Rationale: Meningitis should be considered. The major categories of meningitis (e.g., bacterial causes) should first be excluded owing to their high mortality. Often the initial distinction between bacterial and viral meningitis is difficult. Viral meningitis should be considered when an outbreak occurs in the summer months, especially in children younger than 15 years of age. This seasonal predilection of some viruses (e.g., entero-viruses) can provide a valuable clue to diagnosis. Arboviral meningitis should be considered when clusters of meningitis cases occur in a region proximal to marshy lands during the summer. Aseptic (nonviral) infectious meningitides may not yield culture-positive diagnosis. Noninfectious causes are uncommon and are usually considered after other etiologies have been excluded.