Clinical, epidemiological, and virological aspects of echovirus type 9 infection in Sheffield, 1960.

In the summer of 1960, a number of patients from Sheffield, and the surrounding districts were admitted to hospital with clinical evidence of acute meningitis. The studies described below showed that the causative agent most commonly incriminated was echovirus type 9, a virus not encountered in Sheffield during the previous 3 years. The association of this particular virus with aseptic meningitis, often accompanied by a rubelliform rash, was first observed in 1956 (Tyrrell and Snell, 1956; McLean and Cameron, 1957). On many subsequent occasions frank epidemics of meningitis, sharply circumscribed in time and place, have occurred with evidence of direct spread within families (Sanford and Sulkin, 1959; Sabin, Krumbiegal, and Wigand 1958; Sabin 1960). In 1956, a brisk localized outbreak of echovirus type 9 infection occurred near Sheffield (Tyrrell, Lane, and Snell, 1958), and a similar but smaller episode occurred in this region in 1957 (Heath, unpublished). In the 1960 outbreak, cases of meningitis continued to appear sporadically during a 3-month period from widely-separated areas. There appeared to be no direct contact between the patients themselves except for certain intrafamilial episodes detailed below; in fact, no single general practice in which meningitis occurred contributed more than one family to the hospital. In view of these recurrent events and the patchy nature of the 1960 outbreak, it seemed possible that echovirus type 9 was being transmitted to susceptible persons by asymptomatic carriage through a partially-immune population. An alternative possibility was that frank cases of meningitis represented only one variety of the clinical manifestations of echovirus type 9 infection, whilst the main reservoir and the bulk of virus spread might exist in some less easily recognized non-meningeal illness not normally seen in hospital practice. Because of these possibilities, virus studies were made in all members of the families in which a presumed case of echovirus infection occurred, on mild illnesses seen in a representative urban general practice over the same period of time, and also on healthy persons in the general population. Certain laboratory characteristics of echovirus type 9 strains recovered from different sources were examined to determine whether differences in their pattern of infection might be explained by variations in the biological properties of the virus.