New research has failed to turn up any evidence that strep infections can cause or trigger Tourette syndrome or obsessive-compulsive disorder (OCD).

While an association can't be completely ruled out, "our data do not suggest that these infections are a major factor in the development of Tourette syndrome or OCD," Dr. Anette Schrag of University College London in the UK noted in an email to Reuters Health.

OCD is an anxiety disorder characterized by unwanted thoughts or obsessions and repetitive behaviors. Tourette syndrome is a neurologic disorder characterized by repetitive, involuntary sounds and movements called tics.

Strep infection can lead to a rare neurological condition called Sydenham's chorea, characterized by OCD-like symptoms and tics, so it's been suggested that strep could be responsible for some cases of OCD and Tourette syndrome, too. A few small studies have backed up this hypothesis.

To look at the relationship in a larger group, Schrag and her colleagues identified 255 individuals newly diagnosed with OCD, Tourette syndrome, or tics and matched them to

4,519 healthy "control" subjects.

Patients were no more likely than control individuals to have had strep infections in the 2 years before their diagnosis, the investigators report in the latest issue of the journal Neurology.

"These results do not confirm other, smaller studies done in the US, which found an association between strep infection and these brain disorders," Schrag noted in a prepared statement.

Many doctors are prescribing antibiotics to patients with OCD or Tourette syndrome, based on the idea that these conditions are strep-related, Dr. Donald L. Gilbert of the Cincinnati Children's Hospital Medical Center, who co-authored an editorial accompanying the study, told Reuters Health.

"I get patients all the time who are already taking antibiotics to treat their tics, and I stop them," he said. Gilbert said he also gets emails every week from parents asking whether their child's Tourette syndrome was caused by strep.

Parents shouldn't worry that a strep infection not treated quickly enough could have caused their child's OCD or Tourette syndrome, Gilbert said.

Nevertheless, he added, any time a child has a fever and a sore throat a prompt trip to the doctor is in order, because untreated strep infections have known serious consequences including rheumatic fever (an inflammation of the heart that can cause permanent damage), arthritis, and inflammation of the kidneys.

"Whilst the link of streptococcal infections and Tourette syndrome, tics and OCD remains a very interesting and important area of research to understand the development of these disorders," Schrag said, "patients and their families do not need to take any precautions, tests or treatments when developing a sore throat other than the same as everyone in the population."