Group A streptococcus (GAS) infection is not associated with new-onset tic disorders in at-risk children, findings from a large prospective study show.
The results mean that if preteens present with a new-onset tic condition, “they’re unlikely to have it as a result of a group A streptococcal throat infection,” study author Anette Eleonore Schrag, MD, PhD, professor, department of clinical neuroscience, Institute of Neurology, University College London, told this news organization.
Therefore, clinicians should not automatically prescribe antibiotics for children with tics, which sometimes occurs, said Dr. Schrag.
The study was published online Feb. 2 in Neurology.
Ongoing controversy
Research shows that genetic and environmental factors contribute to chronic tic disorders (CTDs) and Tourette syndrome (TS). Prenatal exposure to maternal smoking and central nervous system (CNS) stimulants, as well as psychosocial stress, may play a role.
There has been an ongoing controversy regarding the possible role of GAS in tics, with some studies showing an association and others not showing a link. However, previous studies have been retrospective, registry based, or had limited sample size.
This new prospective study is the first in children without a tic disorder but who were at relatively high risk of developing one. The children were followed to assess development of streptococcal infections and tics, said Dr. Schrag.
The study included 259 children aged 3-10 years (mean baseline age, 6.8 years; over half female) who had a first-degree relative such as a parent or sibling with TS or CTD.
The average age at TS onset is 7 years, peaking in prevalence and severity at about 9-12 years. GAS throat infections are common in this age group.
Although study participants did not have tics themselves, they represented “an enriched group,” said Dr. Schrag. “Because they had family history, we knew they were at increased risk for developing tics.”
Participants were evaluated every 2 months, alternating between scheduled hospital visits and telephone interviews. Parents kept a weekly diary and were instructed to bring their child in for assessment if they showed any signs of tics.
The average follow-up period was 1.6 years, but some of the children were followed for up to 48 months. During the study, there were a total of 1,944 assessments, including 939 telephone interviews and 1,005 clinical visits.
More common in boys
Investigators defined tic onset as the first occurrence of any sudden, rapid, recurrent, nonrhythmic involuntary movement and/or vocalization on at least three separate days within a period of 3 weeks.
The investigators assessed GAS exposure using parameters from throat swabs, serum anti-streptolysin O titers, and anti-DNAse B titers.
They used multiple definitions and combinations of GAS exposures “to make sure we weren’t missing any association because we didn’t use the right definition,” said Dr. Schrag. She explained a definitive strep infection is not always clear-cut.
At baseline, 17.0% participants tested positive for GAS, and 78.8% tested negative. No throat swab was available from 4.2% of participants.
During follow-up, the number of confirmed positive GAS exposures was 59, 102, 125, and 138, depending on the definition.
Researchers identified 61 tic cases during the study period. There was no evidence of an association of tic onset with GAS exposure after adjusting for age, sex, and parental education level.
However, there was a strong association between tic onset and sex, with girls being 60% less likely to develop tics than boys (hazard ratio, 0.4; 95% CI, 0.2-0.7; P < .01).
This result wasn’t particularly surprising, as it’s known that more boys develop tics than girls. “We just confirmed that in a prospective way,” said Dr. Schrag.
Results from sensitivity analyses confirmed the results. This was also the case with analyses that excluded visits with missing data on GAS exposure and that further adjusted for clinical site and psychotropic medication use.