Explaining Chronic Fatigue Syndrome and related conditions to people (employee, friends, family, etc) who has no direct experience can be a thankless, exhausting and frustrating experience.
The root problem in explaining is the listener may not be able to relate to what is being described. Often CFSers go into whatever is a current theory or the results of dozens of tests. Some conditions, like Irritable Bowel Disease, UC, or Crohn’s are easier to explain because most people have experience food that have not agreed with them — thus they have something concrete to relate to.
I have a model of what CFS is and I am inclined to explain the model. The following is my monologue….
“My illness or disease is simple to understand but very hard to treat. As a result of an illness [even if it is due to stress, I would keep to citing illness — mentioning stress will send the listener down a different path], likely flu or some travel related bug, I became sick. I recovered from it but the symptoms returned afterwards — it is sometimes called post infection syndrome. The same thing is well documented wtih giardiasis and other infections. Many of these infections have mild symptoms or are hard to detect. With the Bergen giardiasis epidemic, they estimated 1/3 of those infected did not have symptoms severe enough to see a doctor, or were false-negative to lab tests.
There is a paper from 2010 titled “Giardiasis–why do the symptoms sometimes never stop?” which cites “disturbances in the gut mucosa“. A friend, DanB, came down with CFS after a trip to central America — I believe this is one of the best documented model of how CFS occurs.
Let me explain, when you get an infection, it changes gut bacteria. The changes are very distinct and researchers have found that they can identified many diseases by just looking at the changes in gut bacteria with 90% accuracy. When you get over the infection, the gut bacteria should return to normal . The key word is should. “After giardiasis enteritis at least 5% developed clinical characteristics and functional impairment comparable to previously described post-infectious fatigue syndrome.”
“Prospective studies have shown that 3% to 36% of enteric infections lead to persistent new IBS symptoms; the precise incidence depends on the infecting organism.” 
Bergen, Norway is better than Incline Village!
In 2004, Bergen, Norway had a major epidemic of giardiasis and because of the national medical system, they were able to measure what actually happens and follow all of the patients through the years – something impossible in the US. They verified by lab tests that the giardiasis was successfully treated. They also found that infections of cryptosporidum parvum increased as a side effect. “One-third of the patients experienced recurring symptoms after treatment” 
So 1/3 did NOT return to normal within a year.
- At 2 years: “among 82 patients with persisting abdominal symptoms elicited by the Giardia infection…We found that 66 (80.5%) of the 82 patients had symptoms consistent with irritable bowel syndrome (IBS) and 17 (24.3%) patients had functional dyspepsia (FD)” 
- “Fatigue was reported by 41%, whereas 38% reported abdominal symptoms, and there was a highly significant association between these symptoms. Increasing age was a highly significant risk factor for fatigue. The symptoms were not due to chronic infection in this cohort.” at 2 years after the infection [1262 patients] 
- “Patients with post-giardiasis IBS suffer very little somatic comorbidity, suggesting that the aetiology of this form of postinfective IBS is predominantly biological in origin and may thus differ from the more common, non-postinfective forms of IBS.” 
- At 3 years, “The prevalence of IBS in the exposed group was 46.1%… Chronic fatigue was reported by 46.1%” 
- “A total of 58 (60%) out of 96 patients with long-lasting post-infectious fatigue after laboratory confirmed giardiasis were diagnosed with CFS … At the time of referral (mean illness duration 2.7 years) 16% reported improvement, 28% reported no change, and 57% reported progressive course with gradual worsening. ” 
This outbreak, like CFS, mainly affected females “Young women have previously been reported as the predominant group infected during a waterborne giardiasis outbreak, due to elevated water consumption. Here, the demographics of those subsequently infected are described, and young women again predominate. As secondary cases were not waterborne, this cannot be attributed to drinking habits.” 
In 2007, ” Both these findings subsided overtime. Increasingly, investigations could not determine a definite cause for the persistent symptoms. The very long-term post-giardiasis diarrhoea, bloating, nausea and abdominal pain documented here need further study.” and ” In conclusion, patients with Giardia-induced gastrointestinal symptoms developed both IBS and FD. They exhibited gastric hypersensitivity with lower drinking capacity and delayed gastric emptying.” 
Is giardia the source of CFS?
The answer is that it can be a cause of CFS in some. There appear to be many infections that can result in post-infection fatigue syndrome. What is striking about this epidemic is that the results matches the general population of CFS patients
- Mainly female patients (almost the same ratio of males to females – 86% female )
- 80% had IBS, this is also the rate with CFS in some studies
- Symptom improvement from tetracycline or the use of live faecal flora (quasi fecal transplant) occurs in both, and with both, disappears if not maintained.
- ” Nevertheless, short-term therapy with either antibiotics or probiotics does seem to reduce symptoms among IBS patients. It seems most likely that the benefits of antibiotic therapy are mediated through subtle and, perhaps, localized, quantitative and/or qualitative changes in the colonic flora.” 
A 2008 study on persisting symptoms after Giardia infection found that “tetracycline and folic acid for 28 days.. the improvement was significant for the T/F group…One month after treatment, in the T/F group (23.1%) .. reported global symptom improvement. Symptoms recurred in all of these, and after 1 y total symptom scores were unchanged from baseline”.
“Eighteen received treatment with rifaximin plus metronidazole (8-10 days) whereas 10 received a suspension of live faecal flora, installed into the duodenum during gastro-duodenoscopy… total customary symptom scores were barely significantly reduced (p = 0.07) after antibiotics, but were highly significantly reduced (p = 0.0009) after bacterio-therapy. However, symptom improvement following bacterio-therapy did not persist 1 year later…. High faecal excretion of fat and SCFAs suggests that intestinal malabsorption of fat and carbohydrates may play a role in the IBS-like complaints of these patients.” 
CFS is CFS — the triggering cause may be different, but the results are similar. Above we find that tetracyclines improved (temporarily) as did live faecal flora being implanted (think of fetal transplants). The problem is getting the gut bacteria back to normal and keeping it there until it is stable.
- [A modern epidemic]. 2004
- Cryptosporidium parvum infections in Bergen, Norway, during an extensive outbreak of waterborne giardiasis in autumn and winter 2004. 
- [Uncovering the giardiasis-outbreak in Bergen 2004]. 
- Effects of albendazole/metronidazole or tetracycline/folate treatments on persisting symptoms after Giardia infection: a randomized open clinical trial. 
- Persisting symptoms and duodenal inflammation related to Giardia duodenalis infection. 
- Subjective health complaints and quality of life in patients with irritable bowel syndrome following Giardia lamblia infection: a case control study.
- High rate of fatigue and abdominal symptoms 2 years after an outbreak of giardiasis.
- Antibiotic or bacterial therapy in post-giardiasis irritable bowel syndrome. 
- High rate of fatigue and abdominal symptoms 2 years after an outbreak of giardiasis. 
- Severity of Giardia infection associated with post-infectious fatigue and abdominal symptoms two years after. 
- Irritable bowel syndrome and chronic fatigue 3 years after acute giardiasis: historic cohort study. 
- Chronic fatigue syndrome after Giardia enteritis: clinical characteristics, disability and long-term sickness absence. 
- The impact of atopic disease on the risk of post-infectious fatigue and irritable bowel syndrome 3 years after Giardia infection. A historic cohort study. 
- Immunophenotyping in post-giardiasis functional gastrointestinal disease and chronic fatigue syndrome. 
- Chronic fatigue syndrome 5 years after giardiasis: differential diagnoses, characteristics and natural course. 
- Irritable bowel syndrome and chronic fatigue 6 years after giardia infection: a controlled prospective cohort study. 
- The relationship between irritable bowel syndrome, functional dyspepsia, chronic fatigue and overactive bladder syndrome: a controlled study 6 years after acute gastrointestinal infection. 
- Perceived food intolerance and irritable bowel syndrome in a population 3 years after a giardiasis-outbreak: a historical cohort study.