of haemorrhagic stroke. Why might infections contribute to brain bleeding? Effects on blood vessel function could potentially play a role, Dhamoon said. But that can't be discerned from this study, he added.
Another point: The study looked at people's stroke risk at a particular time in relation to another time period. So even though the risk was relatively elevated after an infection, that doesn't mean it was high.
"The absolute risk to any one patient is still probably low," Dhamoon said.
Past studies, Lackland said, have implicated certain infections as a possible stroke trigger – including herpes zoster, which causes shingles.
"But this study suggests that a range of infections, if severe, are associated with stroke," Lackland said. That's important, he added, because it may help researchers figure out the "why."
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