1955 Dalston outbreak

Beginning in January 1955, an outbreak of disease thought to be consistent with myalgic encephalomyelitis | last4occurred, 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."