Background
Risk factors for, and long-term outcomes following, detection of varicella zoster virus (VZV) DNA in the cerebrospinal fluid (CSF) are unknown.

Methods
We performed a nationwide population-based cohort study of all Danish residents who had VZV DNA detected in the CSF by polymerase chain reaction (PCR) between 1 January 1997 and 1 March 2016 (VZV cohort; n = 517) and an age- and sex- matched comparison cohort from the general Danish population (n = 9823). We examined potential risk factors and mortality, neurologic morbidity, psychiatric morbidity, redemptiom of prescriptions for nervous system medicine prescribed for the nervous system, and social outcomes.

Results
Prior hospital admission, redemption of immunosuppressive medicine, comorbidity, and immunosuppressive conditions were associated with detection of VZV DNA in the CSF. Mortality was increased in the VZV cohort, especially during the first year of observation and among patients with encephalitis. Patients in the VZV cohort had an increased risk of dementia and epilepsy. The redemption of antiepileptics and antidepressants was increased in the VZV cohort.

Conclusions
Immunosuppression and comorbidity are associated with increased risk of detection of VZV DNA in the CSF and the condition is associated with increased mortality and neurological morbidity.