period Subtherapeutic antiepileptic drug levels are one of the most common causes of seizures in this population The presence of fever may indicate that a febrile seizure has occurred or, if normal consciousness is not regained, that the patient has contracted a CNS infection such as meningitis or encephalitis (see Chapters 94 Infectious Disease Emergencies and 97 Neurologic Emergencies ) The new onset of afebrile generalized seizures requires a more thorough evaluation, as detailed in Chapter 72 Seizures Infection Coma-inducing infections of the CNS may involve large areas of the brain and surrounding structures, as in meningitis or encephalitis, or they may be confined to a smaller region, as in the case of cerebral abscess or empyema (see Chapter 94 Infectious Disease Emergencies ) The incidence of bacterial meningitis due to Haemophilus influenzae , Streptococcus pneumoniae and Neisseria meningitidis has diminished among vaccinated children, but these infections still occur in unvaccinated and undervaccinated patients, and in the immunocompromised Lyme disease is now present throughout the United States, and is a common cause of meningitis Meningitis may also be caused by viral (enteroviruses, herpes), fungal (Candida, Cryptococcus ), mycobacterial (tuberculosis), and parasitic (cysticercosis) organisms These nonbacterial infections usually have a slower onset of symptoms Encephalitis, or inflammation of brain parenchyma, may also involve the meninges (see Chapter 94 Infectious Disease Emergencies ) It occurs most commonly as a result of viral infection or immunologic mechanisms Mumps and measles were common causes before immunizations against these diseases, and they still occur in unimmunized individuals or in individuals in whom immunity has waned Varicella encephalitis occurs to days after the onset of rash The incidence of arthropod-borne encephalitides varies by geographic location but usually peaks in late summer and early fall The herpes simplex virus (HSV) remains the most common devastating cause of encephalitis, causing death or permanent neurologic sequelae in the majority of patients Beyond the neonatal period, HSV affects the temporal lobes most severely, leading to seizures and parenchymal swelling, which can cause uncal herniation Focal CNS infections include brain abscesses, subdural empyemas, and epidural abscesses (see Chapter 94 Infectious Disease Emergencies ) Brain abscesses occur most often in patients with chronic sinusitis, chronic ear infection, dental infection, endocarditis, or uncorrected cyanotic congenital heart disease Subdural empyema also occurs as a result of chronic ear or sinus