Clinical and Laboratory Features of Epidemic St. Louis Encephalitis

An epidemic of St. Louis encephalitis in Dallas, Tex., in 1966 again showed the characteristic clinical and epidemiological features of this disease: the occurrence of encephalitis in elderly persons in urban areas during summer and early autumn. Headache, fever, nuchal rigidity, confusion, and tremor were outstanding clinical features. Prospective sequential clinical studies commonly showed isolated cranial-nerve dysfunction, pathological reflexes, and nystagmus. Cerebrospinal fluid pleocytosis with a predominance of mononuclear cells and a normal cerebrospinal fluid glucose also were characteristic. Even though symptoms and signs suggestive of urinary tract infection were common, urine cultures for bacteria were usually negative. Electromyographic abnormalities and elevations in serum aldolase values were frequent and suggested diffuse, lower, motor-neuron dysfunction.