The researchers monitored 301 adolescents with the infection. Six months after the mononucleosis diagnosis, 70 patients (24 percent) had not made a full recovery.
Thirty-nine of these subjects were diagnosed with chronic fatigue syndrome, reflecting 13 percent of the original group of 301.
Six months later, at a 12-month follow-up visit, 7 percent had chronic fatigue syndrome, and at 24 months, chronic fatigue syndrome persisted in 4 percent. That is about 20 times higher than in the general teenage population.
All 13 patients who still had chronic fatigue syndrome at 24 months were female and, on average, they reported worse fatigue at 12 months.