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Subacute Sclerosing Panencephalitis Surveillance -- United States

Subacute sclerosing panencephalitis (SSPE) is a slow-virus infection of the central nervous system associated with prior measles infection. Onset generally occurs in late childhood or adolescence and is usually characterized by the insidious onset of mental deterioration and myoclonia. Although spontaneous improvement or stabilization can occur, the vast majority of patients proceed over a period of months to years to generalized convulsions, dementia, coma, and death.

To collect demographic and clinical information on SSPE cases, a national SSPE registry was initiated in 1969 at the University of Tennesee. Since October 1980, responsibility for the registry has resided with the Medical College of Georgia.* The registry is supported by the Office of Biologics, Food and Drug Administration, and maintained in collaboration with CDC. *Inquiries and suspected case reports can be directed to Dr. Paul R. Dyken, Professor and Chief, Section of Pediatric Neurology, Medical College of Georgia, 1459 Laney-Walker Boulevard, Augusta GA 30912.

A case of SSPE is defined by CDC as an illness with a compatible clinical course plus one of the following items of supporting laboratory evidence: 1) measles antibody detected in the cerebrospinal fluid (CSF), 2) a characteristic pattern on electroencephalography, or 3) typical histologic findings in brain biopsy material or tissue obtained on postmortem examination.

As of July 1982, 634 individuals suspected of having SSPE, with onset from 1956-1981, had been reported to the registry; of these, 368 were U.S. citizens who met the case definition of SSPE and had onset of symptoms between 1969 and 1981 (Figure 1). Fifty-five percent (202) of the 368 confirmed cases had a history of only measles infection; 14% (51) had a history of only measles vaccination; and 17% (63) had a history of both, with the natural illness most frequently preceeding the vaccination. The remaining 14% (52) gave no positive history of having natural measles infection or measles vaccination.

The reported incidence rate among U.S. citizens under 20 years of age has been estimated for selected years (by year of onset of SSPE). The rate for 1970 is estimated at 0.61 per million population, decreasing to 0.35 in 1975 and 0.06 in 1980.

A crude estimate can be made of the risk of SSPE following natural measles infection by determining the year in which a given person who developed SSPE contracted measles and the number of measles cases that occurred in that year.** Similarly, the risk, if any, associated with measles vaccine can be estimated by determining the year of vaccination of patients with SSPE and the net number of doses of live-virus measles vaccine distributed during that year. The estimated risk of SSPE following natural measles infection averaged 8.5 cases per million measles cases occurring in 1960-1974.*** The estimated rate of SSPE following measles vaccination averaged 0.7 reported SSPE cases per million doses of live-virus measles vaccine distributed from 1963 (the year of vaccine licensure) through 1974. **Assuming a 10% reporting efficiency, estimated case numbers were determined by multiplying reported cases for those years by 10. ***The average interval between onset of measles and onset of SSPE is approximately 7 years. Thus, SSPE risk estimates for persons who developed measles beyond 1974 are less likely to be accurate. Reported by P Dyken, MD, R DuRant, P Shmunes, Medical College of Georgia, Augusta, GA; Surveillance, Investigations, and Research Br, Immunization Div, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: Reported SSPE cases with onset since 1973 have declined substantially paralleling the substantial decline in reported measles cases after 1964-1966 (Figure 1). The lag period between the decline in reported measles cases and the decline in reported SSPE cases is similar to the mean latent period of 7 years noted previously between natural measles infection and subsequent onset of SSPE (1). Recently reported cases have a mean latent period of approximately 10 years, indicating that many of these cases may reflect sequelae due to measles incidence from the 1960s and early 1970s.

There is often a several-year lag period between onset of SSPE and registry notification (median = 3 years). Reporting is probably not complete, in part because diagnosing the illness requires a high index of suspicion. However, surveillance efforts have increased during the past 2 years from the immediately preceeding years (e.g. by continually soliciting reports from pediatric neurologists). Therefore, the apparent decrease in case reports since 1973 is probably an accurate trend, but the apparent annual case report level since approximately 1980 must also be viewed with consideration of these factors. Because of the lag time between natural measles illness and SSPE onset and the current lag time between onset and reporting, the impact on SSPE incidence of the dramatic decline in measles incidence as a result of the measles elimination effort will not be seen for nearly another decade.

Four lines of evidence indicate that measles vaccine protects against SSPE: 1) the decrease in reported SSPE cases in recent years as measles incidence has declined; 2) two case-control studies performed in the United States which indicated that measles vaccine, by protecting against measles, reduces the chance of developing SSPE (2,3); 3) a cohort analysis of children born from 1953 to 1973 indicating that, for cohorts born since 1966, one of the first years of widespread use of measles vaccine, the incidence rate of SSPE occurring at all ages has progressively decreased (4); 4) estimates of the ratios of SSPE cases to measles cases and of SSPE cases to measles vaccinees suggest that if there is any risk of SSPE following measles vaccination, it is less than or equal to one-twelfth the risk of SSPE following measles infection. Although some cases of SSPE have developed among children who had no history of natural measles infection but who received measles vaccine, these patients may have had unrecognized measles illness (e.g., during the first year of life). Studies performed before measles vaccine licensure indicated that 15%-30% of persons without a history of measles illness had evidence of measles antibody (5). A better picture of the etiologic role of live-measles vaccine in SSPE occurrence will only be seen several years after interruption of measles transmission in this country. Based on current imperfect estimates, however, the risk, if any, of SSPE from vaccination seems extremely low.

SSPE is only one of a number of degenerative neurologic diseases. In such illnesses, testing for measles antibody in the CSF will allow the diagnosis of SSPE when applicable. In order to obtain as complete reporting as possible, health-care providers and public health personnel are encouraged to report all suspected cases to the registry.

References

  1. Modlin JF, Halsey NA, Eddins DL, et al. Epidemiology of subacute sclerosing panencephalitis. J Pediatr 1979;94:231-6.

  2. Detels R, Brody JA, McNew J, Edgar AH. Further epidemiological studies of subacute sclerosing panencephalitis. Lancet 1973;2:11-4.

  3. Halsey NA, Modlin JF, Jabbour JT, Dubey L, Eddins DL, Ludwig DD. Risk factors in subacute sclerosing panencephalitis: a case-control study. Am J Epidemiol 1980;111:415-24.

  4. Halsey NA, Modlin JF, Jabbour JT. Subacute sclerosing panencephalitis (SSPE): an epidemiologic review. In: Stevens JG, Todaro GJ, Fox CF, eds. Persistent viruses. (ICN-UCLA symposia on molecular and cellular biology, Vol XI, 1978). New York: Academic Press, 1978: 101-14.

  5. Krugman SA, Giles JP, Jacobs AM, Friedman H. Studies with live attenuated measles-virus vaccine. Comparative clinical, antigenic, and prophylactic effects after inoculation with and without gamma-globulin. Am J Dis Child 1962;103:353-63.



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