Researchers find 'clustering' pattern of toxoplasmic retinochoroiditis recurrence

While toxoplasmic retinochoroiditis is commonly thought to recur randomly, recurrence patterns among a study population in the Netherlands suggest that the infection can occur in clusters over time, according to a long-term study.

"Recurrence risk is influenced by patient age and duration of infection," the study authors said.

To determine possible risk factors and recurrence patterns for the infection, Gary N. Holland, MD, and colleagues reviewed medical records and clinical data for 143 patients with toxoplasmic retinochoroiditis in the Netherlands. For each toxoplasmic retinochoroiditis episode, the researchers determined patient age, the duration since the first episode, and the interval since the previous episode.

"We estimated the relationship between disease-free interval after an episode and recurrence risk," they said.

Subsequently, the investigators used Cox regression with frailty modeling to analyze the influence of host and disease factors on recurrence risk and correlated intrapatient recurrence times. A Monte Carlo test was also performed to determine the occurrence of clusters after prolonged, disease-free intervals.

A total of 323 episodes in first-affected eyes were followed-up for an average of 7.2 years, ranging from 0.3 to 41 years.

The risk for recurrence was highest immediately after an episode and declined with increasing disease-free intervals in a pattern that was consistent with clustering, the authors noted.

In addition, the relative risk of recurrence declined 72% (P < .001) with each 10-year interval since the first episode, and declined 15% for each 10-year increase in age when the first episode occurred, they added.

Patients older than 40 years of age were at a higher risk of recurrence than younger patients (P = .03).

Clusters of episodes occurred after extended disease-free intervals, according to the study, published in the June issue of American Journal of Ophthalmology.