Our study show that at least 5% of the patients with confirmed Giardia enteritis reported failure to recover with unexplained fatigue and accompanying symptoms that in the broad corresponded with a clinical entity described previously [9
]. In comparison, the prevalence of CFS in a normal population ranges between 0.23% and 0.56% in different populations [29
]. Thus, the frequency of CFS among patients with confirmed Giardia infection was at least 8 times higher than in the general population. Our findings suggest that there may be a relationship between Giardia infection and CFS. However, further studies are needed to prove that there is a causative relationship. Persisting abdominal complaints classified as diarrhoea-predominant IBS were present in 10% of the patients with confirmed Giardia infection [6
]. Similar prevalence rates of 5% with CFS and 10% with IBS have been observed in patients after campylobacter gastroenteritis [31
]. The rate of post-infectious fatigue syndrome after glandular fever has been reported to be 9% in previous cohort studies [2
The patients in our cohort represent young adults not exposed to Giardia lamblia before the contamination of the municipal water in 2004. Although Giardia lamblia is not an invasive parasite, proteins on the surface induce a humoral immune reaction [33
] and CFS pathogenesis is likely to include immunologic components. However, the relationship between inflammatory responses and post-infectious fatigue syndrome have not been documented in longitudinal studies [2
In the present study the frequency of CFS was significantly higher among females. Other studies have also reported that CFS is more frequent among females [9
]. By contrast, there was no gender difference as to the frequency of self-reported chronic fatigue two years after disease onset among the laboratory confirmed cases of Giardia lamblia in Bergen in accordance with previous community-based studies of chronic fatigue [8
There were little differences between the sexes both regarding concomitant symptoms such as abdominal symptoms and other symptoms in the early phase of the disease. However, at the time of referral females reported more severe abdominal symptoms (marginally significant).
Although the cause of CFS is unknown it is generally thought that post-infectious fatigue develops shortly after acute infection [35
]. However, more than half of our patients had a gradual onset of fatigue. Other studies have shown conflicting results as to onset of symptoms [9
]. We found that patients who developed fatigue over months, tended to have more initial abdominal symptoms than patients who developed fatigue within weeks of Giardia enteritis. A possible explanation is that many initial symptoms either masked the experience of early fatigue or the recall of early fatigue among some patients. This may be of special importance in cases of litigation where the timing of fatigue onset after acute infection may determine the question of causation.
There was a slight trend towards more stressful life events prior to Giardia enteritis among patients with fatigue development over months compared to patients with fatigue development within weeks [19
]. A possible interpretation is that whereas early onset of fatigue is caused by the Giardia enteritis, late onset of fatigue among some patients has more complex causation including psychologically stressful life events present before the Giardia enteritis [35
The patients scored significantly worse than controls on all subscale scores of SF-36 for both sexes. The scores were lowest for physical functioning and vitality whereas emotional and mental scores were only mildly impaired. The scores among our patients were remarkably similar to the scores reported among patients with CFS in a previous study [23
]. This suggests a similar disease profile among our patients and patients with CFS not related to Giardia enteritis and provides evidence that CFS exists as a discrete illness characterised by extremely low levels of physical functioning and only mild mental and emotional components [15
The patients scored significantly worse than the controls both as to anxiety and depression based on the HADS subscores [26
]. There were no sex differences between our patients as to HADS subscores. This is surprising because no males reported anxiety any time prior to disease onset while this was reported by 9 (21%) females. The CFS sufferers are not primarily depressed, and do not exhibit illness behaviour [40
]. Based on the inclusion criteria which included primary-care records, the frequencies of depression and anxiety among our patients based on HADS subscores do not represent primary depression or anxiety, but reflect co-morbid illness secondary to long-standing chronic fatigue. Others have found similar or higher HADS subscores among patients with CFS [3
]. Our patients did not disclose any abnormal neuroticism.
CFS is associated with various functional limitations both for work and social life, and assessment of functional ability including sickness abscence is necessary in medical and vocational rehabilitation [42
]. The focus on function ability represents a shift in attention from symptoms to resources, possibilities and coping. After the initial evaluation our patients entered a comprehensive multidisciplinary intervention program. The program was individualized and included education focusing on psychology and coping. Rehabilitation included physiotherapy, manageable exercise program, and occupational therapy. We plan to publish a five year follow-up study of the patients.
There has been one previous report of community outbreak of CFS possibly precipitated by Giardia enteritis comprising 11 patients [18
]. The mean age was 31 years which is similar to the mean age in the present study.
A limitation of the present study is that no systematic search for CFS among all patients with confirmed Giardia lamlia enteritis was performed. Thus, our findings represent a lower limit for the frequency of CFS after Giardia lamblia enteritis in a previously Giardia naïve population. Another limitation is that we compared our patients to published normative data and not a matched control group recruited from Bergen. Data on diseases and stressful events before the Giardia lamlia infection were based on self-report and therefore liable to failure of recall.