There were 301 adolescents enrolled in the study. Six months following their IM diagnosis, 286 (95%) completed a telephone screening interview. Based on the screening interview, 70 of these adolescents (24%) were assessed as not fully recovered. A clinical evaluation was completed on 53 (76%) of these 70 not fully recovered adolescents; 12 refused, 3 had exclusionary diagnoses (primary depression, transverse myelitis, anorexia) and 2 did not meet study criteria (the fatigue predated the IM or the subject was not able to complete the 6 month evaluation in a timely fashion). There was no significant difference in sex, family socioeconomic status or subject age between the group that completed the 6 month evaluation (N=53), the group (N=12) that refused or the group (N=5) that was excluded (data not shown).
Following the 6 month clinical evaluation, 39 of the 53 not fully recovered subjects who underwent clinical evaluation were classified as having CFS (13% of the original sample of 301 adolescents). Compared with the other 262 enrolled subjects in the cohort, 35 of the 39 subjects with CFS at 6 months were female (90%, vs 68%, p=0.01 by Fisher’s exact test). There was no difference in race or socioeconomic status between the entire cohort and the subjects who went on to develop CFS (data not shown).
Among the 14 other subjects completing the 6 month clinical evaluation, 1 had recovered between the time of the phone interview and the time he/she was seen in Clinic and 13 were classified as CFS explained (1 abused drugs, on more careful questioning 1 subject’s fatigue predated the mononucleosis, 1 had an eating disorder, 1 had an unrelated medical illness, 6 had underlying psychiatric diagnoses, 2 had psychiatric and sleep disorders, and 1 had an intercurrent acute parvovirus infection following IM, so symptoms could not be solely explained by infectious mononucleosis). There was no difference in family socioeconomic status or subject age between the group diagnosed with CFS (N=39) and the group (N=13) with CFS-explained (data not shown). All subjects evaluated at 6 months were at least Tanner stage 4.
Thirty-six subjects diagnosed with CFS at the 6 month evaluation were re-evaluated at 12 months (3 of the CFS patients diagnosed at 6 months were lost to follow-up): 11 recovered, 3 were now classified as CFS-explained (2 abused drugs and 1 had a pregnancy and miscarriage), leaving 22 with a diagnosis of CFS (7% of the original sample; all females). At the 24 month evaluation, 3 more subjects with CFS were lost to follow-up since the 12 month evaluation. Of the 19 remaining subjects diagnosed with CFS at 12 months: 6 more recovered, 2 developed a reason for their CFS (psychiatric and/or eating disorders), 1 subject thought to have recovered at 12 months developed symptoms again and was reclassified as CFS, and 1 subject thought to have CFS-explained at 12 months (the subject with the pregnancy and miscarriage) now met criteria for CFS and had no predisposing reason, leaving 13 subjects (all females) who were classified as CFS 24 months following monospot-positive IM (4% of the original sample of 301 adolescents). documents the CFS status of subjects seen at 6, 12 and 24 months.
Follow-up summary for screened non-recovered participants (N=70)
At all time points examined, significantly more persistently fatigued subjects were female (). When the course of fatigue over time was examined for the 13 adolescents who retained the diagnosis of CFS at 24 months, using the Chalder Fatigue Scale, there was a general trend for the fatigue to peak at 12 months (data not shown). There were no significant associations between treatment of the acute episode of mononucleosis with steroids and the development of CFS at 6, 12 or 24 months: 11 of 39 (28%) of adolescents who developed CFS at 6 months and 11 of 50 controls (22%) were treated with steroids, as were 7 of 22 (32%) with CFS at 12 months, and 4 of 13 (31%) among those with CFS at 24 months (all p>.05).
Frequencies and Percentages of CFS by Gender