A retrospective review of acute encephalitis in adults in Auckland over a five-year period (2005-2009).

We conducted a retrospective audit of the outcomes of patients 15 years of age and older from the greater Auckland region who had a diagnosis of encephalitis over a five-year period. Patients were identified via a database search of all patients who had a cerebrospinal fluid (CSF) viral polymerase chain reaction (PCR) panel requested between 2005 and 2009. All CSF viral PCR were performed at one laboratory. This test was used as a default marker for patients who may have had encephalitis. There were 37 patients who met our definition of encephalitis during the study. Their ages ranged from 15 to 88 years (median 51 years), and 59% were female. There was an admission rate of 7.4 admissions per year or an annual incidence of approximately 0.5 cases per 100,000. An infective cause was found in 10 patients (27%): varicella zoster in five patients (14%), herpes simplex in four (11%) and enterovirus in one patient (3%). An autoimmune paraneoplastic encephalitis was felt most likely in three patients (8%); a paraneoplastic antibody screen was performed in two of these three but was negative in both. The cause of encephalitis was not identified in the other 24 patients (65%). There were five deaths (in-hospital mortality rate 14%). Encephalitis is an uncommon but important disease, because of the significant mortality. The cause of encephalitis remained undetermined in two-thirds of patients.