BACKGROUND: Subacute sclerosing panencephalitis (SSPE) is a fatal complication 
of measles. We reviewed California cases from 1998-2015 to understand risk 
factors for SPPE and estimate incidence.
METHODS: SSPE cases had clinically compatible symptoms and measles antibody 
detection in cerebrospinal fluid (CSF) or medical record documentation of SSPE. 
Cases were identified though a state death certificate search, Centers for 
Disease Control and Prevention reports, or investigations for undiagnosed 
neurologic disease. Measles detection in CSF was performed by serology at the 
California Department of Public Health or at clinical laboratories.
RESULTS: Seventeen SSPE cases were identified. Males outnumbered females 2.4:1. 
Twelve (71%) cases had a history of measles-like illness; all 12 had illness 
prior to 15 months of age. Eight (67%) children were exposed to measles in 
California. SSPE was diagnosed at a median age of 12 years (3-35 years), with a 
latency period of 9.5 years (2.5-34 years). Among measles cases reported to CDPH 
during 1988-1991, the incidence of SSPE was 1:1367 for children <5 years, and 
1:609 for children <12 months at time of measles disease.
CONCLUSIONS: SSPE cases in California occurred at a high rate among unvaccinated 
children, particularly those infected during infancy. Protection of unvaccinated 
infants requires avoidance of travel to endemic areas, or early vaccination 
prior to travel at age 6-11 months. Clinicians should be aware of SSPE in 
patients with compatible symptoms, even in older patients with no specific 
history of measles infection. SSPE demonstrates the high human cost of "natural" 
measles immunity.