Onset of ME/CFS

The onset of ME/CFS can be sudden (acute) or gradual. Sudden onset is more common. Dr. Melvin Ramsay and Dr. Byron Hyde both describe sudden/acute onsets for myalgic encephalomyelitis (ME) as oppose to ME/CFS being acute or gradual. In cases of sudden onset, it is usually easy to identify the trigger of the illness, such as physical trauma, overwhelming stress, or a viral/bacterial infection. Children, particularly adolescents, will more likely have an acute illness like the flu or mononucleosis as their onset.

Acute symptoms develop over hours to days. 85% of patients report a trigger. 72% of ME/CFS patients report that a bacterial or a viral infection was their onset of ME/CFS; 4.5% trauma; 4.5% surgery or childbirth; 2.2% allergic reaction; 1.7% stress or trauma.

Genes are being considered for a risk in developing ME/CFS as sometimes several members of the same family will develop ME/CFS.

Pre-onset triggers
The International Consensus Criteria (ICC) Primer includes a patient assessment form, which includes factors that may have triggered ME, these can be infectious (for example, a virus), or non-infectious (for example, exposure to chemical toxins or severe physical injury).

Infectious exposure or events

 * minor infections, vaccination, upper respiratory infections, sinusitis, pneumonia, gastrointestinal illness (after sinusitis or pneumonia), dental infections, vaginal infection, cystitis, prostatitis, blood transfusion
 * exposure to: sick people, unfamiliar infectious agents when traveling, particularly following vaccinations, contaminated water, poor quality recycled air

Non-infectious exposure or events
Other triggers have been recognized besides these, and some people report several potential triggers or no known cause.
 * exposure to: chemical toxins, heavy metals, or moulds
 * severe physical trauma e.g. whiplash/spinal injury/surgery
 * anaesthetics
 * undue stress
 * steroids

Is ME always caused by a virus
Some ME patient charities, for example The Hummingbirds' Foundation for ME hold the view that ME is always caused by a virus, but chronic fatigue syndrome (CFS) may have non-viral triggers, and do not recognize bacterial infections or non-infectious events as a potential cause or trigger.

The onset events recognized as potential causes or triggers in the ICC are based on events prior to illness that have been reported by patients meeting the diagnostic criteria for ICC ME or based on the consensus of experts. The exact cause has not yet been identified in research. Chu et al. (2019) reported on pre-onset events for patients meeting the CFS Fukuda criteria only.

Development of ME
The ICC recognizes that ME can develop
 * suddenly
 * gradually, or
 * be infectious (for example, outbreaks within a community)

Criteria

 * In the Holmes criteria, description of the main symptom complex as initially developing over a few hours to a few days is an optional criteria for diagnosis, under the section Minor Symptom Criteria.

Notable studies

 * 2019, Onset patterns and course of myalgic encephalomyelitis/chronic fatigue syndrome (Full text)