Underreporting of Viral Encephalitis and Viral Meningitis, Ireland, 2005–2008

Tara A. Kelly

, Piaras O’Lorcain, Joanne Moran, Patricia Garvey, Paul McKeown, Jeff Connell, and Suzanne Cotter

Author affiliations: Health Service Executive–Health Protection Surveillance Centre, Dublin, Ireland (T.A. Kelly, P. O’Lorcain, J. Moran, P. Garvey, P. McKeown, S. Cotter); National Virus Reference Laboratory, Belfield, Dublin (J. Moran, J. Connell)

Abstract

Viral encephalitis (VE) and viral meningitis (VM) have been notifiable infectious diseases under surveillance in the Republic of Ireland since 1981. Laboratories have reported confirmed cases by detection of viral nucleic acid in cerebrospinal fluid since 2004. To determine the prevalence of these diseases in Ireland during 2005–2008, we analyzed 3 data sources: Hospital In-patient Enquiry data (from hospitalized following patients discharge) accessed through Health Intelligence Ireland, laboratory confirmations from the National Virus Reference Laboratory, and events from the Computerised Infectious Disease Reporting surveillance system. We found that the national surveillance system underestimates the incidence of these diseases in Ireland with a 10-fold higher VE hospitalization rate and 3-fold higher VM hospitalization rate than the reporting rate. Herpesviruses were responsible for most specified VE and enteroviruses for most specified VM from all 3 sources. Recommendations from this study have been implemented to improve the surveillance of these diseases in Ireland.

Encephalitis and meningitis are serious inflammatory diseases of the brain that require hospitalization for many patients and are a substantial cause of illness. Although the etiologic agent is not identified for most cases (1), viral infection has been reported as a major cause (2).
Acute encephalitis is characterized by a triad of fever, headache, and altered mental status (3). Common features include disorientation/depressed level of consciousness; disturbances of behavior, speech, or executive function; and diffuse or focal neurologic signs such as cranial nerve dysfunction, hemiparesis, or seizures (3). Capillary and endothelial inflammation of cortical vessels is a striking pathologic finding, occurring primarily in the gray matter or the gray–white junction (4). These features distinguish encephalitis from the more commonly encountered meningitis. The most common agents that cause acute viral encephalitis (VE) are herpes simplex virus (HSV) and varicella-zoster virus (VZV) (5).
A distinction must be made between acute VE and autoimmune/postinfectious encephalitis, which can occur with a variable latent phase between acute illness and the onset of neurologic symptoms (6,7). This distinction is critical because the management and prognosis are often quite different (4). Evaluation of cerebrospinal fluid (CSF) following lumbar puncture is essential for accurately diagnosing disease, unless its collection is contraindicated because of high intracranial pressure (4). In this study, we did not attempt to ascertain the prevalence of autoimmune/postinfectious encephalitis in Ireland.
Aseptic meningitis refers to a disease with acute onset of symptoms and obvious signs of meningeal involvement, in which an etiologic agent is not apparent after bacterial culture of CSF (8). The disease is often associated with lymphocytic pleocytosis without other cause. These patients usually lack altered sensorium or abnormal global or focal neurologic signs (3,4). Viruses are most commonly associated with these clinical manifestations, most frequently, enteroviruses, herpesviruses, and arboviruses (9). Under the 2003 case definitions covering this study period, laboratory evidence involving CSF analysis or immune response, in addition to clinical diagnosis, was necessary for the reporting of VE and VM to public health departments (10,11).
In this study, we examined 3 different available data sources to estimate how well data reported to public health authorities and captured by the Computerised Infectious Disease Reporting (CIDR) passive surveillance system, during 2005–2008, reflected the incidence of VE and VM in Ireland. CIDR is the real-time Internet-based surveillance system for 93.9% of all notifiable infectious diseases reportable by statute in Ireland. We compared cases reported to CIDR with laboratory detection of cases from the National Virus Reference Laboratory (NVRL) and cases identified from hospitalized patient discharge information in the Hospital In-Patient Enquiry (HIPE) scheme. In 2005, eight (24%) of the 34 public hospital laboratories, in addition to the national reference laboratories, were connected directly to CIDR. This connection increased to 16 (47%) in 2008. Hospital/community physicians who manage VE or VM patients using laboratories which were not directly connected to CIDR, were obligated to report notifiable diseases to CIDR through the local department of public health.