1955 Dalston outbreak

Beginning in January 1955, an outbreak of disease thought to be consistent with myalgic encephalomyelitisoccurred, centered around the village of Dalston in Cumbria, England and affected 233 people (14% of the practice population). Males and females were equally affected. (https://www.jstor.org/stable/4457588?seq=1#page_scan_tab_contents)

An epidemiological study of the outbreak was published by Dr. A. L. Wallis, a general practitioner that covered the areas concerned.

Symptoms

 * lymphadenopathy
 * hepatosplenomegaly
 * abnormal lymphocytes
 * Paresthesias
 * blurred vision
 * vertigo
 * depression as a significant problem
 * myalgia
 * muscle weakness (especially in lower limbs)
 * joint pain
 * cognitive dysfunction (loss of concentration manifested, inability to read, knit)
 * locomotor dysfunction
 * reticuloendothelial involvement
 * ulnar neuropathies

Findings
Wallis initially thought the infection was glandular fever, but tests came back negative.

Epidemiology
The attack rate during the epidemic was 13.9%. Endemic cases continued to appear several years after the initial outbreak and incidence of the disease spread to surrounding villages.

Prognosis
There were no fatalities. Relapses occurred in a proportion of those infected; in some cases, several relapses occurred over a period of months, symptoms being minimal or absent between the recurrences.

"Recurrences of symptoms of the disease became a well marked feature of the epidemic, and it was noted that in some instances a contact of the primary host, who was having a recurrent attack, would develop the typical disease, suggesting, therefore, that, at the time of the recurrent attack, the host was again infectious."